Section 11 Compositing - Avid DS Support Center

Section 11 Compositing - Avid DS Support Center

Section 11

Compositing

Duration: 60 minutes

This section describes the ways in which you can layer two or more images to create a new image. This is known as compositing.

The following topics provide information on compositing:

About Compositing

Compositing MethodsThe Layers View

Creating a Basic Matte

Simple Track Compositing

Using Composite Container Clips

Section 11 Compositing

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About Compositing

About Compositing

Compositing is the layering of clips or images to create a new integrated image called a composite. The underlying layers in a composite are only visible if your clip has a matte; a grayscale image that lets you isolate and protect specific parts of an image.

If an image already has a matte (called an internal matte), it is stored in its alpha channel. The alpha channel is one of the four components of an image: R

(red), G (green), B (blue), and A (alpha). If an image does not have a matte, you can create one or use a matte from another image (called an external matte).

In Avid DS Nitris, foreground images are composited over a background image using a matte from the foreground image’s alpha channel.

Foreground image

Matte in alpha channel of foreground image

+ =

Background image Foreground image composited over background

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Section 11 Compositing

Compositing Methods

In Avid DS Nitris, there are three methods that you can use to create a composite, depending on how complicated your composite will be. Before you begin compositing, you should know which clips you want to use and how you want to composite them.

In this section, you’ll learn how to create mattes, and perform composites using two different methods. n

In Avid DS Nitris Editor, compositing is limited to simple track compositing.

Method 1: Simple track compositing lets you use the video and background tracks to composite images. You can add as many video tracks to the timeline as needed.

Method 2: Composite container clips

let you create multiple layers and composites that can contain tracking, external mattes, or animation. You can also apply effects, such as color correction, DVEs, graphics, and keyers to each layer and blend composite operations between layers and mattes.

Clips on video tracks feed into layers in the Layers view.

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Method 3: Effects Trees are useful when you want to reuse the treatment of an element repeatedly within a composite. In an Effects Tree, you can apply any combination of image effects. This lets you combine multiple images on one layer, which serves as the input to the layer above it.

Note: Effects Trees are an advanced topic that is discussed in detail in the

Avid DS Nitris Compositing and Graphics

Guide—see “Using the Effects Tree to

Composite” in the Help.

Compositing Methods

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Section 11 Compositing

Creating a Basic Matte

A matte is a grayscale image that defines the transparency of an image when it is composited over another image. In Avid DS Nitris, there are several ways to create mattes.

Viewing the Alpha Channel

Before creating or adding mattes to a composite, you should determine whether the clip you are using has a matte. A quick way to check whether a clip has a matte in its alpha channel is by using the Viewer Alpha Full button above the Record Viewer.

The alpha channel is one of the four channels (or components) of information that is contained in each pixel of an image. This channel specifies the transparency of each pixel, allowing portions of the foreground image to reveal or block out the background image when two images are composited.

To view the alpha channel of a clip:

1. Open a new sequence.

2. Place the Rectangle clip at the beginning of a video track on the timeline.

3. Move the position indicator over the clip, select the clip and click the

Viewer Alpha Full button above the Record viewer.

The matte is displayed in the alpha channel of the clip. It is displayed as a grayscale image. By default the viewer displays the matte opacity at

100%. You can select the percentage of the matte opacity by right-clicking the Viewer Alpha Full button.

If a clip does not have a matte in its alpha channel, the entire channel would be white.

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Creating a Basic Matte

4. Click the Viewer Alpha Full button again.

5. Delete the Rectangle clip.

Keying out the Blue Background

Keying is an easy way to create a basic matte from a color in a foreground clip.

In the following example, you’ll be using the Blue-Green Keyer effect to create a matte based on a blue background color. You’ll learn how to create a matte for a musician who was filmed against a blue screen. For more information on keying, see “About Keying” in the Help.

To create a basic matte:

1. Right-click the overview area of the timeline and select Create

Background Track.

Overview area

A background track appears under the V1 video track.

2. Place the Musician clip at the beginning of the V1 video track.

3. Place the GiantWide-Bckg clip at the beginning of the B1 background track.

4. Select the Musician clip and view the alpha channel.

Notice that the clip has no matte. Therefore, you cannot successfully composite this clip over the background clip.

5. Click the Viewer Alpha button to see the musician in the viewer.

6. Apply the Blue-Green Keyer effect to the Musician clip.

The Blue-Green Keyer property editor displays.

7. Click the Pick Key Color button.

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Section 11 Compositing

The cursor changes to an eyedropper cursor when you move it over the viewer.

