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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.
In this exercise I'm going to show you how to change the color of the mask overlay that you see when you're viewing the mask and the image at the same time. I've saved my progress as First tentative edit.psd. I have the boot channel selected. We are viewing the RGB image at the same time. Now as I was telling you, this red overlay is based on the old Rubyliths that many of us used in the precomputer days. The color works well for some images, not so well for others. In our case it's hard to tell what's going on, because the shade of red assigned to the mask, very nearly matches the red of the boot.
So here is how you go about changing the color. You go to the Channels panel and you double-click anywhere on the alpha channel, and then you'll see that you have this color swatch. Go ahead and click on it to bring up the Color Picker dialog box. And let's dial in a complementary color, and, by the way, when you're modifying the Hue value, you can find the color complement of any other Hue, just by adding or subtracting, whichever is easier, 180 degrees. So in our case, we changed the Hue value from 0-180. That gives us this bright Cyan.
Click OK, and then you have to decide what level of Opacity you want. Now unfortunately we are not able to preview our changes to the mask overlay, so you are kind of working blind. I'm going to go ahead and take that Opacity value down to 20%, click OK. That's not nearly opaque enough, so I'll go ahead and double-click again, to bring back the Channel Options dialog box, and let's try an Opacity value of 35% let's say, and click OK, and that looks a heck of a lot better. Now if I were to select a region and fill it with the foreground color white, by pressing Alt+Backspace or Option+ Delete on the Mac, then I would fill it with transparency, just as before.
If I instead, I'll go ahead and press Ctrl+Z or Command+Z on the Mac. If I instead press Ctrl+Backspace or Command+Delete on the Mac to fill the selection with the background color black, then I'd end up adding to the cyan overlay. All right! I'll go ahead and press Ctrl+Z or Command+Z on the Mac to undo that modification as well. Note that this is a channel by channel attribute, so the color overlay actually gets saved along with the file. If I turn off the eyeball in front of boot, and then I turn on the eyeball in front of nameplate, notice that nameplate still has the default ruby overlay, which is actually really great, because it means that if I turn on both channels at the same time, I can tell the two channels apart.
Here's something that's really interesting I think. I don't necessarily ever take advantage of this, but it is there and you do want to be aware of it. You can select two channels at the same time by clicking on one and Shift+Clicking on the other. So I now have both alpha channel selected, and I can go ahead and select a portion of the image, and let's say, I press Ctrl+Backspace or Command+Delete on the Mac in order to fill that area with the background color which is black. I add blackness to both of the channels. So you can edit the contents of two channels at the same time in Photoshop, which is utterly and completely remarkable in my opinion, because you can't do that with layers, you can only edit a single layer at a time.
I certainly don't want to do that of course. So I'll press Ctrl+Z or Command+Z on the Mac, just want you to note that that is an option. Then I'll go ahead and click on boot to select it independently. So I don't end up harming the nameplate layer. I'm going to go ahead and turn it off as well. A couple of other things to note. If I press the tilde key to turn off the RGB image, so I'm viewing the mask by itself. Notice the little default color swatch down here at the bottom of the toolbox, the one that you get by pressing the D key. Notice it changes the foreground color to white and the background color to black.
However, if I press the tilde key again, so I'm viewing the color composite image. Then you'll see now the little default color swatch changes the foreground color to black and the background color to white, and that's just something to bear in mind. So if I hit the DekeKey now, I'll get black as my foreground color. I am not sure I'm able to defend Photoshop's reasoning where that's concerned, however, that is the way it is. One more thing to note here. I'm going to double-click on the Channel to once again bring up the Channel Options dialog box. Notice the Color Indicates options here. In addition to Masked Areas, so in other words, the cyan overlay is coding the masked regions of the image.
You could invert that. You could say no, go ahead and cover up The Selected Areas instead, click OK and now you have a different view into your image, which means that the whole equation flips upside down. So in other words, if I select an area and press in this case Alt+Backspace or Option+Delete to fill that area with black, meaning cyan overlay, then I'm adding to the selection. I'll go ahead and press Ctrl+Z or Command+Z on the Mac, where I too instead select an area and press Ctrl+Backspace or Command+Delete on the Mac to fill it with white, that is transparency, then I'm deselecting.
Now between you and me, I've been masking for years ,and as soon as I start trying to invert the equation, I get terribly confused. So I don't work that way. I'll press Ctrl+Z or Command+Z on the Mac to undo that modification. I stick with having the color indicate the Masked Areas, otherwise, I just can't keep track of what I'm doing, but it is an option. Your brain may well work differently than mine. Finally, you can go ahead and convert the layer to a Spot Color. That takes you into a whole different arena. So in other words, it's not an alpha channel anymore. It's now a color bearing channel that will communicate in actual Spot Color with the image.
Obviously, we're not going to do that. So let's stick with Masked Areas, click OK. We'll get back to our familiar, in this case, cyan overlay. In the next exercise, we'll use this overlay in order to modify this mask and make it exactly match the contours of the boot.
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