Blender Compositing and Post Processing - The

Blender Compositing and
Post Processing
Learn the techniques required to create believable
and stunning visuals with Blender Compositor
Mythravarun Vepakomma
Blender Compositing and Post Processing
Copyright © 2014 Packt Publishing
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First published: January 2014
Production Reference: 1140114
Published by Packt Publishing Ltd.
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ISBN 978-1-78216-112-7
Cover Image by Mythravarun Vepakomma (
Mythravarun Vepakomma
Olivier Amrein
Project Coordinator
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About the Author
Mythravarun Vepakomma was born in Hyderabad, India, in 1983 and is currently
working as a CG Supervisor at Xentrix Studios Pvt Ltd, India. Though he graduated
in Electrical and Electronics Engineering in 2004, he has always had a great passion
for comics and cartoons. During his studies, his passion got him attracted to web
designing and 3D animation.
Mythravarun always believed in transforming his passion into a career. He decided
to go for it and started learning 3D graphics and web designing on his own. He also
started working as a part-time illustrator and graphic designer. After consistent efforts,
he finally moved into the field of 3D animation in 2005 to chase his dream of making it
his career.
He has a decade of experience in several TV series, theme park ride films, and features.
He now deals with creating and setting up CG lighting and compositing pipelines,
providing a creative direction for CG Projects, research and development on several
render engines to create a stable future for the studio, and many more things.
Midway through his career, Mythravarun encountered Blender and was fascinated by
its features and the fact that it was an open source software. This made him dig deeper
into Blender to get a better understanding. Now he prefers to use Blender for many of
his illustrations.
As a hobby and secondary interest, he composes music and writes blogs on social
awareness. His online presence can be found at the following links:
Personal website:
Music and entertainment:
I thank my wife, Harini Vepakomma, in facilitating and supporting me in writing
this wonderful book. I appreciate my loving son, Sri Vishnu Sushane Vepakomma,
who allowed me to concentrate on writing the book instead of spending time with
him. I also thank the Packt Publishing team for providing me with this opportunity
and their support. I am grateful to everyone in my career who helped me gain
knowledge and build my personality.
About the Reviewers
Olivier Amrein is a generalist in 3D art and is based in Switzerland.
He worked and has given presentations in the following countries:
Switzerland, China, Netherlands, Venezuela, Brazil, and Russia.
I would like to acknowledge and thank my wife and my two lovely
kids, Milla and Louis.
Alexey Dorokhov is a software developer. His professional interests include
distributed systems, network protocols, and machine learning. Alexey enjoys
experimenting with real-time 3D graphics. He prepares most of his 3D assets
in Blender, which involves some low poly modeling and lots of scripting.
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With lots of love and respect, I dedicate this book to my dad, Madhusudana Rao
Vepakomma and to my mom, Vasantha Lakshmi Vepakomma.
Table of Contents
Chapter 1: Blender Compositing – Overview
Understanding CG compositing
Blender's significance as a compositor
Getting started
Supported image formats in Blender
Supported color modes in Blender
Supported color depths in Blender
Blender's color spaces
The RGB color space
The HSV color space
The YUV color space
The YCbCr color space
Render layers/passes
Render layers
Render passes
Chapter 2: Working with Blender Compositor
Composite node types
Getting familiar with the compositing user interface
Node Editor
UV / Image Editor
Color management and linear workspace
Handy shortcuts for Blender Compositor
Table of Contents
Chapter 3: Working with Input and Output Nodes
How to import or export from a compositor?
Input nodes
The Render Layers node
The Image node
The Movie Clip node
The RGB node
The Value node
The Texture node
The Time node
The Mask node
The Bokeh Image node
Output nodes
The Composite node
The Viewer node
The Split Viewer node
The File Output node
The Levels node
Chapter 4: Image Manipulation Techniques
Understanding image manipulation
The Bright/Contrast node
The Hue Saturation Value node
The Color Correction node
The RGB Curves node
The Color Balance node
The Mix node
Master, Highlights, Midtones, and Shadows
Gamma, Gain, and Lift
Mask socket
Grading by setting the black and white levels
Grading using the Bezier curve
Blending modes
Use Alpha
The Gamma node
The Invert node
The Hue Correct node
Transformation tools
[ ii ]
Table of Contents
Chapter 5: Beyond Grading
The Normal node
The Fresnel effect
Depth of Field
The Defocus node
The Bokeh type
Gamma correct
Use Z-buffer
The Bilateral Blur node
The Blur node
Optical distortions
The Glare node
The Lens Distortion node
The Despeckle node
The Filter node
Motion blur
The Vector Blur node
The Directional Blur node
Texture mapping
The Map UV node
Chapter 6: Alpha Sports
What is an Alpha channel?
Alpha modes in Blender
Visualizing alpha in Blender
Significance of alpha in the layering concept
[ iii ]
Table of Contents
Layering in Blender with the alpha channel
Layering with the Mix node
Layering with the Alpha Over node
Fringe issue
Generating mattes using the ID Mask node
Edge filtering
Inverting values
Value and luminance
Inspecting a green/blue screen footage
The Difference Key node
The Distance Key node
The Luminance Key node
The Color Key node
The Channel Key node
[ iv ]
Blender Compositing and Post Processing is a one-stop solution to attain state-of-the-art
compositing skills to create mind-blowing visuals and productive composites using
Blender Compositor.
What this book covers
Chapter 1, Blender Compositing – Overview, provides a basic understanding of the
role of compositing in a CG workflow and Blender's importance as a compositor.
It also provides an understanding of what can go in and out of Blender Compositor
in terms of formats, color space, passes, layers, and bit depths.
Chapter 2, Working with Blender Compositor, explains the Blender Compositor's
node-based architecture, different types of nodes, and working in linear
workspace using color management. Many useful compositor shortcut
keys are detailed in this chapter.
Chapter 3, Working with Input and Output Nodes, covers different ways to get
data in and out of Blender Compositor. These nodes essentially form the head
and tail of the compositing flow.
Chapter 4, Image Manipulation Techniques, explains the different image manipulation
nodes and their utilization procedures available in Blender Compositor.
These nodes play a major role in grading a footage to attain a desired look.
Chapter 5, Beyond Grading, deals with advanced compositing techniques beyond
grading. These techniques emphasize alternate methods in Blender Compositing
for some specific 3D render requirements that can save lots of render times,
thereby also saving budgets in making a CG film.
Chapter 6, Alpha Sports, provides an understanding of the significance of the alpha
channel and some issues related to it. Different matte extraction techniques such as
keying, Matte ID, and masking are detailed in this chapter through practical examples.
What you need for this book
Readers should have basic lighting and shading knowledge of Blender to be able
to comprehend and extract the required passes for compositing. Blender 2.68 is
used in this book.
Who this book is for
This book is for digital CG artists longing to add photo realism and life to their footage.
This book also assists technical CG artists to strategize and implement productive
lighting and compositing pipeline in CG filmmaking. If you are new to Blender
or compositing, do not worry because this book guides you using a step-by-step
approach to help you gain compositing skills.
In this book, you will find a number of styles of text that distinguish between different
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their meaning.
New terms and important words are shown in bold. Words that you see on the
screen, in menus or dialog boxes for example, appear in the text like this:"Relighting
is a compositing technique to add extra light information."
Tips and tricks are shown like this.
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Blender Compositing –
This chapter provides a basic understanding on the role of compositing in a CG
workflow and Blender's importance as a compositor. The following is a list of
topics covered in this chapter:
• Compositing significance in the CG pipeline
• Significance of Blender as a compositor
• Blender-supported formats
• Blender color modes and depths
• Blender color spaces
• Understanding the render layers and render passes concepts
Understanding CG compositing
CG compositing is an assembly of multiple images that are merged and modified
to make a final image. Compositing happens after 3D rendering, as seen in a typical
CG pipeline flow, which is the most expensive phase of CG filmmaking. A well
planned lighting and compositing pipeline can optimize render resources and also
provide unlimited image manipulation functionalities to achieve the desired look
for the film. Though compositing is at the end of the pipeline, with its wide range
of toolsets, it can help to avoid the work of going back to previous departments
in the CG pipeline.
Blender Compositing – Overview
The following diagram depicts a CG pipeline flow and also shows where the
composite process fits in:
The strength of compositing lies in modifying the rendered CG footage into a
believable output. The following screenshot portrays a Composited Output image
done from rendered passes. Many effects such as glare, color corrections, and
defocus make the output seem more believable than the rendered beauty pass,
which is shown as the first image in Render Passes.
Chapter 1
Compositing also provides tools to grade an image to achieve extreme or fantasy
style outputs. The following screenshot illustrates different types of grades that
can be performed:
Blender's significance as a compositor
Blender is the only open source product with a range of features comparable to
other industry standard commercial or proprietary software. It provides a unique
advantage of combining 3D and 2D stages of CG filmmaking into one complete
package. This gives tremendous control when planning and executing a CG pipeline.
Automating and organizing data flow from 3D rendering to compositing can be
achieved more easily in Blender compared to other solutions, since compositing
software is separate from the 3D rendering software.
Getting started
To be able to get most out of Blender Compositor, it is essential to have a superficial
understanding of what Blender can offer. This includes supporting formats, color
modes, color spaces, render layers, and render passes.
