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There's nothing people love more than lists, and Photoshop Top 40 offers a great one, highlighting the best features in Photoshop. Deke McClelland counts down to #1 with a new video each week, detailing one great feature after another in this popular digital imaging application. The videos cover tools, commands, and concepts, emphasizing what's really important in Photoshop.
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(Music playing) Deke's Photoshop? Deke's Photoshop? Top 40! #9! Feature #09 is Levels and by association its partner in crime the Histogram. The Levels command allows you to adjust the luminance levels inside of an image on a channel-by-channel basis. The practical upshot of which is that you can enhance the contrast of an image as well as correct for color cast. Now, in many ways Levels is a leaner meaner version of feature #24, the Curves command, and while strictly speaking Curves is a more powerful feature, I favor the Levels command because it tends to be a more efficient experience, as we will see.
Now I am going to start things off by showing you how to read and respond to a Histogram, which is an absolutely essential skill inside of Photoshop. We are seeing on screen a gradient that proceeds from violet over here on the left-hand side to a pale yellow on the right-hand side. Let's see what's going on with the luminance levels on a channel-by-channel basis inside of this RGB image. So I have switched over to the Channels palette, I will click on the Red channel, and we see the gradient represented by dark grey over here on the left-hand side, and white over here on the right-hand side.
In the Green channel, things darken up, so that we have black over here on the left-hand side and a light grey over on the right-hand side, and then inside the Blue channel, we get less contrast. We have got a dark grey on the left and a light grey on the right. All right! Let's see how that looks to a histogram. Inside of Photoshop I am going to switch over to the Red channel once again, go to the Image menu, choose Adjustments and choose Levels. Now we will see an application of the Levels adjustment layer in just a moment. But for now, I am going to apply a Static Levels adjustment, which you can also access by pressing Ctrl+L or Command+L on the Mac.
That brings up the Levels dialog box, front in center right there is the Histogram. The Histogram is a bar graph of the luminance levels inside of an image starting with black on the left-hand side and white over here on the right-hand side. The numerical value for black is 0 incidentally. The numerical value for white is 255, just something to bear in mind. Now in our case, we are seeing that we have some fairly dark colors and then we have lots of light colors over in this region, and the light colors by the way inside of Photoshop are known as highlights.
So generally speaking, light colors are known as highlights, dark colors are known as shadows, and then everything in between is known as mid-tones. But we are ultimately lacking shadow detail inside of this channel. There are no really dark colors here. In fact this guy right there is the darkest color inside this channel, and that corresponds of course to this dark color over on the left-hand side. Now you are not normally going to see your dark colors on the left, and light colors on the right inside of the image, they are going to be scattered all over the place. But you are always going to see the dark colors on the left-hand side and the light colors on the right-hand side inside the histogram. All right! I am going to cancel out of there.
Let's switch over to the Green channel. I just want you to see what these various histograms look like. I will press Ctrl+L, Command+L once again on the Mac. And notice this time we have plenty of shadow detail. So we have got absolute blacks going on inside this histogram, and we have got lots of mid tones. We do not have any white, no sign of white inside the histogram, and sure enough, there is no sign of white inside of the Green channel, and we are missing highlight detail in general. All right? Cancel out of there. Let's check out the Blue channel, Ctrl+L, Command+L once again, and this time everybody is right there in the center.
All we have is mid-tones, we have no highlights, we have no shadows. All right, so what do we do about that? Well I am going to cancel out of this dialog box once again, switch over to RGB, so that we have access to all three channels at once, and I will press Ctrl+L, Command+L on the Mac and now we have this composite view of all of the histograms inside the image, which produces this kind of crazy pagoda right there. We are not going to make any changes to that pagoda. Instead we are going to switch between the Red, Green, and Blue channels.
So I am going to start with Red and I am going to take this black Point slider, and I am going to move it up till that first value changes to 60, as we see it right there, it's now highlighted. In this case, I am seeing anything with a Luminance level of 60 or darker is going to become black. That makes the darkest color inside the channel, black stretches out everybody in between, leaves white set at 255. So we are not tampering with white at all, but everybody else gets stretched out. And that makes the composite image darker on screen as well and it changes the nature of that dark color from violet, as it was before, to something of a very dark blue now, kind of an indigo. All right! I am going to switch over to Green, and this time we are not going to tamper with the black value, we are going to leave that alone, but we are going to modify this white point.
So I will take it over to 220 that is the final value right there, which is now highlighted, is going to change to 220. So I am seeing anything with the Luminance level of 220 or lighter becomes white, which is 255 of course. Everybody else gets stretched out in between. Now notice that I have a more highly saturated yellow over there on the right-hand side, and that lightens the image overall. Now, I am going to switch to the Blue channel, and this time I am going to take the black point up to 60, so that it becomes absolutely black and I am going to change the white point value to 170, so the lightest color becomes white.
Notice what has happened to the composite image, not only have I enhanced the contrast of this image so that the gradient begins black and ends white but I have also neutralized the color cast. There are no colors going on inside the image at all. Now by neutralizing colorcast inside of a continuous toned photographic image, I don't mean converting it to grey scale. I just mean getting rid of wrong colors inside the image. But this happens to be an exaggerated example that we are looking at on screen right now inside this gradient, renders the entire thing grey.
Isn't that interesting? Then if I switch back to the RGB view, you will see the dynamic histogram. So the histogram has been updated inside the composite view so that we can see the changes that we brought inside the image. Now the final slider right there, that grey one is the so-called Gamma value, and what it allows you to do is darken or lighten the mid-tones. So if I drag this grey slider over to left, notice that in the case of this gradient, I am actually moving the mid point over to left-hand side.
