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In this movie, I'll introduce you to the three Auto commands. They're all under the Image menu and they include Auto Tone, Auto Contrast and Auto Color. Each one of them automatically adjusts the luminance levels inside of an image on a channel by channel basis. You just choose a command and it does its thing. If you like the result, you keep it, if you don't; you press Ctrl+Z or Command+Z on the Mac and try something else. Now the reason I'm showing these commands is not because they're terribly powerful. Hopefully, you won't be using them that often.
However, Adobe's Click Data--Adobe collects the information from Photoshop users who buy into the program. Adobe's Click Data suggests that these three commands rank among the top 10 used features inside the software. So I'd like you to at least understand how they work. So I've set up this demo that includes a dollar bill. So I've set up a total of four money details, separated on independent layers. The first layer control, which is the guy over here on left, that is the Control layer.
We're not going to change the luminance of that layer at all. So I'll start things off by selecting the Auto Tone layer, which is the image in the middle of the screen here, and then I'll go up to the Image menu and choose the Auto Tone command. Now here's what's going on. Photoshop evaluates each channel independently and makes the darkest pixels in that channel black and the brightest pixels white, and stretches the other luminance levels across the spectrum. And it does so, on a channel by channel basis. So each channel is treated independently.
What that means is you end up changing the color cast of the image. So in our case, we've lost the natural green cast of the image and it's been replaced by a kind of reddish cast in the shadows. So you may find Auto Tone to be useful if an image contains a color cast that you want to get rid of. It's not really the case for this dollar bill however. All right, I'm going to scoot things over, so that I can see the next layer, which is Auto Contrast. I'll go and select that layer in the Layers panel, then I'll go up to the Image menu and choose the Auto Contrast command.
This time Photoshop is making the darkest pixels black and the brightest pixels white on a composite basis. So in other words, all three channels are affected in exactly the same way. That means we get darker shadows and brighter highlights, but the natural color cast of the image is not affected. And then finally over here on the left- hand side, we have the Auto Color image. I'll go and select the Auto Color Layer then go up to the image menu and choose the Auto Color command.
Now what Photoshop is doing is making the darkest pixels black and the brightest pixels white, once again on a channel by channel basis, just as with the Auto Tone command, but it's also neutralizing the midtones. So this is the only Auto Function that changes the midtones inside the image, and what that means is the authentically colorful items, such as the serial number and seal remain in color, but everything else about the dollar bill essentially goes grayscale.
All right I'm going to go and press the F Key a couple of times in order to switch to the Full Screen mode and then I'll press Ctrl+0 or Command+0 on the Mac in order to zoom out and that's what you should expect from the three Auto Commands, Auto Tone, Auto Contrast and Auto Color, found in the Image menu.
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