Blender Compositing – Overview
Supported image formats in Blender
Blender's image input/output system supports regular 32 bit graphics (4 x 8 bits)
or floating point images that store 128 bits per pixel (4 x 32 bits) or 64 bits per pixel
(4 x 16 bits). This includes texture mapping, background images, and the compositor.
These attributes are available in output properties as shown in following screenshot:
Supported color modes in Blender
The color modes are the options available to view the channel information of a
footage, they are:
• BW: Images get saved in 8 bits grayscale (only PNG, JPEG, TGA, and TIF)
• RGB: Images are saved with RGB (color)
• RGBA: Images are saved with RGB and Alpha data (if supported)
Supported color depths in Blender
Image color depth, also called bit depth, is the number of bits used for each color
component of a single pixel. Blender supports 8, 10, 12, 16, and 32 bit color channels.
Blender's color spaces
The mathematical representation of a set of colors is termed as color space. Each
color space has a specific significance and provides unique ways to perform image
manipulation. Depending on the task in hand, the color space can be chosen. Blender
supports the RGB color space, the HSV color space, the YUV color space, and the
YCbCr color space.
Chapter 1
The RGB color space
The RGB (red, green, and blue) color space is widely used in computer graphics
due to the fact that color displays use red, green, and blue as three primary additive
colors to create the desired color. This choice simplifies the system's design and you
can benefit from a large number of existing software routines since this color space
has been around for a number of years. However, RGB is not suitable when working
with real-world images. All three RGB components should be of equal bandwidth to
generate a color, resulting in a frame buffer that has the same pixel depth and display
resolution for each RGB component. So, irrespective of modifying the image for
luminance or color, all three channels have to be read, processed, and stored. To avoid
these limitations, many video standards use color spaces that provide luma and color
as separate signals.
The HSV color space
HSV stands for hue, saturation, and value. This color space provides flexibility
to be able to modify hue, saturation, and value independently. HSV is a
cylindrical co-ordinate representation of points in an RGB color model.
The following screenshot shows RGB in comparison to HSV values to
attain a red color:
The YUV color space
The YUV color space is used by the Phase Alternating Line (PAL), National
Television System Committee (NTSC), and Sequential Color with Memory
(SECAM) composite color video standards for color televisions. Y stands for
the luma component (the brightness), and U and V are the chrominance (color)
components. This color space was intended to provide luma information for black
and white television systems and color information for color television systems.
Now, YUV is a color space typically used as part of a color image or CG pipeline
to enable developers and artists to work separately with luminance and color
information of an image.
Blender Compositing – Overview
The YCbCr color space
The YCbCr color space was developed as a digital component video standard, which
is a scaled and offset version of the YUV color space. Y is the luma component and Cb
and Cr are the blue-difference and red-difference chroma components. While YUV is
used for analog color encoding in television systems, YCbCr is used for digital color
encoding suitable for video and still-image compressions and transmissions, such as
Render layers/passes
To optimize render resources and also be able to provide full control at the
compositing stage, a CG lighting scene is split into multiple render layers
and render passes.
Render layers
A typical lighting scene consists of two to three characters, props, and one set.
To provide an opportunity to re-render only required elements in the scene,
each element is separated into its own render layer for rendering. All interaction
renders are also separated into render layers. The following list shows a typical
render layer classification.
• Character 1
• Character 2
• Character 3
• Characters cast shadow
• Characters occlusion
• Set
• Set occlusion
• Set interaction with characters
Render passes
Passes or AOVs (arbitrary output variables) are intermediate computational results
that are shown when rendering a layer. All render passes are buffered out when
rendering a render layer and written as separate data. These passes can be utilized
in compositing to rebuild the beauty of the render layer and also allow us to tweak
individual shader/light contributions. The following screenshot shows the Blender
internal render engine's Passes panel:
[ 10 ]
Chapter 1
Every render layer in Blender, by default, is equipped with these render passes,
but the content in the render passes is based on the data available to the render
layer. However, the pass definition and the type of content it stores doesn't vary.
All passes that have a camera icon beside them can be excluded from the combined
pass data by clicking on the camera icon. This provides another level of control over
the content of the combined pass.
Each passes' significance and content
The following screenshot shows outputs of different render passes available, by
default, in Blender's internal render engine. Their significance is explained as follows:
• Combined: This renders everything in the image, even if it's not necessary.
This includes all the options blended into a single output, except those
options that you've indicated should be omitted from this pass as indicated
with the camera button.
[ 11 ]
Blender Compositing – Overview
• Z (Z depth): This map shows how far away each pixel is from the camera.
It is used for depth of field (DOF). The depth map is inverse linear
(1/distance) from the camera position.
• Vector: This indicates the direction and speed of things that are moving.
It is used with Vector Blur.
• Normal: This calculates lighting and apparent geometry for a bump map
(an image that is used to fake details of an object) or to change the apparent
direction of the light falling on an object.
• UV: This allows us to add textures during compositing.
• Mist: This is used to deliver the Mist factor pass.
• Object Index (IndexOB): This is used to make masks of selected objects
using the Matte ID Node.
• Material Index (IndexMA): This is used to make masks of selected material
using the Matte ID Node.
• Color: This displays the flat color of materials without shading information.
• Diffuse: This displays the color of materials with shading information.
• Specular: This displays specular highlights.
• Shadow: This displays the shadows that can be cast. Make sure shadows
are cast by your lights (positive or negative) and received by materials.
To use this pass, mix or multiply it with the Diffuse pass.
• Emit: This displays the options for emission pass.
• AO: This displays ambient occlusion.
• Environment: This displays the environment lighting contribution.
• Indirect: This displays the indirect lighting contribution.
• Reflection: This displays the reflection contributions based on shader
attributes that are, participating in the current render.
• Refraction: This displays the refraction contributions based on shader
attributes that are participating in the current render.
[ 12 ]
Chapter 1
The following screenshot shows some outputs of Blender's default render passes:
This chapter introduced the CG compositing stage and Blender's significant
advantage as a compositor. We also obtained an understanding on what can go
in and out of Blender Compositor in terms of formats, color spaces, passes, layers,
and bit depths. The next chapter deals with Blender's node-based architecture and
user interface.
[ 13 ]
Working with Blender
This chapter explains the node-based architecture of Blender Compositor, linear
workflow, and user interface panels. Following is the list of topics covered in this
• Node-based architecture
• Types of compositing nodes
• Node Editor
• UV / Image Editor
• Color management and linear workspace
Blender Compositor is built on an efficient node-based architecture.
Every transformation tool in Blender Compositor is defined as a node,
building a directed acyclic graph (DAG) from source input to output image.
This process of building graphs using individual transformation tools is termed
as node-based workflow. This architecture provides flexibility to tweak parameters
procedurally. The connectors that connect these individual nodes are called noodles.
Working with Blender Compositor
Composite node types
Every individual node performs a specific operation, and many such nodes are
linked progressively to form a compositing flow. These nodes can be classified
into three categories based on the functional similarities:
• Input nodes: These nodes are used to get the image's information into
Blender Compositor's workspace
• Output nodes: These nodes save or display the result of the node graph
• Transformation nodes: These nodes are used to modify or combine the
input media
Getting familiar with the compositing
user interface
Blender Compositor UI is very intuitive yet powerful. Layout switcher,
shown in following screenshot, can be used to switch to the compositing
workspace. This UI primarily consists of two modules:
• Node Editor: This is the workspace where the node graph can be built
• UV Image Editor: This is to view the result of a complete node graph
or part of it
Alternatively, the UI can be customized by splitting or joining the layout as per
requirement, as shown in the following screenshot. Moving the pointer to any
edge of the panel turns the pointer into a two-sided arrow. Then, right-clicking
will show you options to split or merge the panel as per your requirement.
The customized layout can be saved as a scene preset in layout switcher.
[ 16 ]
Chapter 2
The following screenshot shows a typical compositing environment with all the
relevant panels:
[ 17 ]
Working with Blender Compositor
Node Editor
The Node Editor has a menu panel and workspace area as shown in following
screenshot. The menu panel has all the menu items required to create the nodes
and view options. The workspace area is where the graph will be built. As an initial
set up, the Use Nodes checkbox in the menu panel has to be checked. The Add menu
in the menu panel can be used to find all of the available Blender' Compositor nodes,
which will automatically be populated in the workspace area when selected.
The Backdrop checkbox provides a means to be able to project the viewer node's
output as background in the workspace area. When working in the Node Editor,
use the left mouse button to move the selected nodes, roll the mouse roller to
zoom the view, click on the node, and move the mouse roller to pan the view:
Media can be dragged and dropped on to the Node Editor's workspace. All nodes
can be connected using the round dots called sockets attached to nodes. To be able
to view the image in backdrop, we need to check Use Nodes and create a viewer
node by navigating to Add | Output | Viewer, as shown in the following
screenshot. Then, the connections can be made by clicking and dragging on the
round socket dots and dropping them on the input socket dot of the other node.
[ 18 ]
Chapter 2
When Use Nodes is enabled, Blender creates a render layer and composite nodes
by default. The render layer carries the 3D render data from the current Blender
scene file. Composite node renders the result of the node flow connected to it
when the render is invoked (the F12 key for current frame or Ctrl + F12 for
animation). This is done by switching on the Compositing checkbox in the Post
Processing option in the properties editor, as shown in following screenshot:
[ 19 ]
Working with Blender Compositor
The noodles curvature can be modified by selecting User Preferences in the current
editor type as shown in the following screenshot. Alternatively, User Preferences
can be found in the File menu available on top-left screen of the Blender UI:
UV / Image Editor
UV Image Editor also has a menu panel and workspace area. As shown in the
following screenshot, Browser helps in choosing which output to be viewed and
Pass Select helps in showing the render passes of the media selected in the browser.
