Can you give a small (runnable) code snippet illustrating your problem?

I don't think that the tint() method will do what you want. You can use HSB values as arguments to tint() but that is just another way of specifying the tint colour. If I understand your post correctly, then what you want to do is alter the saturation of each pixel in the image. I could be wrong, but I don't think that processing has a built-in filter for this; you will probably have to manipulate the pixel array directly.