I can move the saturation slider all the way to the left to desaturate the entire layer, while leaving the layer above untouched.

You use one of the many selection tools that Photoshop has to offer and you select the iris of the eye.

The thing is, youre already happy with the way the iris is portrayed.

By doing this, youll have the ability to alter everything but what you initially selected.

This is a very handy bit of knowledge to have in your back pocket, so be sure to read the post all the way through.

Also, at the end, Ill give you a quick tip that will help accomplish the same task by using a different method.

I could go for one of the more advanced ones, but since I have yet to talk about them, I dont want to confuse anyone.

Because this is the case, Ill use the Elliptical Marquee Tool from the left toolbar.

Because the area Id like to select is round and challenging to accurate encapsulate, Im going to drag one guide from the ruler that runs along the top of my work area and another that runs along the left side.

For the top guide, Im going to rest the horizontal line right on top of the iris and for the left guide, Ill line it up with the leftmost edge of the iris.

Then, Ill rest my tool pointer right on top of the intersection of my guides and click and drag down and to the right.

When I feel the iris is selected to my liking, Ill let go of the mouse.

I know this sounds like a lot of steps.

It isnt. Just take a look at the photo below.

If you want to select something and make your selection either a perfect square or circle, simply hold down the Shift key on your keyboard as youre dragging the tool.

Also, if you dont see any rulers in your workspace, head up to the View Rulers menu and make sure that item is checked off.

To create a guide from a ruler, simply click on top of one of the actual rulers and drag your mouse outward towards where youd like the guide to rest.

When the mouse pointer changes to a different icon, you can click and drag anywhere youd like.

To do this, Ill head up to the Select Inverse menu item and click.

Instead of having the iris selected, the selected area reversed itself and now everything but the iris is selected.

To do this in a non-destructive manner, like I explained in this post and this post, Ill head over to the Adjustments panel and click on HueSaturation.

Now, the only reason Im giving this method is because this is a simple project.

So, if I click on the bottom layer with the photo in it and then head up to the Adjustments panel and click on HueSaturation again, I can follow the same exact instructions as I gave above.

Invert Adjustment Photoshop