This selected data is displayed in the workspace area. An advantage of using this
editor to view the output instead of the backdrop in the Node Editor is that the left
mouse click shows pixel information, such as R, G, B, H, S, V, and A:
[ 20 ]
Chapter 2
UV / Image Editor also provides histogram and waveform displays, shown
in the following screenshot, to perform precise grading. These options can be
displayed by clicking on the Scopes menu item in the View menu as shown
in following screenshot:
[ 21 ]
Working with Blender Compositor
Color management and linear workspace
Display devices don't display the images exactly as they get them but rather display
them with reduced gamma values, as represented in the following screenshot.
Gamma is a unit that describes the relationship between the voltage input
and the brightness of the image on your display screen. It defines the
relation between the numerical value of a pixel and its actual luminance.
All digital image-processing software saves images with increased gamma
values to counter the loss in display, thereby providing an accurate picture to the
user. All this happens behind the UI and doesn't provide any control to the user.
So, any modifications attempted on these images with baked gamma will not
provide expected results.
Color management will help in creating a workflow that allows the user to work on
the actual image instead of the gamma-corrected image. The following screenshot
shows Blender's Color Management options:
[ 22 ]
Chapter 2
When color management is enabled, it introduces a reverse gamma curve on the
image to switch it back to original gamma and also applies gamma correction
before sending it to the display device. This work state is termed as linear
workspace, explained in following screenshot:
[ 23 ]
Working with Blender Compositor
Handy shortcuts for Blender Compositor
Blender, by default, is equipped with shortcuts for most of the commonly used
operations. The following list highlights shortcuts that will come in handy when
working in Compositor:
• Shift + A: This displays the Add menu at the pointer's location.
• Ctrl + Shift + left mouse button: Applying this on any node connects its
first output socket to the viewer node. Repeating this multiple times will
cycle the connections on all the available output sockets.
• Ctrl + left mouse button: This is used to cut the noodle connections.
• X: This deletes the selected node.
• Ctrl + X: This deletes the current node and connects the previous node to
the next node.
• Alt + middle mouse button: This pans the backdrop image.
• Shift + D: This duplicates the selected node or noodle network.
• Ctrl + left mouse button: This toggles between layout presets.
• H: This collapses the node.
• Shift + H: This hides/unhides the node preview.
• Ctrl + H: This hides/unhides the unconnected sockets of a selected node.
• A: This selects all the nodes.
• B: This is used to drag the selected nodes.
• G: This grabs the node.
• F: This connects the selected nodes.
• M: This mutes the selected node.
• S or R: These can be used to scale or rotate the selected nodes. This is
useful to rearrange the node flow.
• Shift + Space bar: This maximizes/minimizes the panel.
This chapter explained the Blender Compositor's node-based architecture, different
types of nodes, and working in linear workspace using color management. The next
chapter deals with the in-depth working procedures of input and output nodes
available in Blender Compositor.
[ 24 ]
Working with Input and
Output Nodes
This chapter illustrates all the input and output nodes available in Blender
Compositor, essential for importing or exporting data from it. The following
is the list of topics covered in this chapter:
• Input nodes
• Output nodes
How to import or export from a
Input nodes are used to import footage into the Node Editor. Output nodes are used
to export or display the result of a node graph. So, these nodes form the head and tail
of the node flow drawn in Blender's node graph UI.
Input nodes
Input nodes are used to generate footage or to feed footage into the flow. These
nodes don't have any input sockets. At any instance, there will be multiple types of
inputs that a node flow might require, as shown in following screenshot and listed
as follows:
• A color or value
• A procedurally generated pattern or texture
• A rendered static or sequence of images
Working with Input and Output Nodes
• A movie clip
• Data rendered through the active camera of the current scene
The Render Layers node
The Render Layers node inputs the rendered data through the active camera of the
current scene. As shown in following screenshot, the node displays all the available
passes, render layers and scenes present in the current rendered file. Multiple Render
Layers nodes can be used to pick different layers or scenes from the rendered data of
the current Blender file:
[ 26 ]
Chapter 3
The Image node
The Image node loads images or image sequences into the Node Editor, exposing
all channels of the image. This node can also input the Alpha and Z depth channels,
if the image contains them. An image that's loaded in the UV Image Editor can also
be picked using this node. Dragging and dropping an image into the Node Editor
automatically loads the image into the Image node. When OpenEXR Multilayer is
chosen as the format for a render image in render settings, all enabled render passes
are stored in the same image. After rendering, this image can be dragged on to the
Node Editor; Blender imports the image using the Image node, with all passes saved
in their respective buffers.
The Movie Clip node
The Movie Clip node can load any movie file supported by Blender. The open
folder icon is used to browse the required clip.
The RGB node
The RGB node loads a fixed color. The color can be chosen from the color wheel
and a vertical value bar seen on the node. Alternatively, a bigger color wheel
can be obtained by clicking on the colored rectangle at the bottom of the node.
This value can be inserted to animate the image by right-clicking on it
and clicking on Insert Keyframe.
The Value node
Similar to the RGB node, the Value node loads a constant value to the flow.
The Value slider provided at the bottom of the node can be used to attain the
required value. A value can be manually entered by left-clicking the slider or by
left-clicking on it, holding, and dragging the values. This value can be keyed
to animate by right-clicking on it and clicking on Insert Keyframe.
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Working with Input and Output Nodes
The Texture node
The Texture node can load any texture that's available in the current Blender file
or from Blender's procedural texture library, as shown in following screenshot:
The Color socket outputs the RGB channel of the texture and the Value socket
outputs the Luminance channel of the texture. The Offset and Scale parameters
can be used to modify the texture. This modification will not affect the texture itself.
The Time node
The Time node also loads a value similar to a value node, but the difference is that
this value can be altered over time using the curve. The start and end frames will
signify the frames in which the curve affects the flow.
The Mask node
The Mask node can be used to create shape masks by picking mask's data blocks in the
browse ID data block. These mask's data blocks can be created in the UV Image Editor
by choosing the Mask mode as the editing context, shown in following screenshot.
These masks, generated using the Mask node, can be used in the compositing flow
to modify the pixels inside or outside the mask shape.
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Chapter 3
The Bokeh Image node
The Bokeh Image node can be used to create a custom bokeh shape. This shape
can be connected to the Bokeh Blur node, which then uses this shape as the bokeh
shape, as shown in following screenshot:
The description of the node is as follows:
• Flaps control the number of sides of the bokeh shape
• Angle rotates the bokeh shape
• Rounding reduces the sharpness at the corners of the sides
• Catadioptric creates and increases empty pixels from inside the bokeh shape
• Lens Shift adds a chromatic aberration effect to the shape, splitting the shape
with color offsets
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Working with Input and Output Nodes
Output nodes
Output nodes should be used to fetch data from the compositor and to view it in the
UV / Image Editor or save it as an image or image sequence. Different output nodes
are shown in following screenshot:
The Composite node
The Composite node connects the output of a composite flow to the renderer.
Connecting a node to the Composite node will output the result till the connected
node, when rendered. Leaving the Composite node unconnected will output a
blank image. Having multiple composite nodes might give unpredictable results.
The Image, Alpha, and Z input sockets store the corresponding connected results
into the respective image channels. The Z input can be used only if the EXR format
is chosen as the output format. This node can also be used to route the output to
the UV / Image Editor.
The Viewer node
The Viewer node is a handy tool to inspect the compositing flow. Using this node,
the output can be tunneled to backdrop of the Node Editor or the UV / Image Editor.
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Chapter 3
The Split Viewer node
The Split Viewer node allows you to inspect two images or two parts of the
compositing flow. Clicking on X will display a side-by-side comparison and
clicking on Y will display a top-down comparison. The image connected to the
top socket is displayed either on the right or on top of the window. The slider
provides an adjustment to the location of the split between the two sockets in
the viewer.
The File Output node
The File Output node can simulate AOVs (arbitrary output values) from the
compositing flow, similar to rendering passes from a render layer. Connecting
this node to any other node will write an image from the calculations done till
the connected node.
The Levels node
Connecting the Levels node to an image can output the value of a selected
component of the image. Combined RGB, Red, Green, Blue, or Luminance
channels can be read from the connected image. It can output mean/average
values or a standard deviation, which measures the diversity of values.
This chapter covered different ways to get data in and out of Blender
Compositor. This essentially forms the head and tail of the compositing flow.
The next chapter will demonstrate image manipulation techniques using
various Blender Compositor nodes.
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Image Manipulation
This chapter explains the different image manipulation nodes and their utilization
procedures that are available in Blender Compositor. These nodes play a major role
in attaining the desired look. The following is a list of topics covered in this chapter:
• The Bright/Contrast node
• The Hue Saturation Value node
• The Color Correction node
• Significance of Gain, Gamma, and Lift
• Significance of Midtones, Highlights, and Shadows
• The RGB Curves node
• The Color Balance node
• The Mix node
• The Gamma node
• The Invert node
• The Hue Correct node
• Transformation nodes
Image Manipulation Techniques
Understanding image manipulation
Image manipulation is the main phase for establishing a predetermined look in
compositing. This stage mostly involves grading, merging, transforming, and resizing
of the footage to achieve the desired look of the film. Blender Compositor is equipped
with various tool nodes to perform these tasks.
