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The most flexible way to remove a color cast in Photoshop is to use Curves. In the past, Curves got the reputation for being relatively complicated to use, but I promise you that it's got much easier and more intuitive in Photoshop CS4, if you use a Curves adjustment layer as opposed to a direct adjustment, and that's because you could use the new On-image control in a Curves adjustment layer to remove a color cast. In an earlier movie I showed you how to use that control to adjust the contrast and exposure in an image. In this movie, I'll concentrate on removing color cast with this control.
I'll start by adding a Curves adjustment layer by going to the Adjustments panel and coming down to this icon, the Curves icon and clicking. There's the new Curves adjustment layer in the Layers panel, and in the Adjustments panel you can see the Curves graph and some controls for Curves. Right away, I'm going to enable the On-image feature, because with that on, my color correction workflow will be different than it would be, if that feature were not enabled. So I'll come up and I'll click on the On-image icon right here, and then I'm going to move my cursor into the image, and what I'm going to do is to look for an area that I think should be neutral.
To see whether it really is neutral, or whether there is a color cast, and if so, what that color cast is. There is some gray in the horse's skin, and I think that should be neutral gray. So I'll move my mouse over the gray area of the dappled skin and then I'll take a look at the Info panel, which is opened at the top of the screen. If your Info panel isn't open, you can open it from the Window menu. In the top left corner of the Info panel, I see the RGB readout telling me, the red, green and blue values for the pixels under my cursor. As you can see the green value is higher than the red and blue values, it's 196 as oppose to a blue value of only 173, and a red value in between of 188. If the grays under my cursor were indeed neutral, than these three numbers would be the same, and so my goal is going to be to get those three numbers the same, as I remove the color cast.
As I mentioned in an earlier movie there are two numbers for each color value there, because the numbers on the left side of the slash represent the current RGB values, and after I do the correction, the numbers on the right side of the slash will show the corrected RGB values. The first thing I want to do is to set a color sampler here so I can preserve the RGB readout in the Info panel. Because I have the On-image controls on, they make my cursor act just like a color sampler tool. So I don't have to bother going and getting the color sampler tool; all I have to do to add a color sampler is hold down the Shift key and click. And there is my color sampler 1, and you can see in the Info panel that now down here is the readout for that color sampler, which reveals the RGB values of the pixels under the color sampler.
The way I'm going to get rid of this color cast is to use the individual red, green, and/or blue channels in the Curves adjustment. I might have to use more than one panel. So I want to put a point on the curve on each of those channels. The way to do that is to come in to the image again, to move over that color sampler and to hold down the following shortcut keys. I'm going to hold down the Command key and the Shift key on a Mac, that's Ctrl+Shift on a PC, and click right in the middle of that color sampler.
Now I'm going to go into the Curves Adjustments panel where I can see that I'm currently looking at the curve for the RGB composite channel. I want to access the individual color channels, in particular the Green Channel, because what I want to do is reduce the amount of green in the sampled pixels. So I'll go to this menu in the Curves Adjustments panel, click, and I can choose the Green Channel from here, or I could use the shortcut Option+4 or Alt+4. By the way, if you are used to using shortcuts to access individual color channels for Curves, note that they have changed in Photoshop CS4.
Now for the red, green and blue channels respectively, the shortcuts are Option+3, Option+4 and Option+5 on a Mac or Alt+3, Alt+4 and Alt+5 on a PC. So to access the Green Channel, I can either choose Option or Alt+4, or I can choose Green from this menu. Now I'm looking at the curve for just the Green Channel, and you can see that on that curve, there is the point that I just added to all three of the channels. I can see that that point is selected, because it's solid, and the other points on this line are not solid; meaning that this is the selected point. But if it wasn't selected, I could cycle through to select the individual points by clicking either the plus or minus keys on the keyboard.
But since that point is already selected, all I'm going to do now is move it down in order to reduce the amount of green in the mid-tones. I could click on that point and drag, but it's a lot easier to make changes in Curves by using the arrow keys on the keyboard. So I'm just going to press my Down arrow, and as I do, I'm going to keep my eye up here on the green value, and I'll watch it get lower, and I'm going to try to make it equal the red value which is the middle of the three values. I went a little bit too far, so now I'll press the Up arrow and I'll just leave it at that. 189 is close enough.
Next I want to get the blue value in sync with the other two values. So I need to increase blue, and do that I'm going to go to another channel, the Blue Channel. So I'll come down to my Channel menu in the Curves Adjustments panel and I'll choose the Blue Channel. There's also a point on the curve for the sampled pixels in this Blue Channel, and that point is selected. It's a solid point. So all I need to do to increase the amount of blue is click the Up arrow key on my keyboard. By the way, if I hold the Shift key down, as I do that, I can move in larger increments, but I'm actually pretty close here, so I'm just going to keep clicking one click at a time, until I'm close to the values of the red and the green channels. And if I use the Down arrow once, I'll move down to 188. So I think that's about as closer as I'm going to be able to get, and what I've done is to neutralize the color of the gray under the color sampler right here.
And by doing that I've remapped all of the other tones in the image, removing the color cast from the mid-tones. If I want to see the difference between how the image is now after the correction, and how it was when I started, I'll come down to the bottom of the Adjustments panel and click the Last State icon right here. So this is how it was, and you can see now that there was a green cast, and this is how it is now with the neutralized mid-tones. I am going to go back to the RGB composite channel by choosing it from this menu. This is where I'm going to stop on this particular image, but if I was working with an image that looked like it also had a color cast in the highlights or the shadows, I would go through the same procedure setting color points in those areas, and using the individual channels in the Curves Adjustments panel to remove the color cast from those areas.
So as you can see the workflow in Curves using the On-image adjustment is really pretty intuitive and accessible. Curves really is the most complete place to go to do color correction and tonal correction. So I urge you to take the time to get to know and use Curves, so that you have the most control possible over color and tone in your own images.
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