Autodesk 12812-051462-9011 User Guide 3 - Page 2842

to reflect this. For example, a pixel that is 30% covered by the object will have an alpha of 0.30. To antialias the edges, the alpha must be premultiplied to darken these edge pixels. (This is equivalent to compositing the image over a black image). So it is natural, in a sense, for rendered images to have premultiplied alpha. If you do not premultiply the alpha of a rendered image, then just looking at the RGB you will see jaggies on the edges of objects. You would need to composite it against black using the alpha channel whenever you wanted to display it. NOTE To control whether or not the renderer uses the environment map's alpha channel in creating the alpha for the rendered image, choose Customize > Preferences > Rendering, and then turn on Use Environment Alpha in the Background Antialiasing group. If Use Environment Alpha is turned off (the default), the background receives an alpha value of 0 (completely transparent). If Use Environment Alpha is turned on, the alpha of the resulting image is a combination of the scene and background image's alpha channel. Also, when you render to TGA files on page 7370 with Pre-Multiplied Alpha set to off, turning on Use Environment Alpha prevents incorrect results. TIP If you plan to composite objects in another program such as Combustion or Photoshop, render the objects against a black background. Otherwise, a fringe of environment or background color can appear around the objects. Procedural Maps Unlike a bitmap, which is an image produced by a fixed matrix of colored pixels like a mosaic, a procedural map is generated by a mathematical algorithm. Consequently, the types of controls you might find for a procedural map will vary depending on the capabilities of the procedure. Glossary | 8097