So I am compressing the shadows. I am enhancing. I am stretching out the highlights there by lightening the image over all. If I were to drag this grey slider over to the right, I would compress the highlights, I would stretch out the shadows and I would darken the image overall by moving that mid point to the right once again. Now, were I working inside of continuous toned image, I am not going to be moving midpoints to left or to the right, but I am going to be respectively lightening or darkening the mid tones. Let's cancel out of there, and let's switch to a real honest-to-gosh continuous tone photographic image, like this one right here, which happens to come to us from a group called Photo CD that sells its wares through the Fotolia image library.
Now I should mention that I have gone ahead and exaggerated the problems that were inherent with this image. So it did have a little bit of red color cast like we are seeing right here, and it was a little bit low contrast. But I have taken those two slight problems and turned them into huge problems for the sake of demonstrational purposes here. I am going to switch over to the Layers palette and I am going to expand my Adjustments palette, and then I am going to go ahead, and Alt+Click or Option+Click on this little Levels icon right there in order to bring up the New Layer dialog box, and I will call this new layer Contrast & Color Cast because we are going to be fixing both problems in one fell swoop.
I will click OK and now I have created a new adjustment layer here inside of Photoshop. Now, I can go ahead and adjust my composite histogram. Notice that I am seeing a histogram here inside the Adjustments palette. I am also seeing a big histogram, this is very important. If you are seeing a tiny histogram like so inside of Photoshop CS4, then I want you to go down to this little Folder icon with the arrow on it and I want you to click on it in order to expand that palette, so that you can see a full size histogram right there. So in this case we have got lots of mid -tones indicated by that big mountain there, a fair amount of highlights and very little in the way of shadows.
So let's fix that by dragging this black slider over to the right-hand side. In this case I am saying for example, that anything with the Luminance level of 53 or darker is becoming black which does add shadow detail inside of this image. So we are definitely darkening up this otherwise washed on image. The problem is we are not correcting for the colorcast. So if you change your composite histogram, you are not going to make any modifications to the colorcast of the image, only the contrast. If you want to fix contrast and color cast all at once, then you need to apply your changes on a channel-by-channel basis.
So I am going to go ahead and restore this black point value to 0, and I am going to click on this little pop up menu here and I am going to switch over to the Red channel and then I could drag this black point like so over to the right-hand side. Now here is something that I originally showed you when I was demonstrating feature #12 Camera Raw inside of Photoshop. If you press and hold the Alt key or the Option key on the Mac and drag this black Point slider, you can see a preview of those colors that are going to get clipped. So anything that appears black inside of this channel is going to get clipped to black, anything that appears red, where this channel is concerned because we are looking at the Red channel is not going to be affected at all.
Compare this, by the way, to what happens if I were to Alt+Drag or Option+Drag the white slider triangle. Anything that's changing to red will get clipped inside of this channel. Anything that's appearing as black will not get clipped. That's just something to bear in mind. You can Alt+Drag or Option+Drag either the white slider triangle or the black slider triangle on a channel-by-channel basis, as well as in the Composite view. But you know what, there is yet another way to work. Instead of going in to every channel and modifying each one of these black and white slider handles independently without any guidance whatsoever, you can get some guidance from Photoshop by clicking on this Auto button.
If you just go ahead and click on Auto, then Photoshop will apply what's known as the Auto Levels command, in which case it's going to automatically adjust the black point and the white point, not Gamma but just black point and white point on a channel by channel basis and we end up getting this effect right here. So while this is not exactly the modification I want to apply, we are already much closer to our final results. Now at this point, I can tweak these settings. For example, I am going to move this black point down to 60. So I am seeing anything with the Luminance level of 60 or darker inside the Red channel is going to be made black.
Now, I am going to switch over to Green, and this time I am going to reduce this black point value to 40. So I am easing up on it a little bit. So that I am seeing anything with Luminance level of 40 or darker is becoming black. You know what? I am going to go ahead and slightly raise this Gamma value to 1.05 and that's just going to breathe a little bit of life into the mid-tones inside of the Green channel. And I am going to switch over to the Blue channel. Notice that I am not changing the white point at all inside of any of these channels because that was fine.
I am going to reduce that black point value to 35 in this case, and then I am going to take this Gamma value up to 1. 1 and notice how that adds a little bit of blue to the image and does a great job of compensating for what was previously a pretty heavy red color cast. So now let's take a look at what things look like before the application of this adjustment layer. This is the original version of the image as I exaggerated its problems of course. This is the corrected version of the image, thanks to an application of the Levels adjustment layer which has corrected for contrast and color cast inside of this image.
Now one more thing I want to do. I want to bring out some of the saturation inside this image, so the colors are kind of muted. I am going to do that by adding one more adjustment layer. I am going to click on this left- pointing arrowhead in the bottom-left corner of the Adjustments palette. And then I am going to go over to this guy right there Vibrance and I am going to Alt+Click on it, Option+Click on the Mac, and I do that every time just because I want to name these layers as I create them. I am going to call this Up Saturation or something along those lines, and click OK. Now I am going to raise that Vibrance value through the roof to +85 actually, and then I am going to take Saturation up to +20 so that we can really breathe some life into those colors.
Now I am going to collapse the Adjustments palette and let's do a big before and after now. This is the image as we saw it when I first opened it here inside of Photoshop and this is the modified version of the image, thanks to a combination of Levels mostly. We also added a Vibrance adjustment layer. Very powerful feature, Levels combined with the histogram here inside Photoshop.
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