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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 correct the shot so that we have a nicely lit sky so that we are exposing the sky in a way that we want to, nice and dark actually, and then we elevate the exposure of the rest of the scenes so that the boat isn't mired in darkness down here, because after all, we have some pretty sky detail at this point. Then the rocks go very, very dark as you can see. And then this half of the scene, the right half of the scene is just mired and pitch black really. So the sun has left this region and the boat is in weird shape as well because we have these eerie blue shadows going on that don't fit the scene at all.
Now, I should mention that generally speaking, Photoshop has done a brilliant job of aligning this shot. All of the elements are aligned very nicely. The shot is kind of sagging over here on the right side of the image. So it's listing a little bit clockwise. And that's something that we will fix later. Also notice, if you zoom in here, I was telling you that there is a ski-doo or a jet ski in the background and that jet ski was moving of course. So the one motion trail that's associated with the jet ski ends up turning into three different motion trails right here. Actually I have to say, given that the water looks pretty darn good, it's pretty uniform, that this is really nice, that Auto Align feature. It's just a rocking feature inside Photoshop CS3.
But the exposure, I don't like it. We need to increase the exposure of the lower portion of the scene, and we are going to do that using a mask. And so what I want to do is, I want to select the sky. So let's go over to the Channels palette. Let's collapse the Navigator palette and check out. There is the Red channel. All right. So actually, why don't we go ahead and Shift+Tab away the palette so that we can see the entire scene. This is the Red channel right here. So pretty dark sky, dark everything really. And this is the Green channel. Things lighten up a little bit in the water and they lighten up in the sky as well. And then in the Blue channel, things lighten up even more. In the water, they darken in the earth tones of course.
And then the sky goes lighter still. Now what's tempting is say, OK, let's go ahead and expose this sky. Take the sky all the way white, right, because we want to select it and then, let's go ahead and duplicate that channel. Let's dup it by dragging it on to the Page icon at the bottom of the Channels palette, and it appears like that original. It's not a brilliant sky anymore. And in fact, that's because the thumbnails of course, have not been updated. But even if you went over to the View command and chose the 32-bit Preview options and change that in order to update the thumbnails, the Alpha Channel is still going to work from some other version, some original version, whatever Photoshop's concept of the original version of that Blue channel is.
So you can't edit it in other words, using this exposure value. So let's just go ahead and reset that back to something more reasonable, like for example, let's go to the RGB image and expose for that. I am going to go ahead and take this slider down just a little bit, right to there. And there is no values. Notice, the slider just kind of moves back and forth and you would just eyeball it. All right. Let's go over to the Blue copy item and let's call it Sky mask. And what we are going to do, is we are going to expose this sky mask. We are going to increase the brightness of the sky using the Levels command. So press Ctrl+L or Command+L on the Mac. Now I find that this Histogram inside the Levels dialog box verges on utterly and completely useless.
So I am just going to drag this guy over. Notice how far I have to go over in order to get rid of the sky. I am dragging this white point to 52. and of course, it's still talking to me in 8-bit language. This is 52 out of 256 different luminance levels you can have. Really, you have several octillion colors to choose from. But this is 52 which is not really true. So everything becomes fairly meaningless inside Levels. Again, you just need to eyeball things out here. But looks good right. The sky has definitely gone bright white and I am guessing, this stuff from here on, is representing sky detail and other bright details inside of the image.
So I will stay on this side of that cliff and I might go ahead and darken up the rest of the scene like this in order to make it go away by dragging the black point up and let's see, do we still have, we still have some little items here and there that we need to deal with. So I will go ahead and take the white point down further and the black point looks actually pretty good where it is. So I have got 51 and 54, there it is. And I will go ahead and click OK in order to accept that modification and we just created the mask from the image.
Now, it's a little bit of as hard edge mask. It's not jagged. But it is definitely a hard mask, I should say. And then if you find that you want to make some more changes like this here, it kind of needs to go away. You can go ahead and select it and press Alt+Backspace in our case because black is foreground color. So you can do some manual modifications. You also have a few filters that work for you here inside of the HDR mode, inside of 32-bit per channel, some blur functions that are available to you, the Add Noise command, Render whatever we got. We got clouds, who cares? We got a few sharpen functions, a Smart Sharp and an Unsharp Mask. We have got Emboss I bet, yup, sure enough. And then of course we have High Pass and Maximum and Minimum.
So your classic filters are basically available to us, especially the filters that are of the most use for the building masks. And so we could go in there with Blur and apply a little bit of Gaussian Blur. But I don't think we should. I think we should just leave it the way it is right now. All right. So we have a sky mask. We have managed to create a sky mask. And the beautiful thing about this is unlike previous projects, where I have showed you how to use a mask to select the sky and grab a sky from a different image and then paste that sky into a layer mask, we have got everything we need in this one image. We can expose for the boat area and we can expose for the sky, all in one image. It's just that it helps to have a sky mask to distinguish between those two zones.
All right. So we have done it. We created the sky mask inside of this image, inside of a 32-bit per channel image. Amazing, that we still have Alpha Channel control inside of 32-bit. I love that. In the next exercise, we are going to employ this sky mask in order to more properly expose the scene.
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