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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 generate the Layer mask for highlights layer for this glass. So we are going to see one method for masking glass inside of Photoshop. Make sure that your highlights layer is selected and if you are just joining me incidentally, you can catch right up by opening this image. It's called Highlights & Shadows.psd. It is found inside the 11 Layer masks folder. Go ahead and click on the highlights layer which is currently set to the Screen mode. Now, we are going to be masking the glass using a combination of the Color Range command along with the Gradient tool.
If we were to select the Color Range command right now, so it would base its selection outline on that composite image as well. We don't want that to occur, we don't want these lines from the background layer to be taken into account. So we need to go ahead and switch the highlights layer to the Normal Blend mode by pressing Shift+Alt+N or Shift+Option+N on the Mac, and you can see that we now have the Normal Blend mode up here in the upper left- hand corner of the Layers palette. Also make sure that the Opacity and Fill values are set to a 100%, so that glass layer is fully opaque and the Color Range command will see the glass layer and only the glass layer.
Now, I want you to go up to the Select menu and choose the Color Range command or you can press that keyboard shortcut if you loaded my Deke shortcuts way back in the Preface, and you'll probably see an effect like this, where you see just a handful of pixels against the Black background, incidentally, if you are seeing a Grayscale version of the mask in the larger image window, then I want you to change your Selection Preview setting to None. As we need to be able to see the full RGB version of the image. I am going to go ahead and zoom in on the image by Ctrl+Spacebar clicking right here, that's Command+Spacebar clicking on the Mac. Notice this highlighted edge along the right side of the glass. These represent the hottest highlights inside of this image.
I want you to go ahead and click on that highlighted edge in order to lift those colors, as the base colors for the selection. And incidentally, if you want to make sure you are selecting exactly the right portion of the image, you can press the Caps Lock key, in order to get that precise cursor right there and then click in order to nail that area. And of course the Caps Lock key gets you any number of precise cursors when you are working inside a Photoshop. I am going to turn Caps Lock back off and I am going to go ahead and raise the Fuzziness value to a 140, which I would like you to do as well. And that's all I wanted to do, I don't wanted to lift any other base colors from the image, just that one white. Then raise the Fuzziness value to 140 luminous levels, and you'll end up generating a selection like this.
In order to confirm what it looks like, you can now change the Selection Preview to Grayscale, and you'll see that, that edge, that hot edge is absolutely selected. The bright colors in the upper right region of the image are mostly selected, they are pretty darn, almost entirely 100% selected. And then the Shadows of course are deselected, the Midtones are selected to a lesser extent and so on. Now that we have generated our base selection, go ahead and Click OK in order to display the marching ants inside of the Image window. I am going to zoom out here a little bit, back to the 50% View size, and when I am going to convert these marching ants to a layer mask by clicking on the Layer mask icon down here at the bottom of the Layers palette, and assuming that the highlights layer was active, you just went ahead and added a Layer mask to that highlights layer and you'll get an effect that look something like this on screen.
Now we still have these ultralight highlights appearing in the upper right region of the image, that's no good and we are going to get rid of them using the Gradient tool. So I want you to switch to the Gradient tool here inside of the toolbox. You can get that tool by pressing the G key if you like. Next I want you to switch from a Linear Gradient to a Radial Gradient, and you can do that by clicking on this Radial Gradient option in the Options bar. For those of you who just love keyboard shortcuts who just geek out on the stuff. I am going to tell you, a really great keyboard shortcut. You can switch the style of gradient by pressing the bracket keys. All right, so left bracket goes one way, right bracket goes the other way; just an FYI, just a little bit of sugar from me to you.
Next, we want to switch the kind of gradient that we are going to apply; the color of the gradient to Foreground to Transparent; this one right here. So go ahead and click on it and then press the Enter key or the Return key on the Mac in order to accept that setting. Make sure that black is your foreground color, if it isn't, press the D key and then the X key to make it so. Next, I want you to reduce the Opacity of this gradient to 70%, and finally, notice if we were to start dragging with this Gradient tool right now, we would draw a gradient that's black in the center and translucent on the outside. So we would create a hole in the center of the glass, that's no good.
We want our hole to be out here inside of the background. So I am going to go ahead and undo that modification and turn on the Reverse check box up here in the Options bar, so you draw a gradient from transparency to 70% black. Now, I am going to switch the Full Screen mode here by pressing the F key, and then I am going to drag my glass down a little bit so that I have plenty of head room up here. And I am going to draw from the center of the glass to about here inside of the pace board, do you see that line? And then I am going to release my mouse button in order to draw a gradient that looks like this.
And you can see now, if I would to Alt+ Click or Option+Click on the Layer mask thumbnail, here inside the Layers palette, this is what the Layer mask looks like after I add the gradient, this is what it looked like before. So I just ever so slightly darkened the upper right region of the image. Actually, I ever so slightly darkened all the way around in the concentric circle around the glass, and I darkened the highlights a little bit inside the glass as well, but I just tempered them slightly and I think it actually delivers a really nice result. So let's go ahead and Alt+Click or Option+Click on that Layer mask thumbnail again, to see the composite RGB version of the image. This is before the gradient and this is after the gradient, a very nice improvement and we are focusing just on the highlights inside of the glass, as well as those shadows, so it looks really nice.
The next thing I want to do is, I want to temper those highlights a little bit more, by moving the highlights layer below the glass shadows layer. So I am going to go ahead and drag it underneath like that. Then the highlights become too muted because the shadows are taking priority over the highlights. So I am going to switch to a different Blend mode. I'll press Shift+Alt+S or Shift+Option+S on the Mac and that didn't change anything. Why not? Because my Gradient tool is active. My Gradient tool went ahead and gobbled up the Screen mode. So I'll press Shift+Alt+N or Shift+Option+N on the Mac to switch the mode back to Normal.
Then I will switch the Rectangle Marquee tool and press Shift+Alt+S or Shift+Option+S to change the layer to the Screen mode, that's still not quite enough, so I'll press Shift+ to switch to the Color Dodge mode and then Shift+ to switch to the Linear Dodge mode, and that to me looks really great. So we have a combination of the Linear Dodge and Linear Burn modes working together here and the highlights are modified by a Layer mask, thus successfully masking the glass against its new background.
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