In this exercise we are going to take a look at ways to adjust the composite histogram here inside of the Adjustments palette, and in subsequent exercises we will take a look at Output Levels, we will take a look at adjusting the histogram on a channel by channel basis, and a few other nuanced modifications that you might apply. So I'm still working inside of the photograph of Max, but I have gone ahead and saved my progress so far as an image called Semi-corrected.psd and notice that I have gone ahead and named this adjustment layer that I have created. I have called it Auto Color, Clip 0.2%, which is for the shadows, and 1.5%, which is for the highlights.
You would normally be able to confirm that by going up to the Adjustments palette here. You just click on this adjustment layer, go to the Adjustments palette, theoretically it would be open for you, and you would just Alt+click or Option+click on Auto, and that would bring up your last hue settings. Now it's working for me because I just got done applying them. For you however, when you open up this image, assuming that you are using the first version of Photoshop CS4 and they haven't bugged fixed this yet, it's probably going to reset everything to Enhance Per Channel Contrast and the Clip values will be their defaults of 0.1% apiece.
So it doesn't remember the previous settings, which is really actually not a good thing, but anyway you could reset them just by applying the settings you see right here on the screen. Anyway I'm going to cancel out. And tell you what, this is a pretty good automatic color correction, I would go so far as to say. But let's try something different without completely ruining our previous settings. So let's just go ahead and turn the old adjustment layer off, so that it's sitting there waiting to be used again. The great thing about the adjustment layers, as I mentioned this earlier in my Fundamental Series, but notice down here in the lower left corner of the image window, we'll see Doc is 9.79M flat, and then we see a slash, and it's also 9.79M including layers.
So the adjustment layer doesn't take up any room, and when I say it doesn't take up any room, it takes up a few bytes of data, and bytes are little bitty bits of data. They are eight bits of data a piece actually. But they are nothing compared to kilobytes and kilobytes are nothing compared to megabytes, which are nothing compared to gigabytes, and terabytes, and all the other things that will bite you. So anyway, I'm just saying that these are really tiny and you might as well just keep them. So keeping old unused adjustment layers is just fine and actually a good practice. So now I'm going to go back to the Adjustments palette, this whopping big palette that is taking up so much space on my screen, which I resent, by the way, I should just say this very quickly.
Notice this big empty space down here? The reason we are seeing this big empty space down here is because the Adjustments palette is always set to consume as much space as the biggest adjustment, which happens to be Curves. So the Curves Adjustments as we'll see will take up this entire region, but Levels doesn't. I wish this darn thing was smart enough to collapse if we don't need the unused space, because Layers are getting squished down here, and they are going to get even more squished in just a second, but not the way things are working out right now. So I'm going to click on this green arrow right there, to return to my Adjustments list, and then I'm going to Alt+Click or Option+Click on this little levels icon right there and by the virtue of the fact I have the Alt or Option key down, Alt on PC, Option on Mac, I'll bring up the New Layer dialog box, and I'll call this Composite histogram modification, but that's implied, I'm not going to type that in there.
Then I'll click OK in order to create this new Composite histogram levels adjustment and notice that my image itself is rolled off the bottom of the Layers palette, because this big monstrous Adjustments palette is squishing it, but it's still there of course, it's still down there. Anyway, got this Levels adjustment selected, and now let's focus our attention on this middle region right here, which contains the histogram itself, and these three values below the histogram which are the input levels.
I should say whether you are working within adjustment layer the way we are, or a composite levels modification, then you are going to see a histogram, and you would see that if you are working with a composite modification, by which I mean a static modification, that's what I meant to say. If you went and applied, for example, under the image menu, you went to Adjustments and then you applied the levels command, which I can't right now, because I have an adjustment layer selected. But if you went that route, you would still see a histogram inside the Levels dialog box, and you would see these three values right here. So everything works the same, and what we are saying, this histogram, I was saying way back in Chapter 5 of the Fundamental Series, I was telling you that this histogram is a bar graph, of all the luminance levels which are the little brightness values, the luminance levels inside of the image, from black, over here on the left all the way over to white, over here on the right. This graph when you are looking at the expanded view of this palette, which we are, and you can switch between the two.
