Changing contrast of individual sprite

I'm trying to figure out how to change the contrast of an individual sprite, one that's part of a sprite sheet. I've seen shaders that allow the direct manipulation of texture contrast, but I can't quite wrap my head around how one would only apply it to an individual sprite and not the whole atlas. Obviously you can change the color tint/hue/saturation of individual sprites – would contrast be able to work the same way?

I'm just not sure where to start with this problem, if shaders can accomplish it, or if it's even possible. Any help would be greatly appreciated.