The Bright/Contrast node
The brightness of an image signifies the amount of light that is reflecting or radiating
from it. Increasing or decreasing the brightness of a node proportionally changes the
light reflection intensities of the input image as shown in following screenshot:
The contrast of an image signifies the luminance and/or color variation;
in other words, the separation between the darkest and brightest areas of the image.
Increasing the contrast emphasizes the distance between the dark and bright pixels
in the image, thus making shadows darker and highlights brighter. This effect makes
parts of the image pop up, making it a vibrant image. Decreasing the contrast makes
the shadows lighter and highlights darker, making the image dull and less interesting.
The following screenshot shows the effect of increasing and decreasing the contrast
value on the Bright/Contrast node:
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Chapter 4
The Hue Saturation Value node
The Hue Saturation Value node provides a visual spectrum-based image control.
The input image can be modified using the hue shift, which ranges from red
to violet.
Using the Hue slider, the image hue can be shifted in the visible spectrum range.
At the default value of 0.5, the hue doesn't affect the image. Reducing the value
from 0.5 to 0 adds more cyan to the image, and increasing the value from 0.5 to 1
adds more reds and greens.
Saturation alters the strength of a hue tone in the image. A value of 0 removes the hue
tones, making the image greyscale. A value of 2 doubles the strength of the hue tones.
Modifying Value affects the luminance of the color in the image. Increasing Value
makes an image lighter, and decreasing Value makes the image darker.
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Image Manipulation Techniques
Factor (Fac) determines how much this node affects the image. A factor of 0 means
that the input image is not affected by this node.
The following screenshot shows how Hue, Saturation, and Value will affect the
input image:
The Color Correction node
The Color Correction node provides three dimensional controls on the input image
as shown in following screenshot. As the first dimension, all vertical columns
provide control on Saturation, Contrast, Gamma, Gain, and Lift. As the second
dimension, all horizontal rows provide control on Master, Highlights, Midtones,
and Shadows. The third dimensional control is Red, Green, and Blue. This node
provides numerous combinations to arrive at a desired result through the use
of these three dimensional controls.
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Chapter 4
Master, Highlights, Midtones, and Shadows
The tonal information of the image can be divided into Shadows, Midtones,
and Highlights. As shown in the following screenshot, this information can be
represented as a histogram. In this representation, the left-hand values relate to
the dark tones (Shadows), the middle values relate to Midtones, and the right-hand
values relate to Highlights.
The Midtones Start and Midtones End sliders of the Color Correction node provide
flexibility to alter the range between Shadows, Midtones, and Highlights using
the luminance of the input image. These sliders don't consider the Red, Green,
and Blue checkboxes. Controlling the tonal information through the Master
attributes influences the complete range in the histogram curve of the image,
thereby affecting the whole image.
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Image Manipulation Techniques
This level of control can be extended to individual red (R), green (G), blue (B),
and luminance (L) channels of the image to gain more precision. The following
screenshot displays histograms of the individual channels:
Gamma, Gain, and Lift
To arrive at a desired result quicker when using a Color Correction node,
understanding the difference in control between Gamma, Gain, and Lift is vital.
These terms can be understood better using an input (x axis) versus output (y axis)
plot, as seen in following screenshot:
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Chapter 4
Each of these three properties controls the specific tonal information of an image,
summarized as follows:
• Gamma: This property controls the curve exponent, affecting the
midtones of an image
• Gain: This property controls the curve slope, mostly influencing the
image highlights
• Lift: This property controls the curve offset, mostly influencing the
image shadows
Mask socket
The Mask socket, also available for many other nodes, can be used to plug a grayscale
map to specify the node influence on the output. Node influence will be 100 percent at
value 1.
The RGB Curves node
The RGB Curves node provides a Bezier-curve-based control for image grading.
This curve represents an input (x axis) versus output (y axis) plot. Modifying this
curve remaps the output range, thereby providing a grading effect. This node also
provides controls to set up black and white levels for the input image.
A flat image that has all pixel values in the midtones range can be graded to
redistribute the pixel values to occupy the complete range of shadows, midtones,
and highlights. This makes the image more vibrant and interesting. An example of this
grading is shown in the following screenshot. The waveforms and histograms of both
the images show the redistribution of pixel values to occupy the complete range and
provide a better graded image.
Grading with this node can be done using Bezier curve or by tweaking the black
and white levels. An appropriate technique can be adapted based on the task.
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Image Manipulation Techniques
Grading by setting the black and white levels
The variation between the black and white levels of an image signifies its contrast.
Using the RGB Curves node to increase an image's contrast, instead of using a
Bright/Contrast node, gives the advantage of picking samples from the input image,
The darkest and the brightest levels of the input image can be picked as black and
white levels respectively, as shown in following screenshot. You can pick a sample
using the selector that pops up below the color wheel when either Black Level or
White Level is clicked on.
This method not only alters the contrast but also changes hue tones. This change can
be nullified by desaturating the black and white levels to zero using the saturation
(S) slider in the HSV mode. The following screenshot shows a change in contrast
without hue shifting:
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Chapter 4
Alternatively, the black and white levels can be adjusted directly using the HSV
or RGB mode in the color wheel that pops up when the small colored rectangular
region to the left of Black Level or White Level is clicked on.
Grading can be performed on individual red, green, and blue channels
by using the R, G, and B switches on the top left of the RGB Curves
node. This method provides more precision to achieve better grading.
Grading using the Bezier curve
A similar result, that was achieved in the previous technique, can be achieved
by using the Bezier curve. The bottom-left corner (0,0) in the plot is the shadows
point. The top-right corner (1,1) in the plot is the highlights point. All points that
lie in between these two points signify the midtones. The following screenshot
demonstrates grading using the Bezier curve to arrive at a similar result,
as achieved using the black and white levels technique:
The factor value (Fac) in this node represents the influence of this node on the output.
An image can be connected to this socket to specify node influence. A value of 1 will
display an influence of 100 percent in the output.
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Image Manipulation Techniques
The following screenshot specifies a few common grading effects—invert, posterize,
lighten, and contrast—performed using the RGB Curves node:
When using the RGB Curves node, we will sometimes need higher precision in
adjusting the curve points. The default setup makes it tedious to have such precision.
This task can be accomplished by having cascaded RGB Curves nodes with different
factor values as shown in following screenshot. In the following flow, first grade node
with Fac value of 0.25 provides four times higher precision for adjusting shadows,
second grade node with Fac value of 0.5 provides twice the precision for highlights,
and third grade node with Fac value of 1 provides default precision for midtones.
A similar flow can be created to have different precisions for R, G, and B channels.
The Color Balance node
The Color Balance node provides a control that is similar to the RGB Curves
node for grading, as shown in following screenshot. The difference is that since
this node has a color wheel for each of the Gain/Gamma/Lift components, its easier
to manage color-based grading. The same process in the RGB Curves node would
be a bit complicated since curves have to be shaped separately for R, G, and B.
However, having a curve-based control in the RGB Curves node provides more
precision in grading in comparison to the Color Balance node.
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Chapter 4
The Color Balance and RGB Curves nodes can be used in combination to make
flows to have the desired grading control.
The Mix node
The Mix node blends a base image connected to the top image socket with a second
image connected to the bottom image socket based on the selected blending modes,
as shown in following screenshot. All individual pixels are mixed based on the mode
selected in this node. The Alpha and Z channels are also mixed.
The output resolution of a Mix node will be the same as the
background node resolution.
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Image Manipulation Techniques
Blending modes
• Mix: In this mode, by using the alpha values, the foreground pixels are
placed over the background pixels.
• Add (A+B): In this mode, the pixels from both images are added.
• Subtract (A-B): In this mode, the pixels from the foreground are subtracted
from the background.
• Multiply (A*B): This mode results in a darker output than either pixel in
most cases (the exception is if any of them is white). This works in a similar
way to conventional math multiplication. The behavior is opposite to the
Screen mode.
• Screen [1-(1-A)*(1-B)]: In this mode, both images' pixel values are
inverted and multiplied by each other and then the result is again
inverted. This outputs a brighter result compared to both input pixels in
many cases (except if one of the pixels is black). Black pixels do not change
the background pixels at all (and vice versa); similarly, white pixels give
a white output. This behavior is the opposite of the Multiply mode.
• Overlay {If A<=0.5, then (2*A)*B, else 1-[1-2*(A-0.5)]*(1-B)}: This mode
is a combination of the Screen and Multiply modes, and is based on the
base color.
• Divide (A/B): In this mode, the background pixels are divided by
the foreground pixels. If the foreground is white, the background isn't
changed. The darker the foreground, the brighter is the output [division by
0.5 (median gray) is the same as multiplication by 2.0]. If the foreground is
black, Blender doesn't alter the background pixels.
• Difference: In this mode, both images are subtracted from one another
and the absolute value is displayed as the output. The output value shows
the distance between both images: black stands for equal colors and white
for opposite colors. The result looks a bit strange in many cases. This mode
can be used to compare two images, and results in black if they are equal.
This mode can also be used to invert the pixels of the base image.
• Darken [Min (A, B)]: This mode results in a smaller pixel value by comparing
both image pixels. A completely white pixel does not affect the background
at all and a completely black pixel gives a black result.
