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Photoshop Masking and Compositing: Fundamentals is the introductory installment of Deke McClelland's four-part series on making photorealistic compositions in Photoshop. The course shows how to make selections, refine the selections with masks, and then combine them in new ways, using layer effects, blend modes, and other techniques to create a single seamless piece of artwork. Deke introduces the Channels panel and the alpha channel, the key to masking and transparency in Photoshop; reviews the selection tools, including the Color Range tool , Quick Mask mode, and the Refine Edge command; and shows how to blend masked images so they interact naturally.
All right after that initial look at color channels it may seem downright peculiar that the one thing that these channels aren't is colorful. After all if you view any of these channels independently red, green, or blue, you're going to see what it's functionally a grayscale version of the image and there's really no way to reconcile the notion that somehow three grayscale images mixed together create a full color composite, things may seem stranger still. When I demonstrate that if you view two channels at the same time they are back to being in color, so if I go ahead and click on the eye in front of green then we can see how the green and blue channels mix, but as soon as I turn green off by then we go back to this very dark almost inverted grayscale image.
I can turn the red channel on and we'll see how red and blue mix together, then if I turn the blue channel off I'll end up seeing that grayscale red image by itself and then if I turn green on we can see how red and green mix together, we get those bright yellows as you can see. In fact, the lightest color we see at this point is yellow which we're seeing inside the text. The red and green channels, by the way, carry most of the color information; the blue channel makes the least amount of difference on its own. However, in our case it's very important for communicating the background colors and without blue we don't get nice bright whites.
All right, I'm going to switch back to the RGB image. The thing is while these grayscale views of the channels are extremely useful to us as we create masks they are not the way that Photoshop actually sees the channels. I'm going to switch back to the Layers panel and I'm going to turn off those two groups because we don't need to be seeing all those labels. And then I'm going to go up to the Edit menu. If you're following along on a Mac you would go to the Photoshop menu and then go all the way down to the Preferences command. It's not that far down the list on the Mac and then choose Interface.
And notice since I have the Interface panel there is this check box, it's turned off by default, Show Channels in Color, go ahead and turn it on and then click OK. And now if you switch back to the Channels panel you'll see your thumbnails rendered in color because this is the way things really work. If I click on the red channel you can see that the darkest pixel in the channel is black and the brightest pixel is full on red, and all the other pixels are different brightness variations of red. The same goes for green and blue, so if I click on the green channel the darkest pixel is going to be black, the brightest pixel is going to be a very bright shade of green, and then all the other pixels are different shades of green, you'll notice, by the way, that green is your brightest channel and blue is by far the darkest channel.
So the darkest pixel once again is going to be black, the brightest pixel is going to be that deep shade of blue and all the other pixels are different shades of blue. Now at this point I think you can get a sense for why this is not the default setting inside Photoshop because it is almost impossible to evaluate the blue channel when it's colorized, and it remains difficult to evaluate even the brightest channel green and red as well, which is why Photoshop goes ahead and shows you those channels as grayscale images by default.
All right, I'm going to switch back to the RGB Composite. In the next exercise I'll demonstrate how Photoshop mixes the red, green, and blue channels together.
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