How to create a saturation gradient

Say I want to create a gradient that only affects saturation, how do I do that? Example: I have an image that I want to hint at perspective in. I want the objects farther back in space (top) to be less saturated and those closer to the foreground (bottom) to be more saturated. I'm assuming I can do this with an adjustment layer and I've tried messing around with it, but it seems that I have to set colors to create a gradient but I don't want to affect the native colors at all, I just want to change their saturation. I'm not talking about going from B&W to color. I want to be able to set a particular level of desaturation grading to another level of saturation up to 100%.

You'll use a black-to-white gradient _mask_ for your adjustment layer. Experiment with where you start & end the gradient until you're satisfied. Of course, set saturation to a minus value.

Allison:

Create a hue/saturation adjustment layer. You'll see a mask associated with the layer (thumbnail to the right of the adjustment layer icon in the layers panel). Use the gradient tool on that layer mask.

J

Thanks, I figured it out. I created an adjustment layer, added a black to transparent gradient, set it to saturation and simply lowered the opacity to taste.