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Chapter 4
• Lighten [Max (A, B)]: This mode results in a higher pixel value by comparing
both image pixels. A completely black pixel does not alter the image at all and
a completely white pixel gives a white result.
• Dodge [A/(1-B)]: This mode brightens the image by using the gradient in the
other image. It outputs lighter areas of the image where the gradient is whiter.
• Burn [1-(1-A)/B]: This mode darkens one socket image on the gradient fed
to the other image. It outputs darker images.
• Color: In this mode, each pixel is added with its color tint. This can be used
to increase the tint of the image.
• Value: In this mode, the RGB values from both images are converted to HSV
parameters. Both the pixel values are blended, and the hue and saturation of
the base image are combined with the blended value and converted to RGB.
• Saturation: In this mode, the RGB values of both images are converted to
HSV parameters. Both pixels saturations are blended, and the hue and value
of the base image are combined with the blended saturation and converted
to RGB.
• Hue: In this mode, the RGB parameters of both pixels are converted to HSV
parameters. Both pixels hues are blended, and the value and saturation of
the base image are combined with the blended hue and converted to RGB.
Use Alpha
The Use Alpha button of the Mix node instructs the Mix node to use the Alpha
channel available in the foreground image. Based on the grayscale information
in the alpha channel, the foreground pixels are made transparent to view the
background image. The effect of the selected blending mode is thus seen only
in the nontransparent foreground pixels. The Alpha channel of the output image
is not affected by this option.
The factor input field (Fac) decides the amount of mixing of the bottom socket.
A factor of 0.0 does not use the bottom socket, whereas a value of 1.0 makes full
use. In Mix mode, 50:50 (0.50) is an even mix between the two, but in Add mode,
0.50 means that only half of the second socket's influence will be applied.
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Image Manipulation Techniques
The following screenshot shows outputs from all the described Mix modes without
altering the inputs connected to the top and bottom nodes:
The Gamma node
An overall gamma correction can be made to the final result using the Gamma
node. This correction helps to alter the lighting information in the result.
The gamma value in this node is the gamma correction value.
Gamma correction = 1/gamma.
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Chapter 4
The Invert node
The Invert node can invert the pixel values in the RGB or Alpha channel based on
what is selected in the node. This node comes in handy during masking to invert
the alpha channel.
The Hue Correct node
The Hue Correct node is very useful in that it provides unique control to be able
to raise or lower the hue, saturation, and value over the visible color spectrum.
The following set of screenshots shows the different effects obtained using similar
curves in the S and V tabs:
[ 47 ]
Image Manipulation Techniques
Transformation tools
Transformation tools are used to reposition, reorient, or resize the input footage.
Blender is equipped with the Rotate, Translate, Scale, Flip, Crop, and Transform
nodes as transformation tools. The following screenshot explains the Rotate,
Translate, and Scale nodes:
The following screenshot explains the effect of using the Flip node's modes Flip X,
Flip Y, and Flip X & Y:
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Chapter 4
The following screenshot explains how the Crop node can be used to modify
an image's boundaries:
The following screenshot explains how to use the Transform node to reposition
or reorient an image:
This chapter explained the multiple techniques that can be used as per your
requirements to give a predetermined or desired look to an image.
The next chapter deals with some advanced techniques that are beyond image
manipulation in order to make an image look more believable, including various
camera effects.
[ 49 ]
Beyond Grading
This chapter deals with advanced compositing beyond grading. These techniques
emphasize alternate methods in Blender Compositing for some specific 3D render
requirements that can save lots of render time, thereby also saving budgets,
in making a CG film. Following is the list of contents that will be presented
in this chapter:
Fresnel effect in compositing
Depth of Field and Bokeh
Motion and directional blur
Lens distortions
UV mapping
Organizing nodes
As the final look of the frame is achieved during the compositing stage, there will
always be numerous occasions where there is a requirement for more render passes
to finalize the image. This results in extra 3D renders, along with more time and
money. Also, few inevitable applications that give life to an image, such as lens
effects (Defocus, Glares, and motions blur), are render intensive. Blender Compositor
provides alternate procedures for these effects, without having to go back to 3D
renders. A well planned CG pipeline can always provide sufficient data to be able
to use these techniques during the compositing stage.
Beyond Grading
Relighting is a compositing technique that is used to add extra light information
not existing in the received 3D render information. This process facilitates additional
creative tweaks in compositing. Though this technique can only provide light without
considering shadowing information, additional procedures can provide a convincing
approach to this limitation.
The Normal node
Relighting in Blender can be performed using the Normal node. The following
screenshot shows the relighting workflow to add a cool light from the right screen.
The following illustration uses a Hue Saturation Value node to attain the fake light
color. Alternatively, any grading nodes can be used for similar effect. The technique
is to use the Dot output of the Normal node as the factor input for any grade node.
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Chapter 5
The following screenshot shows relighting with a cyan color light from the top using
the Normal node:
The light direction can be modified by left-clicking and dragging on the diffused
sphere thumbnail image provided on the node.
This fake lighting works great when used as secondary light highlights. However, as
seen on the vertical brick in the preceding screenshot, light leaks can be encountered
as shadowing is not considered. This can often spoil the fun. A quick fix for this is to
use the Ambient Occlusion information to occlude the unwanted areas.
The following screenshot illustrates the workflow of using the Ambient Occlusion
pass along with the normal pass to resolve the light leak issue. The technique is to
multiply the dot output of the Normal node with Ambient Occlusion info from the
rendered image using Mix or Math nodes. As it can be observed in the following
screenshot, the blue light leaks on the inside parts of the vertical brick is minimized
by the Ambient Occlusion information. This solution works as long as relighting is
not the primary lighting for the scene.
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Beyond Grading
Another issue that can be encountered while using the Normal node is negative
values. These values will affect the nonlight areas, leading to an unwanted effect.
The procedure to curb these unwanted values is to clamp them from the Dot output
of the Normal node to zero, before using as a mask input to grade nodes.
The following screenshot illustrates the issue with negative values. All pixels that
have an over-saturated orange color are a result of negative values.
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Chapter 5
The following screenshot shows the workflow to clamp the negative values from the
dot information of a normal pass. A map value is connected between the grade node
and Normal node, with the Use Minimum option on. This makes sure that only
negative values are clamped to zero and all other values are unchanged.
The Fresnel effect
The Fresnel option available in shader parameters is used to modify the reflection
intensity, based on the viewing angle, to simulate a metallic behavior. After 3D
rendering, altering this property requires rerendering. Blender provides an alternate
method to build and modify the Fresnel effect in compositing, using the Normal node.
The following screenshot illustrates the Fresnel workflow. In this procedure, the dot
output of a Normal node is connected to the Map Range node and the To Min /
To Max values are tweaked to obtain a black-and-white mask map, as shown in the
screenshot. A Math node is connected to this mask input to clamp information to the
0-1 range.
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Beyond Grading
The 3D-combined render output is rebuilt using the diffuse, specular, and reflection
passes from the 3D render. While rebuilding, the mask created using the Normal
node should be applied as a mask to the factor input of the reflection Add node.
This results in applying reflection only to the white areas of the mask, thereby
exhibiting the Fresnel effect. A similar technique can be used to add edge
highlights, using the mask as a factor input to the grade nodes.
Depth of Field
Depth of Field (DOF) is the simulation of lens focus on the subject of the scene.
This effect emphasizes on the subject by blurring everything ahead and behind
the subject. In the blurred region, all the tiny highlights expand to exhibit shapes
called Bokeh.
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Chapter 5
The Defocus node
Blender provides a Defocus node to simulate DOF. The following screenshot depicts
the result of the DOF application as a postprocess in Blender Compositor. From the
following screenshot, it can be observed that the emphasis is on the red block,
blurring the other blocks and simulating the focus effect. This node requires
an image and corresponding Z Depth inputs.
The Bokeh type
The Bokeh type can be set to modify the shape of the Bokeh, emulating a circle,
triangle, square, pentagon, hexagon, heptagon, or octagon. Beyond octagon, there
will not be any significant difference, as compared to the circle mode. The following
screenshot shows different Bokeh shapes on the blue block:
Angle adds a rotational offset, in degrees, to the chosen Bokeh shape.
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Beyond Grading
Gamma correct
Gamma correct accentuates the Bokeh shape by brightening the out-of-focus areas
of the image.
FStop is a very important parameter that gives control over the focal blur amount.
FStop simulates the aperture in a real lens, preserving the luminosity of the image.
Similar to a real camera, the smaller the FStop number, the higher the lens iris
opening time, and the shallower the Depth of Field. At a default value of 128,
everything is in perfect focus, which is assumed as infinity. Half of this value will
double the blur amount. This button is available only when enabling Use Z Buffer.
Maxblur limits the blur amount of the most out-of-focus regions of the image.
Since the Defocus node gets slower to process as the blur amount increases, this
value helps limit the maximum blur radius allowed. With a default value of zero,
there will not be any limit to the maximum blur amount.
When an object that is in-focus overlaps a very far defocused background, aliased
edges can be observed. The number of artifacts increases with the increase in
distance between the overlapped objects. This value can be used to set how large
that blur difference can be, to consider it safe and thereby prevent the occurrence
of aliased edges.
The Preview mode calculates the result a lot faster compared to the Normal mode,
using a limited number of (quasi) random samples. This mode also introduces
grain, which is the noise in the image (though the noise reduces with more
samples). This option should be disabled before rendering.