Eyedropper cursor

8. In the viewer, click the blue background color.

Now you can see the background image in the viewer. In the property editor, the color you chose is displayed in the color swatch beside the Pick

Key Color button.

9. In the property editor, select the Output Matte option to see the grayscale matte you created.

Transparent area is keyed out.

Opaque area is the foreground image that to be uses in the composite.

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Creating a Basic Matte

To make sure that the white foreground is completely white and the black background is transparent, you must clean the matte. The following procedure shows you how to do a simple clean-up. If you need to fine-tune the matte further, see “Fine-Tuning the Matte” in the Help.

To clean the matte:

1. Select the Matte property page and make sure that the Output Matte option is still selected.

2. In the Map box, adjust the Pick BG (background) slider until you get a solid black color in the viewer. This will make the background that you have keyed out completely transparent and ready for compositing over another clip.

3. Adjust the yellow Pick FG (foreground) slider until you get a solid white color. This removes all semitransparent areas, ensuring that the foreground image is completely opaque.

4. To view the result, deselect the Output Matte option.

n

Tip: If you make a mistake, press Ctrl + Z to undo. If you’re not satisfied with the matte, you can redo the entire procedure by clicking the Reset button.

To bypass the keyer and view the original clip, deselect the Output Matte and

Apply Key options on the Key property page.

5. Delete the clips on the timeline.

6. Delete the B1 background track.

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Simple Track Compositing

Simple track compositing on the timeline lets you use an unlimited number of video tracks in the Editing layout to create quick and simple composites.

As you add clips to the tracks, the result is displayed in the viewer. Remember, the overlaid clip must contain a matte in its alpha channel for the composite to display in the viewer.

If your clip does not have a matte, you can create one. You will learn how to do this later in this section.

Tracks are composited in the order in which they appear in the timeline. The topmost video track is the top layer in the composite.

On the timeline, you can add, remove, or reorder video tracks, as well as hide one or more tracks to see the impact of each video track independently—see

“Working with Tracks” on page 59 .

To create a composite on the timeline:

1. Place the Circle clip at the beginning of the video track. This will be the bottom-most layer of your composite.

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Simple Track Compositing

2. Right-click the overview area of the timeline and select Create Video Track.

Overview area

Timeline ribbon

A new video track appears on the timeline above all the other tracks.

3. Place the Rectangle clip at the beginning of the new video track.

4. Drag the Triangle clip to the beginning of the timeline ribbon.

A track containing the Triangle clip is automatically created at the top of the timeline.

The clip on this track is composited on top of the clips that fall within the same time span on the tracks below.

The result of composite corresponds to the video tracks and the order of the layers.

5. Place the position indicator over the clips to view the result in the viewer.

6. Save as Sequence4.

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Section 11 Compositing

Using Composite Container Clips

Working with layers in the Compositing layout lets you create complex composites that can contain tracking, external mattes, or animation. It is where you organize multiple layers of video clips and images. When compositing with layers, you are actually working within a composite container clip as soon as you switch to the Compositing layout. n

The Compositing layout is not available in the Avid DS Nitris Editor product.

Avid Explorer is where you can drag and drop clips: to the Layers view, the composite container clip timeline, or the Effects Tree.

Layers view is where you add clips and establish the order of the clips that are placed on the composite container clip timeline.

Navigation icons for moving between top timeline and container clips.

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Effects Tree is an alternate method of compositing and applying effects.

Container clip button

Using Composite Container Clips

A composite container clip lets you focus on the clips that you want to composite. When you create a composite container clip, you get a new timeline for layering clips on the video tracks of the Compositing layout.

When you close the composite container clip, the result is displayed as a single clip on the timeline in the Editing layout; this is the top timeline.

You can reopen a container clip at any time to add, modify, or delete its contents. You can also apply effects on individual clips, as well as the entire composite container clip.

Viewer displays the output of your sequence at the location of the position indicator.

Composite container timeline is where you place all the clips in your composite.

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Section 11 Compositing

To create a composite container clip:

1. Make sure the position indicator is placed over the clips on the timeline.

2. From the taskbar, click the Compositing button.

A composite container clip is automatically created and the Compositing layout is displayed. Two new buttons appear at the bottom of the taskbar; the top button lets you switch back to the top timeline in the Editing layout and the button beneath it represents the composite container clip that you are now working in.

Go to Top Timeline

Container clip

3. All three clips are now in your composite container clip.

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The content of the composite container is based on where the position indicator is on the timeline when you switched to the Compositing layout. If it is over a clip(s) on the timeline, this clip becomes the first layer. If the position indicator is over a transition, both clips become part of the composite.

