Pacific Northwest Nature Photographers Tips, Tricks, Techniques & Tutorials
Removing Color Casts in Photoshop CS
by Mark Hudon
The intent of this article is to help the reader gain essential proficiencies in photoshop to improve the presentation of a digital photograph. Special thanks and credit to Barry Haynes for his excellent book, Adobe Photoshop CS Artistry, from which this information is derived.
Basic Solving for White (or Black)
First of all, go to the Levels dialog box and double click on the white eyedropper. Change all the RGB values to 244 and click okay. This is so that when you print the photo you’ll actually have some ink on the paper rather than bare paper, which looks bad.
Click on the black eyedropper and change all the RGB values to 8. This will actually give you a wider range of blacks that will print otherwise you'll end up with a lot of blocked up black in your prints.
When you leave the Levels dialogs another dialog will come up asking you if you want to save these changes, click yes.
Open your photo and open up a Threshold Layer. Your photo will become pure white and pure black. Slide the toggle to the left so that you see the smallest point that is black. Hold down your Shift key and click on that spot. It can’t be a tiny, tiny spot, one pixel, it has to be about the size of the lead in a pencil.
Now move the toggle to the right to find the first white spot. Hold down the Shift key and click on that spot. You’ll be leaving a marker at that spot so you can find it later.
Dismiss the Threshold layer by clicking Cancel. Your markers may disappear but don’t worry.
Call up a Levels layer.
Single click on the White Eyedropper and click on your white point. Voila! What you wanted to be white is now white not gray.
Single click on the Black eyedropper and click on your black marker. Voila again! the blacks are black and your photo should look much better.
This method will get you really close to the correct colors in most situations. Sometimes, if there is no real white, like a sunset or a dark forest scene, using the white eyedropper on the lightest spot will make your colors all weird. Sometimes the black eyedropper alone will be enough to get you where you want to be. There are other methods and a continuation of this method to exactly get rid of any color cast. That’ll be another tutorial though.
Advanced Solving for White and Black
There are a few things you first need to set up and to learn to make your Photoshop experience easy and efficient.
1) If you hit the F key, the scroll bars will disappear, your photo will center itself and your whole screen will turn gray. This is a good thing. You’ll now be able to grab your photo via the Hand tool and move the photo anywhere you want. This is much easier and faster than using the scroll bars.
2) If you press the spacebar and hold your mouse button down the cursor will turn into the little hand and you can grab the photo and move it anywhere you want. Anytime, any tool, press the space bar, click and hold the mouse button and you’ll get the Hand Tool. Very convenient.
3) Press the spacebar and the Command (Control, PC) to get the Magnifying Tool. Anytime, any tool, press the space bar and the Command key and you get the Magnifying tool. Very convenient.
4) I have a nineteen inch monitor at home. It’s nice but it’s a tiny bit cramped when I have my pallets and a photo displayed on it. For a vertical photo I have my pallets set on the left side of the screen, for a horizontal photo they are on the bottom. If you go to Window>Workspace you can save and name your “workspace”. Move the pallets to where you want them, go to Window>Workspace>Save Workspace. I named mine simply vertical and horizontal.
5) The pallets I have showing are the Layers pallet, the Action/History pallet and the Navigator/Info pallet.
Okay now for the fun part.
You should have at least the Levels and the Navigator/Info pallet showing.
Open a photo and run through the first Solving for Black tutorial up to where you have clicked on the two makers with the white and black eye droppers in the Levels pallet.
Look at the Info pallet and you’ll see a #1 and #2 with a list of R G B and numbers to the right. You’ve clicked on the lightest and darkest areas of your photo and your light area should read 244, 244, 244 and the darkest 8, 8, 8.
They probably don’t show those numbers though. Let’s say they show, for the dark point, 10, 12, 25. The numbers are showing you the value of the R, G and B channels. These numbers are showing you that you have a Blue cast to your darkest point and that you are not showing a true black.
Click in the Channel popup and move to the first color channel, the Red channel.
You’ll see a row of boxes with three numbers above the Histogram. The left one is for Darks and the right one is for the Lights. Click on the left one and, using the up and down arrows on your keyboard, increment the number up or down till the number for the Red in the Info pallet is 6 or 8. Move to the next color via the pop up and do the same thing. Try to get the numbers all the same.
Now do the Lights, making all the numbers 244. At the very least, make all the number the same close to 8 and 244.
This method works most of the time, in fact, for me, almost all of the time. It’s an objective method for removing any color cast from your photo. It doesn’t depend on your eyes, your opinion or your monitor.
Mark