Lightscape User Guide

14 Rendering

Creating Images

Lightscape produces images that can be output in a variety of standard file formats. The following file formats are currently supported:

File Extension: Format:

.bmp

.tga

.tif

.rgb

.jpg

.png

.eps

Windows native file format.

Targa, TrueVision format.

TIFF—24-bit and 48-bit.

RGB—24-bit and 48-bit, native

Silicon Graphics file format.

JPEG.

Portable Net Graphics.

Encapsulated PostScript.

Rendering with OpenGL

You can produce an image of your radiosity solution very quickly using OpenGL rendering. However, keep in mind that rendering occurs at—and can be limited by—the color depth of your display device.

This color depth may be less than 24 bits per pixel, reducing the quality of your output.

Note: You can avoid hardware limitations by ray tracing with the lsray utility. This batch processing utility runs in software only and, therefore, does not depend on your display hardware. It can always output images with 24-bit color per pixel (or 48-bit color per pixel in the TIFF and RGB file formats). For more information on the batch processing utilities,

see “Rendering Large Jobs” on page 220.

Image Resolution

You can choose from a variety of commonly used image resolutions provided by Lightscape, or you can specify a custom resolution. When you set the resolution, the Graphic window resizes itself accordingly.

Note: When you resize the window, the aspect ratio (proportion) may change and the view may be altered. Resize the Graphic window before setting your views so that you can see exactly what will be rendered.

To take advantage of accelerated OpenGL display capabilities, the image must fit within the bounds of the Graphic window. Images that have a higher resolution than the window’s dimensions are broken into tiles. Each tile is the maximum size that fits within the window while maintaining the original aspect ratio of the image.

For example, if you create an 1800 x 1200 image

(larger than the maximum Graphic window size),

Lightscape breaks up the image and renders it as four tiles of 900 x 600 pixels each. Once it has generated the image for every tile, Lightscape creates the final high-resolution image by combining these tiles.

Antialiasing

Use antialiasing to smooth out jagged edges. This improves image quality and provides better results when the model contains features smaller than a single pixel.

Although a single still image requires antialiasing to achieve high quality, the antialiasing level can be lower than that required for animation frames. It is much easier to see aliasing in animations, particularly if the model contains many thin (less than a pixel) features, such as cables or railings. You can obtain satisfactory single images with an antialiasing level set to 3 or 4; however, animation frames may require a level of 6 or 7.

To render a radiosity solution:

1.

Choose File | Render.

The Rendering dialog appears.

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Creating Images

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Antialiasing Algorithms in Lightscape

Lightscape uses different antialiasing algorithms depending on whether or not ray tracing is used. If ray tracing is not used, OpenGL image generation uses either a software or (if available) a hardware accumulation buffer. It jitters the original images a number of times by a slight subpixel amount and then averages these images to produce a single high-quality image.

This process requires the image to be displayed n times, where n is the square of the antialiasing level selected. For example, an antialiasing level of 2 displays the image four times to create the final image.

A level of 10 displays the image 100 times (taking 100 times longer to create than the non-antialiased image).The ray tracer uses a different adaptive scheme that is more efficient for this process. So, with the ray tracer there is no direct correlation (as with the OpenGL method) between the antialiasing level and the time required.

2.

To enter a path and filename, do one of the following:

• Enter a path and filename for the rendered image in the Output File Name box

• Click Browse and navigate to the location in the

Open dialog, enter a filename, and click Open.

• Select the output format and pixel depth required.

3.

list.

Select an image resolution from the Resolution

4.

To define a custom resolution, select User Defined from the Resolution list and enter the dimensions for the image in the Width and Height boxes.

5.

To increase the number of antialiasing samples, select the appropriate level from the Antialiasing

Samples list.

Antialiasing Samples list

Note: Increasing the antialiasing level will increase your rendering time.

6.

Click OK.

Rendering with Ray Tracing

With Lightscape, you can create high-quality ray traced images that render effects such as specular reflections and refraction through transparent materials.

In addition to the Image Resolution and Antialiasing

options described in “Rendering with OpenGL” on page 214, the following options are available when

you use ray tracing.

Ray Trace Direct Illumination

This option ray traces direct light contributions from lighting sources (the sun and luminaires marked for ray tracing). Use this option to correct shadow aliasing problems and provide additional enhanced lighting effects, such as highlights on nondiffuse surfaces. For more information, see

Chapter 11, “Radiosity Processing,” and Appendix

D, “Reflection Models.”

Remember that the time required to generate images can increase significantly with the number of light sources that are ray traced.

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14 Rendering

Soft Shadows From Sun

By default, Lightscape renders shadow boundaries caused by the sun as sharp edges. Enable this option to blur the edges to provide a more realistic and natural shadow boundary.

Note: This option can significantly increase the rendering time of an image.

Shadows From Inactive Layers

Use this option to cause objects on layers that are not on (not visible) to cast shadows. The objects will not appear in the image, but their shadows will appear.

OpenGL Compatible

Because OpenGL and the Lightscape ray tracer use different reflection models, images created from the same Solution model do not look the same rendered with OpenGL as when rendered with the ray tracer.

The OpenGL Compatible option forces the ray tracer to generate images that closely match the

OpenGL display rendering. It also adds specular reflections, but does not render them to as high a quality as is possible when this option is not enabled.

For more information, see Appendix D, “Reflection

Models.”

Ray Bounces

To control how many levels of reflection or transmission are calculated during ray tracing, specify the number of ray bounces tracked in this box.

For example, if you want to see through two windows, set this option to at least 2. Keep in mind that if you actually model the panes of glass with two surfaces each, you must set the number to 4.

If regions of the image that contain transparent objects look incorrect, increase the number of ray bounces.

Note: If the number of bounces is set to 0, you will see no specular or transparency effects. The default value for this parameter is 10.

Top: Two facing mirrors with Ray Bounces set to 1

Bottom: Two facing mirrors with Ray Bounces set to 10

To ray trace an image:

1.

Choose File | Render.

The Rendering dialog appears.

2.

To enter a path and filename, do one of the following:

• Enter a path and filename for the rendered image in the Output File Name box

• Click Browse and navigate to the location in the

Open dialog, enter a filename, and click Open.

• Select the output format and pixel depth required.

3.

list.

Select an image resolution from the Resolution

4.

To define a custom resolution, select User Defined from the Resolution list and enter the dimensions for the image in the Width and Height boxes.

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