An Easy Way To Find Neutral Gray - Part 2

Step 3: Change The New Layer's Blend Mode To 'Difference'

Next, back in the Layers palette, change the blend mode of the new layer from Normal to Difference.

The "Difference" blend mode isn't one that's used too often since it tends to make images look, shall we say "weird" and, well, some may even say "frightening", as we see here with how my image currently looks after changing the blend mode to Difference:

Believe it or not though, there is a method to the madness. The way the Difference blend mode works is that it compares the layer with the layer(s) below it and looks for differences between them (hense the name). Any areas in the layer which are different from the layer(s) below it show up as strange colors in the image, which is where the purples, blues and yellows are coming from in the image above, but any areas which are identical between the layers show up as black, or at least almost black if they're not 100% identical but still pretty darn close to it. In other words, with the Difference blend mode, any areas between the layers which are identical become the darkest parts of the image, and we can now use that to locate any areas that are supposed to be neutral gray.

How? Simple! We're now comparing our image on the Background layer with the layer above it that's filled with 50% neutral gray, which means that any areas in our image which are closest to that midtone gray color will now appear as the darkest parts of our image, thanks to the Difference blend mode. So now, finding a midtone gray area is as easy as finding the darkest part of the image!

Step 4: Add A 'Theshold' Adjustment Layer Above The 50% Gray Layer

With the 50% Gray layer still selected in the Layers palette, click on the Create New Fill Or Adjustment Layer icon at the bottom of the Layers palette and add a Theshold adjustment layer. Then, when the dialog box appears, click on the little white triangle at the bottom and drag it all the way to the left, which will turn your image temporarily white.

Now slowly begin to drag the triangle to the right until you begin to see black areas appearing in your image. The first black areas that appear are the neutral gray areas you're looking for. This is the exact same way you would normally find the darkest parts of the image when you're removing any color casts from the shadow areas, but now, thanks to the Difference blend mode, these darkest areas represent the areas closest to midtone gray. Click OK once you have a black area on the screen just large enough that you can select it with the Color Sampler tool, since that's what we'll be doing next.

Step 5: Select A Black Area With The Color Sampler Tool

Grab the Color Sampler tool from Photoshop's Toolbar (it's grouped in with the Eye Dropper tool), or use the handy keyboard shortcut Shift+I until you get to it, and click on an area of black in the image to add a marker. Zoom in on the area first if it makes it easier to select your black area, as I've done here:

We now have the darkest area of the image selected, which is our neutral gray area.