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If in your workflow you're starting off in Bridge with your RAW files and you're taking them through camera RAW, you want to make sure you're making all of your global adjustments to the tonality and color there before you actually open them in Photoshop. But often I'll find that I need to make a small adjustment as I'm refining my image in Photoshop which I can quickly take care by using an adjustment layer. As we've seen, these adjustments can affect the entire image or only a small portion. In this example we're going to add a Levels Adjustment layer.
And I'm going to go ahead and apply it to the whole image, in order to explain what it's doing. So from the Adjustment panel I'll click on the second adjustment, this is the levels adjustment layer, and we can see that we have a preview of the histogram of the image. So the histogram is just a visual representation of all of the different pixels in your image. And your darkest pixels would be down here on the left hand side and then it would move toward your shadows and in your midtones. Your highlights and then over here on the right are your whites. I can tell by looking at this histogram that I don't actually have any black values.
There's nothing in this image that is pure black, and I know that, because there aren't any pixels being plotted in this histogram. So in order to make sure that this image expands across the entire dynamic range all the way from black to white. I'll want to move over this slider to the right. Now as I move it over you can see that the darker values in my image are getting darker. If I move it too far then I'm going to force some areas in my image to be a pure black. So I don't want to go that far. So I'll back off a little bit.
But what I don't know is exactly where in my image these dark values are. So what I can do is hold down the Option key on the Mac or the Alt key on Windows. And then as I drag this slider, Photoshop will start giving me a preview of those pixels in my image that are being clipped to pure black. And it actually does this on a channel-by-channel basis. So, we know that our photographs are made up of three different channels. There's a red channel, a green channel, and a blue channel, when we're in RGB.
Well, the way that it's being displayed here in the image area when I have the Option key or the Alt key held down, is that if the values are clipped in the red channel, the color will display in red. And if the channels are clipped in the green channel then they're displayed in green and the same if they're in the blue channel, they'll be displayed in blue. But then we have this yellow and magenta and cyan overlay. So that just means that there are pixels that are being clipped in more than one channel. So for example, if you see yellow up here, that means that the red and the green channel are clipped. If you see magenta, it means the red and blue channel is clipped. And if you see cyan, it means the green and blue. And the reason that I point this out is because it's not until you actually see black.
That you're clipping to pure black, so see in the base of the tree there where everything's black right now? That's telling me that everything there will be pure black. Of course that's an aesthetic choice, right? if I let go of the option or the alt key and we look at this I could aesthetically decide that yes I want the tree black but I don't think I do. So I'm going to hold down the Option key or the Alt key again and I'm going to drag this slider until I don't see any black in my image, because that means that there are no pixels being forced to pure black. There can be some yellow in there, there can be some red in there.
As long as there's no black then I know that I'm not forcing anything to pure black. Because when I do that of course, I'm getting rid of detail in the shadow areas. All right now I can also tell that there's a gap in my histogram between this value and the brightest value. So I'll scoot over the white point here by moving this white triangle to the left. Again if I move it to far you can see that I'm pushing pixels in my image to pure white. So let's back off on that. And again, I could hold down the Option key. In which case we're kind of seeing a reverse mask.
And as I drag over to the left you can see those areas that start getting clipped. And if I go far enough, sure enough, big areas start getting clipped to pure white. I just need to back off on that until I don't see any white pixels being clipped. And this really is important, because when you print an image, the image is made up of a bunch of little dots. And our eyes are highly sensitive to patterns and so our eyes immediately see those dots. If you have a photograph that say is a landscape and you got these big puffy clouds in the sky, if you push those clouds to pure white, if there's no detail in them then the printer isn't going to print a dot in that highlight.
And your eye is so sensitive to patterns that your eye will move directly there. Not only because it's the brightest value in the image, but also because it recognizes that there's no dot pattern. So, although you can make an aesthetic choice and push your shadow areas to pure black, it's really not a great idea to push the highlight areas, of your image, to pure white, unless you're going for some type of special effect, like a really high key image. Alright if I want to preview what I've done, I can click the eye icon that toggles the preview on and off. You can see that with it off, I've got a much flatter looking image. The image isn't extended across the entire dynamic range. When I toggle on the eye icon to see the changes, you can see that we've really extended our histogram across the entire dynamic range. Now it doesn't look like we've made a change to it. But in order to show you what's happening to it I'm going to close the properties panel for a moment and under the Window menu I'm going to select the Histogram panel.
So here is the histogram, it kind of looks very familiar. We were just looking at one that was similar in the levels adjustment layer. And if I toggle on and off the Levels Adjustment Layer. There's before. You can see how the histogram doesn't reach all the way to the highlights nor to the shadows. But afterwards, the histogram has been extended across the entire dynamic range. You'll also notice that there are now gaps in this histogram because if I toggle it off, in the before state there was this nice clean histogram with no gaps, but I had to extend it. I had to stretch out this histogram so that I would have a highlight. And I would have a shadow and when I stretched it out, that's what created those little gaps.
Now Photoshop is trying to warn me that this isn't the most accurate view so if I click on the exclamation mark there, Photoshop will rerender the histogram. But I still have those gaps, and one of the reasons that they're so dominant in this image is because it is only an 8-bit image. You can see over here that I saved this file as a JPEG file in 8-bit, but if I were working in 16-bit image, we wouldn't see nearly those gaps there. So you can see how the levels adjustment layer is going to help us to extend this dynamic range. Now, of course, if you're starting in Bridge with a Raw file and you're moving through Camera Raw as part of your work flow, you definitely want to extend the dynamic range there, because that's a lot more nondestructive than doing it afterwards once you've created this pixel-based file in Photoshop. And then go and make changes to it like we just did with the adjustment layer. But it is nice to know that if you've moved on down your workflow, and maybe you don't have the time to go back to the original image, you can make these adjustments here in Photoshop.
And of course, we made it to the entire image. But we could've made a selection, and then only adjusted that select portion of our image as well.
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