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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."
All right, now throughout the remainder of this chapter we are going to be taking a look at the most practical application of HDR, 32-bit HDR inside Photoshop, and that's the Merge to HDR function which allows you to merge multiple exposures of a scene into a single 32 Bit/Channel image at which point you can modify the exposure of the photograph in order to get just absolutely the perfect shot, at least that's the idea. And what we are going to do I am going to set things up in this exercise, we are going to see why HDR is so useful.
Then in the next exercise we'll go ahead and apply the Merge to HDR command. But here is the deal, I should say this by way of background here. HDR is very commonly used in the world of 3D graphics. It's also pretty common for video work and especially for 3D film work. But it's only just now sort of catching on in the world of still photography. So you have to consider to be -- right now you have to consider to be bleeding edge technology. So in Photoshop defense this is all very, very new. In Photoshop CS2 it was the first version of Photoshop to support HDR. It's gotten better in Photoshop CS3 but it's still a far cry from being a polished feature. So there is a little bit of roughness, it's useful, but there is a little bit of roughness associated with it as you'll see. All right, so here is the idea.
I've got the Bridge; I am working on the Bridge right now and I have it trained on this 17_16bit_HDR folder. And I've got a series of three images called Lake Powell_1.dng, Lake Powell_2.dng, and Lake Powell_3.dng. And these are three Raw images that I shot using an SLR camera. And the idea is we were vacationing in Lake Powell, we had rendered a houseboat totally a wonderful trippy time, it was really great time. And we had just gone through docking the boat. I set the anchors by the way. Later one of the anchor would come loose and the boat would start to float away.
That was quite the adventure as well. But anyways, during the day or sort of the waning daylight, I sort of hiked up the side of the mountain here and I wanted to take in the houseboat along with the entire scene. And I am obviously losing the light, and I can't really capture the entire scene with any single combination of aperture and shutter speed and ISO. So this one right here Lake Powell_1.dng; you will see it's kind of the middle shots, it's probably the best over all exposure. But we are losing the sky. The sky is going to totally white over here, and we are starting to lose the houseboat as well. Not really the way we would later that night when the anchor came loose but we are starting to lose it in the shadows here.
So what I did was I set my camera to Auto-bracket, and the idea behind Auto-bracketing is you set your camera and this is very common with SLR cameras, you set your camera to take three shots in a row just bang, bang, bang. And automatically vary either the aperture or the shutter speed or both depending on your preferences, in order to take a perfectly exposed shot which would be this one by the way. And then to go one level down and then one level up from that shot.
Now I let everything ride here, I let everything vary. So I allowed my camera to ahead and vary both the shutter speed and the aperture. Technically you are supposed to just vary the shutter speed, but Merge to HDR does work if you allow the aperture to vary as well as we'll see. And you also notice that I am not working with the tripoded shot. So if I click on Lake Powell_1.dng again, and then Lake Powell_3.dng, there are the two that depart from each other. You can see that the scene is sort of listing a little bit, and that's because I don't have a tripod, I don't have a mono-pod, I don't have a nothing pod. I am just shooting the pictures, and even though the shutter is firing away bang, bang, I feel moved enough that there is movement in the shot and there is also movement in the water. And whatever the heck this thing is, is moving in the background.
Now, that would have completely confused Photoshop CS2. Photoshop CS3, thanks to its Auto-alignment function that we saw back when we were looking at tumult at the aviary is capable of dealing movement inside the shots. So it's great, in that regard it's really, really great. So what we are going to do is we are going to take these three images, and notice that the first one as I said the sky is blown the houseboat in darkness, the underexposed shot, the houseboat way in darkness but we have better sky detail. And actually I think we have all of that sky as it turns out. It's looking like it's a little bit clipped over here in the highlights. But it's a DNG file so it's Raw digital camera file. So there is highlight detail that we just can't quite see.
And then we've got the overexposed shot in which we are definitely losing the sky but we can see the boat. And so it's not really an overexposed shot. It's just that it's exposed for the boat and two it's exposed for the sky, and then one it's got exposed for everything in between. We are going to merge all three of them together to get the perfect 32-bit HDR shot starting in the next exercise.
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