The video filter performs the second pass of the analogizing algorithm. The first pass is done in the blender and involves anti aliasing of internal edge or non-silhouette edges. After the image is rendering into the framebuffer, all pixels except those that are on the silhouettes of objects will be fully covered (coverage value = 1.0). For partially covered pixels, the video filter performs a linear interpolation between the foreground color and the background color:
OutputColor = cvg * ForeGround + (1.0 - cvg) * BackGround
The ForeGround color is always the color stored in the frame buffer for that pixel. The BackGround color is found by examining fully covered pixels in a 5x3 pixel area around the current pixel. Note that Z is not used in determining the BackGround color and so it is safe for Z to be single-buffered.