To close a composite container clip:

t From the taskbar, click the Go to Top Timeline button at the lower end of the taskbar.

The current container clip is closed and the top timeline is displayed.

All composited clips are represented as a single container clip on the top timeline. To make any changes to the composite, reopen the composite container clip.

Composite container clip on the top timeline in the Editing layout.

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Using Composite Container Clips

To reopen a composite container clip, do one of the following:

t Double-click the container clip to open it.

t Place the position indicator over the container clip and click the

Compositing button on the taskbar.

The composite container clip opens and the Compositing layout displays the contents of the container clip.

The Layers View

The Layers view in the Compositing layout lets you apply animation, tracking, or external mattes to your layered clips. You can also change the order and appearance of the composited clips.

You can do the following for each layer:

• Apply the Color Correction, DVE, Graphics, and Keyer effects.

• Apply one or more external mattes to individual layers—see “Using

External Mattes in the Timeline and Layers View” in the Help.

• Apply compositing and blend operations between the RGB and alpha components of adjacent layers. This is an advanced topic that is not covered in this guide—see “Applying Blending Operations in the Layers

View” in the Help.

Layers view

Result area

Layers

Animation controls

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Section 11 Compositing

In this example, the layers were automatically created from the clips on the top timeline. You can, however, drag and drop other clips for your composite from the Avid Explorer to the timeline, or to the Layers view.

To create and view layers:

1. Drag the Clouds clip from the Avid Explorer to an empty area at the top of the Layers view.

A layer is created and a track is automatically created on the timeline. The clouds, however, are obscuring the shapes.

2. To rearrange the layers, drag the Clouds layer by the Layer button and place it at the bottom of the layers.

Layer button

Clouds appear behind the shapes.

For more information, see “Working with the Layers View” in the Help.

Applying Effects to Layers

When you apply an effect to a layer, it affects the duration of all material on its corresponding track on the timeline. You can bypass an effect to view the composite without the effect. For more information, see “Bypassing Effects” on page 102 .

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Using Composite Container Clips

You can apply four types of effects on each layer: Color Correction, DVE,

Graphics and Keyer. Applied from bottom to top, the effects on each layer work on the original image and are independent of each other.

Color correction

DVE

Graphics

Keyer

At processing time, the image is processed on the results of the preceding effect.

To apply an effect to a layer:

The final composite

1

Select the layer on which you want to apply an effect.

Note: When you select a layer, an Effects Tree displays in the area below the layers. Each layer have its own Effects Tree.

2

To apply an effect, select one of the options and click the button beside it.

The Key and DVE effects open a property editor.

The CC and Gfx effects switch to the Effects and

Graphics layouts respectively.

Tip: You can also open the floating Graphics combo view by pressing Ctrl and clicking the Gfx button.

3

Use any open property editor to edit and animate the effect. If you were switched to another layout, switch back to the Compositing layout by clicking the Compositing button on the taskbar.

4 Close any property editors that were displayed.

5 Save your sequence.

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When you apply an effect to any of these layers, and Effects tree will display in the view below the Layers view. Each layer will have it’s own Effects tree.

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Section 11 Compositing

Viewing the Results of Composited Layers

The viewer displays the resulting composite of all the layers. You can view each layer independently of the other layers by soloing or muting layers.

When you solo a layer, only that layer is displayed in the viewer. Soloing a layer has no effect on the processed result, which is useful when you want to view one layer without seeing the effects from other layers. You can only solo one layer at a time.

If there are several layers in your composite and you want to preview two or more layers and not the others, you can mute them. When these layers are muted, they are not displayed in the viewer. Muted layers are not included in the processed result either.

To mute or solo a layer in the Layers view:

t Click the Mute or Solo button on a layer.

Mute button

Solo button

Depending on your viewer’s settings, the corresponding layer’s RGB or alpha channels are displayed in the viewer.

To solo a layer on the timeline:

t Click the Solo button on a video track on the timeline.

Using the Result Area

The result area at the top of the Layers view displays the final composite of all your layers. There is a thumbnail for the RGB and alpha channels, so you can see the resulting image and matte separately.

RGB thumbnail

Result Alpha thumbnail

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Using Composite Container Clips

You can hide the result area if you need more working space. As an option, you can view the output of the result area in a separate floating viewer. This lets you view the output of your effect.

To use the result area:

t Right-click the result area and select one of the following:

-

Display Result Area to show or hide the result area.

-

Open Viewer to view the output of the result area in a separate, floating viewer that you can reposition anywhere on the desktop.

Close the viewer when you’re done.

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