Use Z-buffer
Enabling the Use Z-Buffer option uses the focal point set in the render camera
of the 3D Blender scene, as shown in following screenshot. Enabling this option
disables Z-Scale.
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Chapter 5
Using Z-Scale, focus points can me manually adjusted to the required object in
the image.
The Bilateral Blur node
The Bilateral Blur node implements a high quality adaptive blur on the source
footage. This node can be used to soften a grainy ray-traced Ambient Occlusion
pass, smoothing the output from various unbiased renderers. Many heavy
performance effects, such as blurry refractions, reflections, and soft shadows
can be attained with this node. Its components are as follows:
• Image: This is the input image that is to be blurred.
• Determinator: This is a source that defines the edges/borders for the
blur in the image.
• Iterations: This specifies how many times the filter will perform the
operation on the image. This actually defines the radius of the blur.
• Color Sigma: This specifies the threshold for which the differences of
color in the image should be considered as edges.
• Space Sigma: This is a fine-tuning variable for the blur radius.
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Beyond Grading
The following screenshot illustrates its application to smoothen a rendered shadow's
information without blurring the object shape, by routing the Depth and Normal
data to the determinator:
The Blur node
The Blur node can be used as an alternate and fast solution to defocus an image;
the effect will not be as appealing as the Defocus node though. Using one of
the seven blur modes, this node adds blur to the image, as shown in following
screenshot. The radius of the blur is defined by the X and Y number buttons.
Blur is perceived on the image when a value higher than the default zero is used.
The Size input node can restrict the blur radius as a mask. The values must be
mapped between the range of 0-1, as they will be multiplied with the X and Y
number button values.
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Chapter 5
The X and Y values signify the number of pixels over which the blur effect can spread.
The Bokeh button will force the blur node to use a circular blur filter. This node
gives a higher quality output, but with higher render times when using the Bokeh
option. Enabling Gamma does gamma correction on the image before blurring it.
Different blur effects can be achieved using different filter types that can be chosen
as per the requirement. The following is a list of the types of filter, followed by a
screenshot illustrating the blur types:
• Flat: This shows everything as uniformly blurred
• Tent: This performs a linear falloff by preserving the high and the lows better
• Quadratic and Catrom: These makes the sharp-contrast edges crisp
• Cubic and Mitch: These preserve the highs but give an almost
out-of-focus blur while softening sharp edges
Optical distortions
Every camera lens is bound to have a level of error in it. This leads to luminance drops
and patterns such as lens flares, glares, and chromatic aberrations. Some lenses are
used to capture images with distorted or enhanced perspectives, such as the fish eye
lens and spherical lens. Adding these effects to a CG image will enhance the realism
of it. Blender provides a very wide range of nodes to achieve these distortions.
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Beyond Grading
The Glare node
Glare is a discomfort of vision in the presence of a bright source of light. This is
seen in any photograph with a light source in its content. This phenomenon exhibits
streaks, discs, or foggy rays shooting away from the source. Adding these effects
adds realism to the image.
Blender's Glare node provides multiple options to simulate this behavior.
The following screenshot illustrates the four types of glares available in
Blender's Glare node:
The Lens Distortion node
The Lens Distortion node provides perspective alteration procedures with a
chromatic aberration effect, that is, a distortion due to failure of the lens to focus
all colors to the same convergence point.
• Distort: This can be used to alter the perspective. This value is 0 by
default. Increasing this value can lead to perspective distortion.
• Dispersion: This can be used to simulate a chromatic aberration effect.
This value is 0 by default. Increasing this value begins to show disparity
of colors in the edges of the objects/pattern in the image.
• Jitter: When enabled, this introduces grain to the image, simulating loss
of luminance from lens.
• Fit: This can be used to fit the distorted image to a size that covers the empty
pixels created due to distortion. Since this resizes the pixels to fit within the
resolution, a higher distortion value can show a pixelated image.
[ 62 ]
Chapter 5
All these options can be used in cohesion to obtain multiple lens distortion effects,
thus simulating a real world lens and adding more realism to the image.
The following screenshot illustrates the effects that can be obtained using this node.
Observe the black/empty pixels created at the bottom corners due to distortion of
the perspective.
The Despeckle node
The Despeckle node simulates an effect of shattering the pixels. Threshold can
be used to limit the effect based on the luminance of the image. Alternatively,
a gray-scale image can be connected to factor input to control the effect of the
Despeckle node, as shown in the following screenshot:
[ 63 ]
Beyond Grading
The Filter node
The Filter node implements various image enhancement filters, producing a variety
of image distortion effects. The following is a list of filter types available in this node,
followed with a screenshot:
• Soften: This blurs the image slightly
• Sharpen: This increases the contrast, especially at the edges
• Laplace: This softens the edges
• Sobel: This creates a negative image that highlights the edges
• Prewitt: This tries to do what Sobel does, but goes one step better
• Kirsch: This is the same as Prewitt or Sobel but gives a better blending
on the edges
• Shadow: This performs a relief emboss/bump map effect, darkening the
outside edges
[ 64 ]
Chapter 5
Motion blur
Motion blur is the streaky blur that follows the direction of objects in a motion
relative to the camera movement. This is due to long exposure or object/camera
rapid motion. Adding this simulation to the composite image also adds realism.
The Vector Blur node
The Vector Blur node in Blender provides an effective motion blur solution in
compositing. This node requires vector data and depth data connected to Speed
and Z, respectively.
Transform information of a specific point travelled in relation to
the previous and next frames is stored as a vector pass, also called
Motion Vectors.
The following is list of the Vector Blur node attributes:
• Samples: This defines the quality of the blur
• Blur: This specifies the amount of the blur in pixels
• Min: This is the threshold for the slowest moving points of the image
• Max: This is the threshold for the fastest moving points of the image
The following screenshot illustrates Motion Blur, simulated using the Vector
Blur node:
[ 65 ]
Beyond Grading
The Directional Blur node
The Directional Blur node can be used to create a fake motion blur effect by blurring an
image in a specified direction and magnitude. This can be used as a faster solution for
Vector Blur, in specific cases. Since this is a fake blur, it blurs all points on the image,
without considering the movement of the points. Its parameters are as follows:
• Iterations: This controls the number of times the image is duplicated
to create the blur effect. Higher values give smoother results.
• Wrap: This wraps the image on the x and y axis to fill in areas that
become transparent from the blur effect.
• Center: This sets the position for the blur center. It makes a difference
if Angle, Spin, and/or Zoom options are used.
• Distance: This regulates the largeness of the blur effect.
• Angle: This blurs the image at the angle specified from the center.
• Spin: This rotates the image at each iteration to create a spin effect from
the center point.
• Zoom: This scales the image at each iteration, creating the effect of a zoom.
The following screenshot illustrates the utilization of the Directional Blur node.
It can be observed that all the spheres are now blurred in a specified direction,
unlike in Vector Blur, where only the center sphere was in motion. In many rapid
motion scenes in which the scene subjects are far from the camera, this effect can
give a believable and faster result.
Texture mapping
Texture mapping in compositing is yet another time-saving technique that facilitates
in wrapping a texture to a mesh. The UV pass, as a 32-bit float image, is required to
perform this wrapping.
[ 66 ]
Chapter 5
The Map UV node
The Map UV node in Blender should be used to perform texture mapping at the
compositing stage.
As illustrated in the following screenshot, a Texture and UV Pass have to be connected
to the respective sockets of the Map UV node to attain the wrapping. As seen in the
following example, the sphere and plane rendered without any textures are wrapped
with a texture using a map UV node.
This technique allows the user to be able to modify specific object textures in
compositing without needing a 3D rerendering. This can save a huge amount
of time in the CG film production process, where creative changes are bound
to happen at any stage.
Organizing plays a major role in CG production. It can increase efficiency by gaining
consistency. Organizing the master flows (flows done for a few typical shots that will
be replicated on similar shots after getting the director's approval) will make it easy to
replicate or reuse them for other shots. This also reduces confusion when relooking at
the flow over a period of time. Blender provides the following methods to organize
the flow.
[ 67 ]
Beyond Grading
Grouping is a method of gathering a node network and converting it to one
node. This group can be reused any number of times with the same functionality.
This also makes the flow less cumbersome.
Ctrl + G is the shortcut key for grouping a selected node network
Alt + G is the shortcut key for ungrouping
In the following screenshot, the relighting network built to create a fake top blue
light can be selected and grouped. Clicking on the link icon on the top right of the
group node will open the network inside the group with a pale green backdrop.
Clicking on the Go to parent node tree icon, as shown in following screenshot,
will switch back to the actual node network. Alternatively, the Tab key can be
used to switch in and out of group levels. Multiple levels of groupings can be
made to form nested groups.
The group can be renamed by selecting the group node; press N to open the Properties
window and modify the name under node name, as shown in following screenshot.
All groups of the current file can be found by navigating to the Add | Group menu.
[ 68 ]
Chapter 5
The input and output sockets can be renamed in the properties panel, accessed by
the N key, as shown in the following screenshot:
The Layout options in Blender Compositor allow the user to discriminate and
define parts of the flow, thus increasing the readability and understanding of
the flow significance. The Add | Layout menu item displays the layout options
available in Blender.
