a cell shader reponds to light Much like anything else but instead of shading a image or object by varying the brightness per pixel it Usually breaks the light into zones and colors. So for example if you where to take a picture of your face and put a light on it, it would break your face appart into 2 to 5 color tones but in reference to the light, Almost like Posterizing an image but only based the the light intensity, dirrection and a color range.

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