The Posterize Effect makes a video look like a poster. Posterization reduces the number of colors available in your video. Pixels that are similar colors in the original are all converted the the same color, producing bigger areas of "flat" color and less shading..
Levels per Channel
Color information for each pixel is stored as three numbers, one each for red, green, and blue. These are combined to give the final color. Normally there are 256 possibilities for each. The Levels Per Channel reduces the possibilities for each channel. The lower the number of levels per channel, the larger the areas of flat color will be. This number can range from 2 to 20.