fxguide - visual effects news - Combustion: Using RLA or PRF files

I often get asked about using using RLA or PRF files created from Discreet's 3d max with Discreet's Combustion.....

Here is some RPF and RLA background and technical info that I hope you all find informative and useful!

regards,

Jack, denmark

RLA Files: The RLA format is a previously used with SGI computers and popular because RLA supports the ability to include arbitrary image channels. This means that, when you render and specify the RLA file for output, you can set RLA Image File parameters from a specific list. You specify what channels (and what format) you want to write out to the file.

The RLA Image File Format typically has a dialog box with the following options. Sidenote: the MORE info you include within that dialog, that larger the file size gets...

-Standard Channels: The standard channels are RGB color and the alpha (transparency) channel.

-Bits per Channel: Choose either 8 or 16 as the number of bits per channel. Default=8.

-Store Alpha Channel. Choose whether to save the alpha channel.
Default=selected.

When created from Discreets 3ds max, there are additional Optional Channels when you render your RLA files. There are eight additional channels that can be generated and also viewed in the virtual frame buffer:

-Z Depth: Displays Z-Buffer information in repeating gradients from white to black. The gradients indicate relative depth of the object in the scene.

-Material Effects: Displays the Effects Channel used by materials assigned to objects in the scene. The Effects Channel is a material property set in the Material Editor and used during Video Post compositing. Each Effects Channel ID is displayed using a different random color.

-Object: Displays the G-Buffer (p. v3-61 1) Object Channel ID assigned to objects using the Object Properties dialog. The G-Buffer ID is used during Video Post compositing. Each GBuffer ID is displayed using a different random color.

-UV Coordinates: Displays the range of UV mapping coordinates as a color gradient. This channel shows where mapping seams might occur. Note: UV Coordinates will not be displayed on objects that have the UVW Map Modifier applied unless a map has been applied that uses the coordinates.

-Normal: Displays the orientation of normal vectors as a grayscale gradient. Light gray surfaces have normals pointing towards the view. Dark gray surfaces have normals pointing away from the view.

-Non Clamped Color: Displays areas in the image where colors exceeded the valid color range and were corrected by 3ds max. The areas appear as bright saturated colors usually around specular highlights.

-Coverage: This saves the coverage of the surface fragment from which other G-buffer values (Z Depth, Normal, and so on) are obtained. Z-Coverage values range from 0 to 255. To see Z Coverage, render to an RLA file after first checking Z Coverage in the Setup sub-dialog, then choose Z-Coverage in the virtual frame buffer’s Viewing Channel dropdown list. The Z-Coverage feature is provided primarily for developers, and should aid
in the antialiasing of Z-buffers.

-Background: Saves the color of the object behind the front object. This channel is really only valid when the coverage of the front object is less than total, or when the front object is at least partially transparent. However, if a pixel on the front object completely covers a pixel on the back object, and is opaque, the background color channel is not generated for that pixel. Instead, it uses the color of the background. As with the Z-Coverage channel, this feature is primarily included for developers.

-Descriptive Information: This information is saved with the file, and includes: Description (You can enter descriptive text) and Author (You can enter your name)

Next, comes RPF:

RPF Files (Rich pixel Format): The RPF format is a 3ds max "Rich Pixel file Format" that builds on the older RLA format with additional arbitrary image channel information. While setting up a file for rendering an output, one simply selects these addiitional RPF Image File settings from the dialog setup list. You can specify what channels you want to write out to the file. Side Note: the more info you select and add to the list, the larger the files tend to be.

RPF files officially replace RLA files as the format of choice for rendering animations requiring further post-production or effects work. Many channels available in RPF files are exclusive to this format.

Important Tip: When you create a scene you plan to render as an RPF file for use with the Discreet combustion software, turn ON the Render Occlude Objects, located under the Object Properties Dialog, for objects in the scene. This is important if you want to use the combustion G-Buffer Extract feature. When Render Occluded Objects is enabled and you extract an object in combustion, the objects behind it are drawn correctly. If Render Occluded Objects is disabled (the default), objects behind the extracted object appear with black holes where they were occluded!

The RPF Image File Format has a dialog with the following options:

Standard channels Group: The standard channels are RGB color and the alpha (transparency) channel:

-Bits per Channel: Choose either 8 or 16 as the number of bits per channel. Default=8.

-Store Alpha Channel: Choose whether to save the alpha channel. Defaut=selected.

With 3d Max, there are additional Optional Channels for the output RPF files. These are additional channels that you can generate and also view in the virtual frame buffer:

-Z: Saves Z-Buffer information in repeating gradients from white to black. The gradients indicate relative depth of the object in the scene.

-Material Effects: Saves the Effects Channel used by materials assigned to objects in the scene. The Effects Channel is a material property set in the Material Editor and used during Video Post compositing. Each Effects Channel ID is displayed using a different random color.

-Object: Saves the G-Buffer Object Channel ID assigned to objects using the Object Properties dialog. The G-Buffer ID is used during Video Post compositing. Each G-Buffer ID is displayed using a different random color.

-UV Coordinates: Saves the range of UV mapping coordinates as a color gradient. This channel shows where mapping seams might occur. Note: UV Coordinates will not be displayed on objects that have the UVW Map Modifier applied unless a map has been applied that uses the coordinates.

-Normal: Saves the orientation of normal vectors as a grayscale gradient. Light gray surfaces have normals pointing towards the view. Dark gray surfaces have normals pointing away from the view.

-Non Clamped Color: Saves areas in the image where colors exceeded the valid color range and were corrected by 3ds max. The areas appear as bright saturated colors usually around specular highlights.

-Coverage: Saves the coverage of the surface fragment from which other G-buffer values (Z Depth, Normal, and so on) are obtained. Z-Coverage values range from 0 to 255. To see Z Coverage, render to an RLA file after first checking Z Coverage in the Setup subdialog, then choose Z-Coverage in the virtual frame buffer’s Viewing Channel dropdown list. The Z-Coverage feature is provided primarily for developers, and should aid in the antialiasing of Z-buffers.

-Node Render ID: Saves each object as a solid color according to its G-Buffer Object channel (found under Object Properties).

-Color: Saves the color returned by the material shader for the fragment. This channel displays any transparent fragment as a solid color.

-Transparency: Saves transparency returned by the material shader for the fragment. Any fragment with any degree of transparency will be rendered as a solid gray object.

-Velocity: Saves the velocity vector of the fragment relative to the screen in screen coordinates.

-Sub-Pixel weight: Saves the sub-pixel weight of a fragment. The channel contains the fractions of the total pixel color contributed by the fragment. The sum of all the fragments gives the final pixel color. The weight for a given fragment takes into account the coverage of the fragment and the transparency of any fragments that are in front of a given fragment.

-Sub-Pixel Mask: Saves the sub-pixel alpha mask. This channel provides a mask of 16 bits (4x4) per pixel, used in antialiased alpha compositing. This mask is especially useful with the combustion compositing product.

-Descriptive Information is information that is saved with the file, and includes Description (a descriptive text) and Author (You can enter your name.)

The above info is adapted and revised directly from the 3dmax version 4.0 User Reference Guide, volume three, pages 349 to 351.