[ 69 ]
Beyond Grading
As shown in the following screenshot, Frame can be added as a backdrop to a group
of nodes to add a note, specifying the significance of the network. Each frame can be
given a specific color to emphasize the significance. Notes can be added in the Label
textbox under the Properties panel of the frame. Similarly, the frame color can be
modified in the Color Presets textbox.
[ 70 ]
Chapter 5
Often, the nodes will overlap the noodle connections or overlapping connections,
making things confusing. Using Reroute, the connections can be organized.
Left-clicking on a noodle with the Shift key pressed on the keyboard will also
add the Reroute node.
Switch can be used in specific cases where a portion of the network needs to be
bypassed, but doesn't need to be deleted from the flow.
This chapter dealt with several advanced techniques, such as Motion blur, Defocus,
optical distortions, and UV mapping, that can save project time. This chapter also
described efficient ways of organizing the flow for reuse or sharing, boosting
efficiency to hit the targets.
The next chapter will illustrate masking, keying, and filtering techniques.
[ 71 ]
Alpha Sports
This chapter starts by providing an understanding of the significance of an alpha
channel and some issues related to it. After realizing the alpha channel, this chapter
deals with different keying and masking techniques. Following is the list of topics
covered in this chapter:
• Significance of the alpha channel
• Blender's alpha modes
• Layering concept and formula
• Using the alpha channel when layering the foreground over the
background with the Mix and Alpha Over nodes
• Solving fringing issues while using the alpha channel with the Mix
and Alpha Over nodes
• Generating matte masks using the ID Mask node
• Different ways to invert matte information
• Edge filtering
• Value and luminance
• Concept of keying and what to inspect in the footage to be keyed
• Understanding Blender's keying nodes
Alpha Sports
What is an Alpha channel?
The alpha channel first introduced by Alvy Ray Smith in the 1970s, can store
values between 0-1, signifying whether a specific pixel is transparent, opaque,
or semitransparent. Though this channel is boring to look at, this information
is very essential when merging footages. Alpha information can be stored either
independent of RGB, referred to as straight alpha, or by multiplying it with RGB,
referred to as premultiplied alpha. A value of zero in the alpha channels signifies
that the RGB pixel should be completely transparent, and opaque when the value
is one. The following screenshot portrays an alpha channel:
Alpha modes in Blender
As shown in the following screenshot, Blender has two alpha modes. The Transparent
mode considers transparency parameters in shaders and accordingly generates the
pixel value for alpha. The Sky mode considers sky as opaque, thereby making the
alpha channel completely white.
[ 74 ]
Chapter 6
The following screenshot represents alpha, rendered with the Sky Mode:
The following screenshot represents alpha, rendered with the Transparency mode:
Visualizing alpha in Blender
Blender provides three different drawing modes to view alpha with respect to
the image RGB channel. As shown in the following screenshot, these options can
be seen in the menu panel of the UV/Image Editor. The RGB * A mode displays
RGB with premultiplied alpha, the RGB mode displays only RGB information,
and the A mode displays only alpha channel information in the image.
[ 75 ]
Alpha Sports
The RGB mode draws the RGB channel with "aliased" edges, since it doesn't consider the
alpha channel.
Significance of alpha in the layering
The layering concept involves merging more than one piece of footage based on the
color, blending modes, or the transparency of the individual footage. In either of the
cases, one of the pieces of footages behaves as the foreground and the other behaves
as the background. After introducing the alpha channel, the background information
perceived can be based on the alpha values. The following screenshot shows the
layering of a foreground and background using the alpha channel. This technique
is vital for merging the CG elements into live shot footage.
[ 76 ]
Chapter 6
Following is the layering formula used in the type of layering we just discussed:
(FG * A) + (BG(1- A)) = Result, where FG stands for the foreground
image, BG stands for the background image, and A stands for FG Alpha.
Layering in Blender with the alpha
To perform layering in Blender Compositing, the alpha channel can be used either
with the Mix node or Alpha Over node.
Layering with the Mix node
The following screenshot depicts the process of layering using a Mix node.
A background image is connected to the upper Image socket and a foreground
image to the lower Image socket of the Mix node. Now the result shows only the
aliased RGB channel of the foreground. If the foreground image has an alpha
channel associated, then Include Alpha Toggle should be used in the Mix node,
as shown in following screenshot:
[ 77 ]
Alpha Sports
If the foreground image doesn't have the alpha channel, then a separate alpha image
can be fed to the Fac socket of the Mix node to obtain the same result. Alternatively,
if the combined channel is accessible, then a Separate RGBA converter node can be
used to extract the alpha channel from the combined pass information and can be fed
to the Fac input of the Mix node, as shown in the following screenshot:
Layering with the Alpha Over node
Layering using the Alpha Over node can be performed by connecting a background
image to the upper Image socket and a foreground image to the lower Image socket
of the Alpha Over node, as shown in the following screenshot:
[ 78 ]
Chapter 6
Fringe issue
When the resulting images from the Alpha Over and Mix layering techniques are
compared, a one-pixel dark line can be seen on the edge of the foreground content
in the Mix layering mode, but not seen in Alpha Over process. This is termed as
Fringe issue, as shown in the following screenshot:
At first, it might seem that the Mix node is messy, but this difference is due to
the way both the nodes assume whether the alpha input is premultiplied or
straight. When using the transparent alpha mode, Blender renders the image
with a premultiplied alpha. Since the Alpha Over node assumes that the input
is premultiplied by default, it performs calculations correctly. However, the Mix
node assumes that the input has a straight alpha.
To solve the issue, an Alpha Convert node should be connected to the lower Image
socket of the Mix node. By selecting the Premul to Straight mode in the Alpha Convert
node, the straight alpha mode is created from premultiplied alpha input. When this is
fed to the Mix node, this fringe issue is resolved.
[ 79 ]
Alpha Sports
The following screenshot represents the use of the Alpha Convert node to solve the
fringe issue for a Mix node, with the transparent alpha mode being used:
Generating mattes using the ID Mask
There will be many instances during CG compositing where a few specific meshes
in the image would require a mask pass. This provides control to modify specific
pixels. To obtain these mattes, the ID Mask node can be used along with the
information stored in Object Index or Material Index passes.
When given a value for the index, the ID Mask node creates a mask for the meshes
that have the same value assigned as their Pass Index value, as shown in the following
screenshot. All these Pass Index values of meshes can be obtained using the Object
Index pass. The Object or Material Index pass has to be connected to the ID value
socket of the ID Mask node, for the node to pick the Index values. The generated
mask information can be used as an input for the Fac sockets available to many
Blender nodes to affect only the required mesh.
[ 80 ]
Chapter 6
In the following screenshot, assigning Pass Index to one of the three cubes and
enabling the Object Index pass is explained. When the Object Index pass from this
example is plugged into the ID value socket of the ID Mask node and a value of 2 is
given as the index value to the ID Mask node, it outputs the mask of the blue cube.
The following screenshot shows how the blue cube mask is created using the
ID Mask node, using the Object Index pass:
[ 81 ]
Alpha Sports
Now that the mask for the blue cube is available, this blue cube can be converted
to a pale and bright colored cube, with the flow explained in following screenshot:
Similar to Object Index, Material Index can also be used with the ID Mask node.
Material Index is available in the Material option.
Edge filtering
Sometimes, the edges of the alpha need to be expanded or blurred to obtain a specific
effect or to soften the aliased edges. This effect can be achieved using the Blur and
ColorRamp nodes in cohesion.
To blur the mask generated for the blue cube, it has to be connected to a Blur node and
the Blur node has to be connected to the ColorRamp node, as shown in the following
screenshot. Now, by increasing the X and Y values in the Blur node, the mask area can
be expanded or contracted. Using the black and white handles in the ColorRamp node,
the edge of the modified mask can be softened or sharpened. This process of altering
the mask boundary is termed as edge filtering.
[ 82 ]
Chapter 6
Inverting values
Sometimes, it's faster to invert a mask or RGB tones rather than recreating a new
one. Though there is an Invert node to do this, it's worth understanding how the
same effect can be obtained using a different node. This can enhance the perception
on node utilizations, as shown in the following screenshot:
The previous screenshot explains multiple ways to invert an image. Using the F key
on the ColorRamp node to invert the black and white handles, subtracting the input
from 1 using a Math node, and reversing the default curve in RGB curves node will
result in inverting the input image.
[ 83 ]
Alpha Sports
Keying, also known as chroma keying or color keying, is the process of converting
a specific range of colors into the alpha channel, to show the background footage
when layered. The following screenshot shows an example of this concept:
Value and luminance
A clear understanding of the differences between value and luminance is very
essential in compositing since the human eye is more sensitive to luminance than to
colors. It turns out to be even more crucial while keying, since everything in keying is
dependent on how you start the process, with respect to a specific channel in a specific
color space. To explain this in detail, the following screenshot will be used, which
contains different tones with at least one of the RGB components having a value of 1:
[ 84 ]
Chapter 6
The desaturation of an image will result in displaying the value of the image.
The value displays the maximum value in between the RGB components. Since the
input image has the value as 1 in any one of the RGB channels, the result will be a full
white image signifying a value of 1 in any of the colors, existing as the maximum value
in any of the channels.
When we see the colors, we can perceive perceive blue as dark color compared to
Cyan and Yellow as bright compared to red. This variation in brightness that we
perceive is called the luminance of the color.