You can switch between the itsy bitsy standard view, which is squished. It unsquishes the Layers pallette, but squishes the Adjustments palette which is no good, and of course the expanded view which is better by clicking on this little folder icon right there. When you are working in the expanded view, the histogram is exactly 256 pixels wide, which is important, because there are 256 different luminance levels per channel inside of a standard 8 bit per channel image, which is the way that JPEG images for example are saved, all JPEGs are saved that way, JPEG, RGB images.
Anyway, notice these values underneath the graph, 0 represents black, and this first value corresponds to the little black slider triangle, and this last value here, the third value, corresponds to the little white slider triangle, and it's 255, which is the luminance level for white. Now I was telling you there are 256 different luminance levels, and this tends to confuse people, why is white 255 and black is zero? 255 plus zero does not equal 256, where did the last guy go? Well it's black, So in other words, here's how it works. One, there is a brightness value right next door, right, if I were to move this over just ever so slightly, just one pixel over, there is the brightness value of one, which is a very dark color, not quite black, but very dark. So you got one going all the way over to 255, so those are your first 255 different luminance levels, plus you've got yourself black, which is represented by the number zero, but it's still a distinct value.
So you don't add zero, you just add one more value for black and you would get 256 different variations. So if I were to work with this graph here, if I were to drag the black slider over to the right, until I get an initial input levels value there of 12, then I'm saying, anything with a luminance level of 12 or darker is going to get clipped to black, and that is going to then spread out my histogram over the remaining area. This might make even more sense if I were to take this white slider triangle, and notice how it's communicating its information here with this third numerical option there. If I drag it over to 192, let's say, then I'm saying anything with the brightness value of 192 or brighter is turning white, and that's going to stretch this remaining area here, this histogram across the entire histogram space.
So in other words, we are increasing the contrast of the image, and you can see that actually happening here inside the image window. See this guy right there, this little option right there; if I were to click and hold on it, then I'll see the default version of the image, with the current adjustment turned off. So it temporarily turns off the layer, and then if I release, I'll see the corrected version of the image. So in other words, click and hold for before, release for after, and you'll notice there's a little keyboard shortcut associated with it, that's the Backslash key, and if you press and hold Backslash, you may have luck with getting this to turn off for a second and then release Backslash again to see the after version of the image.
However, if I were to do it right now, it would try to enter a backslash character into this little highlighted option, and so let me see if I can click on something else here, like this RGB Channel option, and then I'll press the Esc key. Now let me see, if I press and hold the Backslash key, now it's working. So I'll press and hold Backslash in order to see the before version of the image, so it's press and hold, and then release in order to see the after version. So I'm just letting you know it's there, because you might see the tip. I don't really think much of the keyboard shortcut, because it frequently doesn't work, because one of the numerical options is highlighted and it's preventing it from working, and that can be a pain in the neck, but it's there.
I just want you to know it's there. By the way, notice that I kind of moved the black slider triangle to the beginning of the humpolumpolas of the histogram here, and then I move the white one to the end of it. So that we're tucking right next to the mountainous region, and that's pretty standard behavior, that's kind of what you typically want to do. And when I say kind of typically, I mean almost always, but I'll show you a few more nuanced approaches as we get further into this, but I just wanted to give you a sense of kind of what you tend to do when you are approaching this histogram.
In that way you are just clipping the dead stuff down here. So you are clipping away the dead grass, as it were, down here in the plains, the low lands. So many analogies I can share with you that aren't really serving you any good. So now, in between the white point and the black point is this gray point right here, which is the gamma value. Notice that it's represented totally differently. It represents that middle gray which if you divide 255 by 2, you would either get like 127 or 128.
So you would think maybe that's how they would represent this value right here, but instead it's 1.0, because it's an exponent, and I'm going to explain how this function works, this gamma value, because it's very, very important to correcting your images. We are going to spend a little time with it in the very next exercise.
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