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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."
Here I am working inside of this merged 32-bit HDR photograph and I have managed to expose for both the land and the sky using this Levels adjustment layer right there. And I am working by the way, if you want to catch up with me; I now have a catchup document for you. It's called Exposed land & sky.psd, and notice that I have saved it in the PSD format as opposed to the radiance format, that HDR format, because my image contains layers. And by the way, I had to make sure it also contains an Alpha Channel. So I had to make sure when I was saving the image to turn on the Alpha Channels checkbox, because it wanted to turn it off and save the image as a copy. So make sure that all of your checkboxes are turned on. All the checkboxes that you can turn on, that is, are turned on if you were to save a layered HDR file.
Now, I am going to go ahead and click the Cancel button because I have already saved this image for you. You can see that we have a pretty bad mask going on here. Now there are all kinds of ways that we could fix this mask if are working in a 16-bit or 8-bit per channel mode. But because we are working with 32-bit, we lack some options. For one thing I should tell you, if you go to the blend mode pop-up menu, you will see here that we are lacking some critical blend modes including, by the way, Overlay, that's a big tragedy and here is the worst of it, Screen. We are missing the Screen blend mode because of the way that Photoshop calculates the highlights, the way that a previous highlights we don't have Screen available to us.
We also by the way, don't have the Invert command available to us either. So I can't really, for example, do like -- let's say I wanted to do a Motion Blur and then I would Screen that Motion Blur into place using the Fade command which we do have. It would be available if we had applied Motion Blur. But I wouldn't be able to Screen it into place in order to avoid the Motion Blur in both directions. So I might go ahead and invert the mask and then Motion Blur and Multiply it. But we don't have an Invert command. If I click on the layer mask icon here and go to the Image menu and choose Adjustments, no Invert. So that's a problem.
Basically, just about everything that's applicable to highlights, is missing. And not strictly speaking everything. We do have the Light mode and we do have the Linear Dodge Add mode. But we don't have Add and Subtract either. So we are limited in terms of what we can do. So we are going to do a little bit of fakery. Go ahead and make sure that the layer mask is active. I am going to Shift+Tab away the palettes and I am going to grab the Gradient tool right here. And I am going to switch to this Gradient, the Foreground to Transparent Gradient. Make sure that Linear is turned on.
Let's switch the foreground color to white and I am going to zoom out just a little bit so I can take in more of the image. And then, I am going to go ahead and drag down from the mountains, like so. It just may be a little bit of an angle. But notice that kind of overly darkens all of the hills. It does go ahead and take care of that rough transition. But it overly darkens the hills. And then I am going to come back with the Brush tool and I have got a big soft brush. Notice that I have 1100 pixel brush going right now. And I don't want to paint with white. I want to paint with black. So I will reverse my colors right there. And I will just sort of click around inside of the background here in order to lighten the scene. It's almost like I am dodging the scene really.
So I just have to kind of choose the areas where I want to bring back the old sky where I think it looks good. We get a nice blend of the old sky along with the new sky, that is the lighter sky merged along with the darker sky. And something along these lines here, I think looks pretty good. And actually, it looks better than if we had put together a mask that totally, accurately traced the outlines of the hills, because we need some sort of interaction between the sky and the hills that makes a little bit more sense. I am going to press the 5 key in order to reduce the Opacity value to 50%. I am going to click there in order to create a 50% merge of light sky with black sky and I will click here as well, and I get this effect. I think it looks actually pretty darn good. I might do a few more 50% clicks like that. That's a little bit too much actually. Let's take the Opacity down to 20% by pressing the 2 key and click again, and that looks pretty nice to me.
All right. So anyway, just click around, have fun. Basically we are just kind of doing a painterly mask at this point. Thanks to our limited options. But, you know what, the limited options ensure that we got a better looking effect in my opinion. In the next exercise, we are going to take this 32-bit per channel image and we are going to down sample it to a 16-bit per channel image so that we have basically an image that we can share with other folks. And now actually that way, we also have more options available to us in terms of modifying this image. By the way, look at that. This is way too dark over here. So I will go ahead and paint this away a few times in order to resolve that area.
All right, so anyway, join me in the next exercise for converting from 32-bit down to 16.
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