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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."
Over the course of the next few exercises, we are going to be creating a color mask which allows us to isolate one region of color from other colors inside of an image. Specifically, we are going to be taking this image right here Dry dandelion.jpg which is found inside of the 12 Specialty folder. This image comes through us from photographer Bobby Osborne of istockphoto.com and we are going to take this woman's blouse here which is currently a kind of crimson color and we are going to be shifting it over to yellow. If you know your way around Photoshop, then you know the best command for this purpose is Hue/Saturation, because the Hue/Saturation command allows you to relegate areas of color and then shift them to different colors. The problem is that the Hue/Saturation command works in color blocks and so if a color is found in other areas throughout the image, those areas are going to get shifted as well.
For example, these crimson colors that are showing up inside of her blouse also show up inside of her cheeks, along the sides of her nose, up here on her forehead, all over her lips of course, down her arm, into her fingers, and her shoulders, everywhere that she has flesh. In fact, is basically this same group of colors here. So those colors are likely to shift over to yellow along with the blouse and that's why we are going to end up needing a color mask. What we are about to do by the way, this color shifting inside of fabric is very common in the fashion industry and the catalog business and retail and so forth. You have your four or five colors that a certain outfit is available in, all of those product shots are based on a single shot, they have all been color manipulated.
Often times a color manipulation is to ensure color accuracy so that there are fewer returns, that kind of thing. So this is a pretty good skill to have under your wings here. Now, I can't say that we are necessarily going to feature this image inside of a catalog, but maybe just for aesthetic reasons in our case, we want to change the blouse color. All right. So here is what I want you to do. I want you to create a new Hue/Saturation adjustment layer. So press and hold the Alt key or the Option key on the Mac, click the Black/White icon down here at the bottom of the Layers palette, choose Hue/Saturation. That will bring up the New Layer dialog box. You can now release the Alt or Option key.
Let's call this layer Yellow like so and then click OK. Then, you'll get the Hue/Saturation dialog box up on screen. I want you to shift your edit from Master which changes all colors inside the image. I want you to shift over to reds right here, which you can do from the keyboard if you want to by pressing Ctrl+1 or Command+1 on the Mac. Now, I want you to click some place inside of the blouse in order to establish the base color for this selection. You can Shift+Drag throughout the blouse too if you want to. Although, it may not make any difference to your values that are listed down here at the bottom of the dialog box. These values represent your range.
So basically we would if we started editing here, we would edit all colors that fall between 338 degrees and 8 degrees on the big color wheel. Bear in mind that it switches over from 360 degrees to 0 degrees right there in the middle. Then we are going to have drop offs 30 degrees over to 38 degrees and then 30 degrees the other direction to 308 degrees. Just to give you a sense of where we are on the color wheel, 300 degrees is magenta, and 0 degrees is red. So this is mostly this round between magenta on the purplish side of magenta over to the slightly orange side of red, that we are changing. And you can see that represented down here in the Color Bar.
So these two straight lines here, they represent 338 and 8 degrees. So they represent our absolute region of color changing, and then these triangles represent the drop off zone right there. So I am going to change our Hue value, so that we do some color shifting here. I am going to change our Hue value to 60 degrees, so we are rotating the colors over 60 degrees from crimson to yellow. We are actually a little bit on the orange side of yellow, thanks to the rotation. This is not an absolute value, it's a relative value. So it means that we are shifting all of the colors that many degrees.
Next, I am going to take the Saturation value down to negative10%. So again, it's a relative adjustment. So we are reducing the saturation of all colors that fall inside the zone by 10%. Now, let's go ahead and make some manual modifications. After all, you can see that not only if I turn off the Preview check-box, not only are we changing her blouse, we are also changing the colors inside of her skin tone. So we are making her really yellow. She looks very jaundiced. In fact, I would say she looks on a green side of Jaundice. I don't know what that is, but she looks way too green, and her lips are kind of greenish as well. Everything has got this gullish cast and we could back off if we wanted to in order to bring back her skin tones, and notice I am doing this by dragging this light gray region between the straight bar and the triangle. So I am dragging it over and that's condensing the area of absolute modification there, meaning that all of those colors are being completely adjusted.
In doing so, while that does bring back the skin tones and it leaves the shirt, it leaves the blouse yellow, but brings the skin tones back into the pink range with the exception of the lips, which remain a little too yellow here. The problem that we have, I am going to go ahead and zoom in on her blouse quite a bit here. This is a fairly high resolution image actually. You can see that we have this fringe of red that's tracing all the way around between her blouse and the background. It's tracing around the buttons as well, and that's no good. That's just a big give away that we have been inside this image, and we've modified it. So we need to somehow change those reds and really the only way to change those edges is to change more colors inside of the image. I basically have to take this thing way the heck over at this point.
So in fact, I am going to expand my range. I am going to go ahead and drag the Vertical Bar over to 355 degrees actually, 355 degrees you can track it right there. These basically, when you are dragging these little triangles and so forth around, it's like dragging the halves of the triangles that are associated with the Luminance sliders inside of the Blending Options panel of the Layer Style dialog box. Meaning that you don't really have numerical control, you can't dial in numbers. You just have to keep an eye on those numbers if you are interested in hitting specific values.
I am going to take this far right triangle over to 75 degrees, so you can see this guy switches over to 75 degrees. Notice now that we have a nice drop off, and that red edge is completely gone now. Okay. So that's good, because I would rather change too many colors and then use a layer mask in order to back it off. That's what I am going to have to do. In fact, just not really, like I have a choice at this point. Now, I am going to drag this Vertical Bar, the left hand of the two Vertical Bars here. I am going to drag it over to 325, just to make sure we are hitting everything we need to hit, and I am going to drag this far left triangle over to 295 like so. So 295 degrees/325 degrees, 355 degrees/75 degrees, that's what we are looking for along with Hue of 60, and Saturation of negative 10.
That means that we are covering all of our bases, but it also means that she is turning green and gullish. This is before this change, this is after. So we've got the blouse, we have done a beautiful job on the blouse. We have done a dreadful job to everything else inside the image. In fact, we have pretty much changed every single color inside this image that doesn't fall inside the jeans. The blue jeans are still blue jeans. They are still the same color they were before, but we have even changed much of the background here. You can see that we have these hot green dandelions going in the background.
But anyway, go ahead and click OK in order to accept that modification. It just goes a proof that we need a color mask inside of this image and we will be creating that color mask beginning in the next exercise.
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