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In this exercise I am going to show you a little-known trick for previewing exactly which pixels inside of an image are clipping to either black or white on a channel by channel basis when you adjust the black-and-white points here inside the Levels panel. I saved my changes from the previous exercise as Open shadows.psd just in case you want to compare my file to yours. Now I am going to switch over to this one. It is called Levels set to Auto.psd. It is the result of our noodling around with the Auto button a few exercises back now. Let's say that I want to go ahead and wipe out the changes that I've made here inside the Levels panel so that I can start afresh.
I don't want to get rid of the Adjustment layer; I want to keep it because I need it. I just want to start over again. All right, then notice I have this icon down here in the bottom-right corner of the panel. You can see that the arrow goes all the way around the circle. This icon actually has two states and let me show them to you. I am going to go ahead and change the Gamma value to let's say 0.7. I am not recommending this change; I am just doing it for the sake of demonstration. Now notice that this cursor down here in the lower-right corner only makes it halfway around the circle and the hint says, reset to previous state.
So if you click on it, then you're going to get rid of your most recent modification and now the arrow goes all the way around the circle, click again, and you will wipe out all the changes that you've made. For our next modifications to work, I really need the Opacity value to be set to 100%. So I am going to press the 0 key in order make it so. So now we have a fully opaque version of this Adjustment layer. It doesn't happen to be doing anything right now, but it will in just a moment. So check out what happens when I modify the Y point value.
Let's say I take it down to what is it now, 224. I know just because I know how the dialog box works that any pixel with a composite luminance level of 224 or lighter is going to get clipped to white. But what does that mean inside the image? I don't know where these pixels are located. In other words, just because they appear over here on the right-hand side of the histogram doesn't mean that they're somehow magically over on the right-hand side of the image. Those clipped white pixels could be anywhere inside the image. The same holds true if I were to clip all the pixels that have a luminance level of 68 or darker to black.
Again, I know the effect that it is going to have on histogram because it can bring up the Histogram panel and there it is. Lots of pixels are getting clipped to black and white as indicated by those tall lines on either side of the graph. But where they are inside the image, who knows? Well, you could preview which part of the image is being affected by pressing-and-holding the Alt key or the Option key on the Mac, and then dragging either the White or Black slider triangle. I am going to start with the white one because it is a little easier to understand. Now notice as I Alt+Drag or Option+Drag this White slider triangle, I am going to see the clipped pixels onscreen.
But in order to read this, you need to know what the various colors you're seeing mean. Black means not getting clipped. It is perfectly fine. White means, it is getting clipped in all three channels. So that's very dangerous, especially if you're seeing big areas of white. That's no good, you don't want to clip huge areas to white inside of an image. If you're seeing any color, that means it is clipping inside of that channel. So where we are seeing red, it is clipping inside the red channel. Where we are seeing yellow, well there is no yellow channel inside of an RGB image. So that's a combination of clipping occurring in both the green and red channels at the same time.
In other words, in those yellow regions we only have blue detail and nothing more. Then if I were to release, then I will see the clipping actually taking place inside of the composite image. All right! So that's what happens when you Alt+Drag or Option+Drag the white triangle. When you Alt+Drag or Option+Drag the black triangle, things turn on their heads, so you get an inverted picture. Wherever you see white means no clipping is occurring. Where you see black means it is clipping in all three channels, and wherever you see another color is the invert of the channel in which the clipping is occurring.
So yellow for example means that we are clipping in the blue channel, red means we are clipping in a combination of both the blue, and the green channels, because the opposite of red is cyan, and cyan is combination of blue and green working together. So that just gives you a sense of what's going on. Again, what you want to do is avoid big areas of black. So tiny areas of black like this are going to be fine, but big areas of black like this are no good. Well, in my case what I can see here is that a value of 60 works out pretty nicely for closing in on those eyes.
I'd go ahead and Alt+Drag or Option+Drag the White slider triangle all the way up to the right because otherwise I am starting to clip details in a way I don't want. So we really don't want to clip anything over there on the right-hand side of the graph. So this is a good starting point. In the next exercise I will show you how you can set the black point, the white point, and the gamma using these three eyedroppers.
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