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The elusive alpha channel remains one of the most misunderstood yet powerful tools in Photoshop. Alpha channels are collections of luminance data that control the transparency of an image, and they inform just about every aspect of Photoshop. As he builds transitional blended layers, fashions a depth map, makes edge adjustments, and takes on extreme channel mixing, Omni Award-winning expert Deke McClelland teaches Photoshop users that where there's a will, there's a way. Photoshop CS3 Channels and Masks: Advanced Techniques covers mapping texture on an image, turning flesh into stone, using vector masks, working with all different channels, creating a rustic edge effect, and much more. Exercise files accompany the tutorials.
Download Deke's customized keyboard layouts for Channels and Masks from the Exercise Files tab."
In this exercise, we are going to explore the creation and use of a corrective mask inside of Photoshop. In this case, we want to use the corrective mask to correct wayward hues inside of this face here. This happens to be a photograph of my son, Max, that I shot years ago, now using a low end camera. The name of image is called Average hue.tif, it's found inside the 12 Speciality folder. Now the reason that we have all these wayward hues inside of this image, it's not a function of the actual colorization of my son's face, you will be glad to know but he doesn't simultaneously have these hot pinks and these weired yellows going on inside of this flush. This was a bad reaction on the part of the camera. However, you might be trying to solve for the camera or for real weired skin tones. Either way, the technique that we are about to explore will work for you.
So here is want we are going to do. First, we are going to go over to the Channels palette. Notice that I have an RGB image, of course. I also have a final version of the mask that we are about to create here. I want you to go ahead and grab one of the channels and the best channel, I think, in our case is going to be the Red channel since this a portrait shot. You can explore the others, if you want, but I am just going to go ahead and grab that Red channel and make a duplicate of it by dragging it down to the little Page icon here at the bottom of the Channels palette, and I am going to rename this channel, mask, because that's what it's going to be.
Now with this mask channel selected, I am going to go up to the Image menu and I am going to choose Adjustments, and instead of choosing the Levels command, I am going to choose the command that's going to go me a little bit more control over the process of increasing the contrast of the image, and that's this one right here, Curves, which you can get to you by pressing Ctrl+M or Command+M on the Mac. Ir brings up the revamped Curves dialog box here inside Photoshop CS3. I want many of my dark colors to be mapped to black. So I am going to take this black slider triangle and I am going to drag it over to about 64. So we are taking everything that has a brightness value of 64 or darker and making it black. Then I am going to click to create a point right here, roughly, inside of my line and I am going to drag it up so that the Output level value is about 140 and the Input level value is about 115.
By the way, you can nudge these values from the keyboard. So if you press the Left or Right Arrow key, it will change the Input level value. If you press the Up or Down Arrow key, it will change the Output level value. So this is what we want, 115 Input, 140 Output. That means we are taking every thing that used to be 115 and we are changing it to 140. So we are brightening those mid-tones. We could have done something similar using the gamma value inside the Levels dialog box. The fact that we are doing it inside of the Curves dialog box, this gives us a specific control over where that gamma location is. So we are supposed to put in the gamma location in the middle directly between the black point and the white point. I am able to shift it over toward the black point a little bit.
Now I am going to go ahead and click OK in order to accept that modification. At this point, we need to do a little adjustment using an Overlay Brush. So I am going to go ahead and zoom in. Now bear in mind, these are flesh rounds right there and right there, those are part of Max's neck so we need to retain those areas. So I am going to de-select the image, grab the Brush tool, switch to the Overlay mode by pressing Shift+ Alt+O or Shift+Option+O on the Mac, and I am going to start by painting with white. So I am going to press the X key to make sure that the foreground color is white and then I am going to paint over these areas, just one brush stroke a piece.
Then I am going to press the X key to switch black to my foreground color here and I am going to paint inside the zippers in order to paint some of those highlights away, as much as I can, actually, which isn't all the way gone but it's pretty well gone. Now I will increase the size of my brush and paint this area in order to paint that away. I don't want to paint too aggressively, I don't want to get rid of that little tiny area flesh so I will take it easy. Now this area right here is part of his blanket. So it is something that you want to paint away. Now I am going to go ahead and select these regions using the Lasso tool, like this, in order to just -- I am just dragging around trying to get these areas as well as I can, and I will select those, and then I am going to select up and around here and through here, and just grab this region, and fill it with black by pressing Alt+Backspace or Option+Delete.
A few other areas that we need to address; I will go back to my Brush tool here. I deselect it, by the way, the image by pressing Ctrl+D or Command+D before I start brushing again. I am painting these areas around his ear and cheeks away and that should be pretty darn good, I think. Now I am going to zoom out and it's okay, we have some dark areas around his cheek that I just painted. You can get rid of those, if you care to, by pressing the X key and painting with white, like so. But I don't want to flatten out that cheek too much. So I am going to undo that modification. Maybe switch the Opacity to 50% by pressing the 5 key and painting again. So just a little bit of lightness in here. I actually like these gray contours, it work for us. So we don't want to delete those entirely.
Go ahead and switch to Lasso tool now and just, kind of, Alt+Click around this region, Option+Click on a Mac and of course, in order to draw a big polygon around his head. Then I am going to press Ctrl+Shift+I or Command+Shift+I in order to reverse the selection, that's the same as choosing the Inverse command from the Select menu. My background color is currently black so I will just press the Backspace key or the Delete key to fill in that region, outside of his head, with black. Now I will press Ctrl+D, Command+D on the Mac in order to deselect the image.
We have managed to create the mask. You can see that it's a lot like the mask that you just got done created or at least the one I just got done created, it looks a lot like the one that I have stored inside of the Max mask folder. So you have got a mask, you can either use the one that you created or you can use the one that I created for you. Either way, we will be employing that mask in order to smooth away the aberrant colors inside Max's flesh, in the next exercise.
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