I'm wondering why the greyscale and saturation filters were both necessary. greyscale(0) == saturation(1.0) and greyscale(1.0) == saturation(0.0), with afaik a

I'm wondering why the greyscale and saturation filters were both necessary. greyscale(0) == saturation(1.0) and greyscale(1.0) == saturation(0.0), with afaik a linear scaling between either.