Luminance of an image can be displayed using the RGB to BW node. The following
screenshot illustrates the luminance levels of colors when using the RGB to BW node:
[ 85 ]
Alpha Sports
It has to be understood that the desaturation of an image is not the same
as making it into a black-and-white image.
Luminance of the same image, when displayed as a Y channel in the Separate
YUVA node, also shows the variation of brightness in colors, as shown in the
following screenshot:
The following screenshot shows the luminance of the same image using three
different modes of the Separate YCbCrA node:
It can be observed that the luminance displayed in all these models is not the
same since the weightage of 100 percent for each channel in RGB is different in
each model. So, the model to be chosen depends on the requirement.
Y in YUVA is the same as Y in YCbCrA in the Jpeg mode
UV and CbCr are chrominance components that provide color information
[ 86 ]
Chapter 6
After having a good understanding of luminance and the different models available,
an apt model can be chosen as a starting point in keying, where the color ranges to
be keyed are close to blacks or whites in a specific color model.
Inspecting a green/blue screen footage
The success of keying green/blue screen footage depends on the following factors.
These have to be inspected before proceeding to keying.
• The color to be keyed should have consistent lighting
• The subjects should be far enough from the green/blue screen, to avoid
color spill
• The subjects should be lit properly
• The footage should be uncompressed
The Difference Key node
The Difference Key node creates a mask based on the difference between the inputs
plugged to the Image 1 and Image 2 sockets. Tolerance and Falloff can be adjusted
to fine-tune the created mask. The following screenshot shows an example using the
Difference Key node to modify the flower tone:
[ 87 ]
Alpha Sports
The Distance Key node
The Distance Key node works similar to the Difference Key node but with a different
algorithm. Tolerance and Falloff can be adjusted to fine-tune the created mask.
The Luminance Key node
The Luminance Key node creates a mask based on luminance of the input plugged
to the Image socket, controlled by Low and High handles. This node works as per the
YUVA color space. The following screenshot shows an example using the Luminance
Key node to modify the flower tone:
The Color Key node
The Color Key node creates a mask based on the sampled color in the key color area.
HSV sliders can be adjusted to the generated mask.
[ 88 ]
Chapter 6
The Channel Key node
The Channel Key node provides options to select any component in any color space
to start creating a mask. High and Low sliders can be used to modify the generated
mask as per the requirements. The following screenshot shows an example using
Key Channel to modify the flower tone:
This chapter explained the significance of the alpha channel and how to create
or manipulate alpha masks using Object Index and keying techniques. A very
important understanding about the difference between value and luminance
was also covered in this chapter.
Using all the different concepts and techniques explained in this book, many
complex Blender node trees related to VFX or CG animation can be created.
Based on the desired effect, a specific technique or a group of techniques
explained in this book can be applied.
[ 89 ]
visualizing 75
alpha channel
about 74
Premultiplied alpha 74
Straight alpha 74
alpha modes
sky 74
transparent 74
Alpha Over node
used, for layering 78
A mode 75
AOVs (arbitrary output values) 31
architecture, Blenders Compositor
node-based architecture 15
Bezier curve
used, for grading RGB Curves node 41
Bilateral Blur node, DOF 59
about 7
alpha modes 74
alpha, visualizing 75
color modes 8
color space 8
image color depth 8
image input/output system 8
Blender Compositor
about 15
architecture 15
color management 22
colr management 22
Depth of Field (DOF) 56
Fresnel effect 55
image manipulation 33
linear workspace 23
motion blur 65
optical distortions 61
organizing 67
relighting 52
shortcuts 24
texture mapping 66
UI 16, 17
blending modes, Mix node
about 44
add 44
burn 45
color 45
darken 44
difference 44
divide 44
dodge 45
hue 45
lighten 45
mix 44
multiply 44
overlay 44
saturation 45
screen 44
subtract 44
value 45
Blur node, DOF 60
Bokeh 56
Bokeh Image node 29
Bokeh Type 57
Bright/Contrast node 34
BW, color mode 8
CG compositing 6, 7
Channel Key node 89
chroma keying 84
Color Balance node 42, 43
Color Correction node
about 36
Gain 39
Gamma 39
Highlights 37
Lift 39
Mask socket 39
Master attributes 37
Midtones 37
Shadows 37
color keying 84
Color Key node 88
color management 22
color modes
BW 8
color space
about 8
HSV color space 9
RGB color space 9
YCbCr color space 10
YUV color space 9
Composite node 30
Defocus node, DOF
about 57
angle 57
Bokeh Type 57
FStop 58
Gamma correct 58
Maxblur 58
Preview mode 58
Threshold 58
Z-buffer, enabling 58
Z-Scale 59
Depth of Field (DOF)
about 12, 56
Bilateral Blur node 59
Blur node 60
Defocus node 57
Despeckle node 63
Difference Key node 87
directed acyclic graph (DAG) 15
Directional Blur node, motion blur 66
Distance Key node 88
edge filtering 82
Fac socket, Mix node 78
factor input field, Mix node 45
File output node 31
Filter node 64
Fresnel effect 55
Fresnel workflow 55
Fringe issue 79
FStop 58
Gain property, Color Correction node 39
gamma 22
Gamma correct 58
Gamma node 46
Gamma property, Color Correction node 39
Glare node 62
green/blue screen footage
inspecting 87
HSV color space 9
Hue Correct node 47
Hue Saturation Value node
about 35
factor 36
hue slider, using 35
saturation 35
value 35
[ 92 ]
Luminance Key node 88
value desaturation 85
Hue slider, Hue Saturation Value node 35
ID Mask node
used, for generating mattes 80-82
image color depth 8
image input/output system 8
image manipulation
about 34
Bright/Contrast node 34
Color Balance node 42
Color Correction node 36
gamma node 46
Hue Correct node 47
Hue Saturation Value node 35
Invert node 47
Mix node 43
RGB Curves node 39
transformation tools 48
Image node 27
Include Alpha Toggle 77
input nodes 16
about 25
Bokeh Image node 29
Image node 27
Mask node 28
Movie Clip node 27
Render Layers node 26
RGB node 27
Texture node 28
Time node 28
Value Node 27
Invert node 47
about 84
Channel Key node 89
Color Key node 88
Difference Key node 87
Distance Key node 88
green/blue screen footage, inspecting 87
luminance 84-86
Fringe issue 79
performing, with alpha channel 77
performing, with Alpha Over node 78
layering concept
about 76
alpha channel, used 76
layout options
about 69
frame 70
reroute 71
switch 71
Lens Distortion node 62
Levels node 31
Lift property, Color Correction node 39
linear workspace 23
luminance 85
Luminance Key node 88
Map UV node 67
Mask node 28
Mask socket, Color Correction node 39
generating, ID Mask node used 80-82
Maxblur 58
Mix node
about 43
blending modes 44
Fac socket 78
factor input field 45
Use Alpha button 45
used, for layering 77
motion blur
about 65
Directional Blur node 66
Vector Blur node 65
Motion Vectors 65
Movie Clip node 27
[ 93 ]
National Television System Committee
(NTSC) 9
node 15
node-based architecture 15
node editor 16-19
Normal node, relighting
using 52-55
optical distortions
about 61
Despeckle node 63
Filter node 64
Glare node 62
Lens Distortion node 62
about 67
grouping 68, 69
layout 69
output nodes 16
about 25, 30
Composite node 30
File Output node 31
Levels node 31
Split Viewer node 31
Viewer node 30
Phase Alternating Line (PAL) 9
Premultiplied alpha 74
about 52
Normal node, using 52
render layers 10
Render Layers node 26
render passes
about 10
AO 12
Color 12
Combined 11
Diffuse 12
Emit 12
Environment 12
Indirect 12
Material Index (IndexMA) 12
Mist 12
Normal 12
Object Index (IndexOB) 12
Reflection 12
Refraction 12
Shadow 12
significance 11, 13
Specular 12
UV 12
Vector 12
Z (Z depth) 12
RGB mode 8
RGBA mode 8
RGB color space 9
RGB Curves node
about 39
grading, Bezier curve used 41, 42
grading, by setting black and white levels
40, 41
RGB mode 75
RGB node 27
Separate YCbCrA node 86
Separate YUVA node 86
Sequential Color with Memory (SECAM) 9
shortcuts, Blenders Compositor 24
sky mode, alpha 74, 75
sockets 18
Split Viewer node 31
Straight alpha 74
Texture 67
texture mapping
about 66
Map UV node 67
Texture node 28
Threshold 58
Time node 28
[ 94 ]
transformation nodes 16
transformation tools 48, 49
transparent mode, alpha 74
UI, Blenders Compositor
node editor 18, 19
UV Image Editor 16, 20
Use Alpha button, Mix node 45
UV Image Editor 16, 20, 21
UV Pass 67
value desaturation 85
Value node 27
inverting 83
Vector Blur node, motion blur 65
Viewer node 30
YCbCr color space 10
YUV color space 9
enabling 58
using 59
[ 95 ]
Thank you for buying
Blender Compositing and Post Processing
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No programming or scripting required
Blender 2.5 Character Animation
ISBN: 978-1-84951-320-3
Paperback: 308 pages
50 great recipes for giving soul to your characters
by building high-quality rigs and understanding the
principles of movement
Learn how to create efficient and easy-to-use
character rigs
Understand and make your characters , so that
your audience believes they're alive
See common approaches when animating your
characters in real world situations
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Uploaded by [StormRG]
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