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Color correction is the act of adjusting the color temperature of your images, either to compensate for a colorcast or over predominance of a color or subjectively to give your images a certain feel. Color temperature is measured in degrees Kelvin with a temperature of 5500 K being considered the temperature of overhead light of midday. Adding more yellow to your images will give them a higher color temperature and make them warmer. Adding more blue to your images will give them a lower color temperature and make them cooler. To start with, I just want to point out that having an over predominance of color is not necessarily a bad thing.
This image has an obvious colorcast. It's shot late afternoon, it's bound to be yellow. That's the whole point of the image. On the other hand, here I have a cool image that was shot somewhere around midday and the color temperature is a lot lower as a consequence, not necessarily a bad thing, although looking at it, I think it does look a little bit on the blue side. But, my point being that a colorcast is not always a bad thing. We're going to look at just fixing up this image and there are essentially two approaches we can take, and they are very much related to each other.
Most of what we need to know about Color Correction is constrained in this diagram. We see red, green and blue, additive primaries, and as cyan, magenta and yellow as subtractive primaries. Opposite to red is cyan, opposite green is magenta, opposite blue is yellow. So, if we have an image that has an over-predominance of yellow, if we are in a CMYK image that has a yellow channel, we can just reduce the amount of that yellow. But if we are in an RGB image, there is no yellow channel.
So what we can do is we can work on the blue channel, and by increasing the blue, we will be reducing the yellow. Likewise, if we have an image that has an over-predominance of red, let's say it's an RGB image, well, we can just reduce the amount of red by working on the red channel. But if we are in a CMYK image, maybe there is no red channel. Not maybe, there is no red channel. So instead, we can work on the cyan channel. By increasing the amount of cyan, we reduce the amount of red and the same is true with magenta and green; they are the complements of each other.
So increasing the magenta decreases the green and vice versa. Just keep this diagram handy and you can always figure out what you need to do to an image to adjust any sort of colorcast that it might have. Another approach is to target neutral midtones and that's where we'll start and we've already had a look at this working in the previous chapter, this involves using the great point eyedropper. What I am going to do first of all is if I go to my Eyedropper tool, I see that I've already put a sample point on this patterned carpet in the foreground and I have sampled that particular point, because as you can see, it is a gray segment of that carpet.
And my subjected decision here is that if this image had not had a colorcast and it has a colorcast because it's been shot indoors, so it has a yellowish feel to it. But if it didn't have that then that gray would be neutral. Neutral gray means RGB values the same or close to be the same. So that's what we are going to aim for and we are going to use this as our reference, as our target point. So I am gong to come to my Curves adjustment, I could do in Levels or Curves and then I am going to choose my gray point dropper and I am going to move over and I am going to click on that target point.
Now before I do so, I want to open my Info panel so I can see what the color values at that point are. And we see that I have Red a lot higher than green and then we have blue which is trailing some where behind. So by targeting that point as my neutral midtone, what it's going to do is it's going to set those colors all to be the same. And we can see what's happened with the curve. The red has been reduced, the blue has been increased and the green stays more or less the same ever so slightly increased.
The result at that point right there, we've got neutral values. That has an effect that goes throughout the image; it ripples up to the highlights and down to the shadows. Does it make it a better image? I don't know, I don't think so. I kind of like the warm feel that it had to it before. So, let's say that this is a step in the right direction, but we just want to moderate the whole effect and what we could do is reduce the Opacity somewhat and we have introduced some of the original yellow feel, the warmth of the original image back in, but the overall result is now, here was the starting point and here is the finishing point.
So we've targeted an area that's subjectively and I can't stress enough how much subjectivity is involved in this and we've said make that neutral gray and that affects the rest of the image. Now there is another approach we could take care. I am going to turn off that curve and this is basically suggested by this diagram that we looked at earlier. If we can say that this image has too much yellow in it, if we are in agreement that it has too much yellow, then to reduce the yellow what we can do is increase the blue.
And we can do this with a number of Photoshop's tools, one of which is the Color Balance adjustment layer. So I am going to choose Color Balance and now if I move towards blue, I am moving away from yellow and we also saw that we need to reduce the red. So if I move towards cyan, I am moving away from red. And that's going to give us a result very similar to the result we saw before. This is the result with Color Balance and now I've turned that off, we are back to the original, and this is the result with the curves.
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