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Photoshop CS4's adjustment features offer unparalleled opportunities to correct and manipulate images. In Photoshop CS4: Image Adjustments in Depth, Jan Kabili explains how to use all the major Photoshop adjustment features. She shares the best techniques for adjusting image quality, and shows how to use the new Adjustments panel to streamline a photo correction workflow. Jan also demonstrates multiple ways to eliminate color casts, and explains how to use the new On-Image Curves control to adjust brightness and color. This course offers a detailed look at the techniques photographers and designers use to master image adjustments in Photoshop. Exercise files accompany the course.
There is another way to use Levels to remove a color cast from an image, and that's to go into the individual color channels in a Levels adjustment, and tweak the mid-tone slider there, and that's what I'm going to show you how to do in this movie. As I showed you how to do in an earlier movie about Color Samplers and the Info panel, I've already added some color samplers to this image to help me identify the color cast and remove it. There are three Color Samplers here, one here in the highlights, one here in the shadows, and the one I'm going to use in this technique is right here, it's hard to see, it's color sampler number three, and it's one this gray rock, right here. And the reason that I put it there is that I would like that particular gray to be a neutral gray, after I have made my color correction. And that will help all of the other tones fall into line, and remove the color cast that's in this image.
It's hard to know from just looking at the image exactly what that color cast is because I took this picture in the Caribbean, and the water was a strange color to me anyway. So I'm not sure exactly what color everything should be, but I know that it doesn't look exactly right. To figure out what the color cast is, I'm going to go to the Info panel and to read out here for that Color Sampler number three. This is the current RGB value for the pixels under Color Sampler number three, and as you can see there is almost an equal amount of green and blue, but there is much less red at that point. What I'm trying to do is get all three numbers the same here and that will mean that gray rock really is a neutral gray. Well, if you think about it, green and blue makes cyan, and so what I've got here in this image is a cyan color cast, and now that I have a look at the image. That makes sense.
So I want to reduce that cyan color cast, and you maybe remember from the Color Wheel that I showed you earlier that the opposite of cyan on the Color Wheel is red. So if I add some red, I should be able to get these three numbers just about the same, and neutralize the mid-tones in the image. So that's how I'm going to remove the color cast, and I'm going to use Levels to do it. I'll go to the Adjustments panel, and I'll click the Levels icon to add a Levels adjustment layer. This menu is telling me that I'm currently working in the RGB Composite Color Channel, but I can get in and access the individual red, green and blue channels by going to this menu and choosing one of those individual channels from the drop down, or I could use a shortcut for the channels here, and I want to mention something for those who have been using Photoshop for a while, and are used to the channel shortcuts.
They changed in this version of Photoshop. So now the shortcuts for the red, greed and blue channels respectively are Option+3, Option+4, and Option+5 on the Mac, or Alt+3, Alt+4 and Alt+5 on the PC. So you'll have to learn those new shortcuts, if you are someone who likes to use shortcuts. For the rest of us, we'll use this drop down menu to access the individual color channels. I know that what I want to do here is increase the amount of red in the mid-tones. So I'm going to select the red color channel. Now I'm looking here at the histogram for just the red channel, and under that histogram, I have my input level sliders, which I have taught you about in the earlier movie on correcting tone and contrast with Levels.
The slider I'm interested in now to correct the color cast is just the gray slider here, the mid-tone slider, because I'm in the red channel if I click on this mid-tone gray slider and I move to the left, I'll be increasing the amount of red in the mid-tones, and I'm going to stop for just a minute, because I want to come up here and tell you to keep your eye on this number right here, which is the amount of red in the mid-tones. What I'm trying to do is get that number equal to the amount of green in the image, and I'm using green as my reference point, because of these three values that's the middle value.
So I'll go back down to that gray slider, and I'll keep moving to the left until I have got that value at 153. Now if you don't get exactly to 153, that's fine. You just want to be close. To see what that's done to the image, I'm going to go down to the Previous State icon here at the bottom of the Adjustment panel, and click and hold, and keep your eye on the image as I do that. This is how it was when I started, and this is how it is now, and I've removed a lot of that color cast already, but I see that there's a still a little bit more blue in the mid- tones, than there is green and red.
So I'm going to switch to the blue channel here, and I'm going to take the gray slider in the blue channel and drag to the right trying to get that value to 153 also, and I did manage to do that, but again, you don't have to get it exactly to 153, but what I have managed to do now is to neutralize that gray that's under color sampler number three. And the other tones have also fallen into place around that changed mid-tone, so that you can see when you look at the image that it's no longer cyan. And if I come down to the bottom of the Adjustments panel, and I click on the Previous State icon again, you can see the image as it started and the image as it is now.
So that's how to use the individual color channels and Levels to remove a color cast. In the next movie I'm going to show you how you can use Curves to remove the color cast.
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