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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."
Now, the overarching theme of this chapter is channel mixing, ways to mix channels together inside Photoshop. Many times the reason that you are going to want to mix channels together is to convert a full color image into a custom black and white image. So before we start looking at those methods for creating custom black and whites, I want to show you the three basic ways to get gray inside of Photoshop. Now, I will be demonstrating these three ways to gray using this image right here that's called YSM.psd and I have resorted to acronyms for my file naming conventions inside of this chapter just to mix things up, just to keep things interesting. In this case, YSM stands for you are smooshing me. If we see the image from her perspective afterall she is being rather smooshed by this fellow. He is taking up more than his fair share of the image I think.
I think it's a beautiful image though. It comes to us from photographer Alexander Hafemann once again of istockphoto.com. So what are we going to do? Well, we are going to test out as I say the three ways to gray. So I am going to create a few duplicates of this image. I am going to go up to the Image menu and choose the Duplicate command and I am going to call this first one Method 1 and click OK, and then we'll make a duplicate of that image and call it Method 2 and then I will go ahead and duplicate that image by choosing the Duplicate command from the Image menu and I'll call it Method 3, all right and click OK.
So we have got base images for each of our three methods here. Let's go ahead and advance over to Method 1, and the first method for creating a grayscale image. Before I show you that by the way, I need to show you how this image is constructed. I am going to bring up the Layers palette and you can see that there is the smart object that's called Close couple. So I went ahead and converted the background image to a smart object and then I've applied the High Pass filter and if you double-click on the word High Pass there, you will see that I applied a radius of 12 pixels or a fairly high radius value, go ahead and cancel out. And of course I also, if I double-click on this little slider icon here, you'll see that I set the Mode to Overlay, so that the High Pass filter is mixing in properly with the underlying original otherwise it would look like this, it would look all gray and bad of course.
All right, so I will Cancel out of there. Now, because I am setting the High Pass filter to a fairly high radius value, we're not getting so much of a sharpening effect rather we're just getting a high contrast effect and enhanced contrast effect and so this is without the filter. This is with the filter. So very subtle effect, and you can see that I have got a density mask going right here in order to limit the effects of the High Pass layer to just the darkest regions inside of the image. Okay, so I point that out just because that will make a difference in terms of my conversions. That's going to inspire Photoshop to bring up a bunch of alert messages as we work through this image. So Method number 1, I will go ahead and Shift+Tab away the palettes. Method number 1 for creating the grayscale image, is to go up to the Image menu, choose Mode and choose Grayscale, that's it. I am kind of reviewing familiar territory. We saw some of these methods way back in Chapter 01 of course.
But I will go ahead and choose Grayscale. Photoshop will come up with one of two messages depending on whether I have got a layered document, it will ask me if I want to flatten the image or not flatten the image. In this case, because I have got a smart object going with the smart filter applied to it, it's asking me do I want to rasterize the image meaning, do I want to basically flatten the image once again, convert all of the smart filters to just a base image. Or do I not want to do that, do I want to not rasterize the image? What I recommend you do is when in doubt, click on the Don't button. Whatever it is, don't flatten or don't rasterize, click on that, or just press the D key for Don't either on the Mac or the PC. What that gives us by the way, I will go ahead and bring back my Layers palette, you can see that in addition to a grayscale image -- I will go to the Channels palette, you can see that it's a single channeled image. We've just got a single gray channel. This guy right here Close couple Filter Mask is of course a filter mask that's assigned to the Smart Filter.
I will return to Layers palette and you can see that I do indeed have my smart object intact along with my Smart Filter and my density mask and so on. So that's a good thing. It's better to keep that information as you can as I have and you do that of course by clicking on the Don't button or pressing the D key. All right, so that's Method number 1. Method number 2, rather than creating a composite grayscale image which is what we just got through doing, you can keep a single channel inside the image. So you could go over to the Channels palette. So notice that I have the Method number 2 image opened here. I will go to the Channels palette and I could click on the Red channel, click on the Green channel, click on the Blue channel, decide which channel it is that I want to keep. In my case, let's say, you know what, Green looks like the best grayscale version of the image.
Then, I would go up to the Image menu, choose Mode, choose Grayscale so the exact same command, but because I have a single channel selected, Photoshop is going to dispose of the other two channels. And in doing so, it's going to say hey, do you want to flatten the layers? Yes or no baby, those are your only options, don't give me a D for don't this time around. Just do it or don't do it. I am going to say OK because that's the only choice I have if I want to continue on here, and you can see that we end up with a single gray channel of course and if I go back to Layers palette, things are flattened.
All right, so moving right along, here is Method number 3. Now you'll hear people say, gosh, you don't want to work this way, you don't want to convert an RGB image to a grayscale image composite-wise and you don't want to convert a single channel like Red, Green or Blue. Instead, you want to keep the real luminance information baby and if you want to go that route, then you go up to the Image menu, you choose Mode and you choose Lab Color in order to convert the RGB image over to Lab which is Luminance plus the A and B channels. So I will go ahead and choose Lab Color.
Do you want to rasterize or don't rasterize? Of course it's Don't, press the D key for Don't Rasterize. The image looks the same. So it's a good convention and we've managed to keep the smart object and the Smart Filter intact. Go over to the Channels palette, you can see that we have Lightness as well as the a channel which is the Tint information and a b channel which is the Temperature information. Obviously a and b would make, I would say remarkably poor grayscale versions of this image. So let's go back to Lightness and I will go up to the Image menu and I'll choose Mode and I'll choose Grayscale, same old, same old. Again, Photoshop is with the, do you want or do you not want to do it, because you've got a single channel selected? I want to so I will click OK. I end up with the single gray channel, layers are flattened.
So those are the three variations on the image, so I am going to Shift+Tab away my palette. All right, let's review what we've done. I am going to switch over to the Method number 1 image. Method number 1 you will recall is the RGB to Grayscale Composite Conversion ends up with this version of the image here, compare that to keeping the Green channel only, it's a slightly lighter version of the image. The shadows are a lot more open meaning the shadow information is lighter. Then finally, we've got the conversion of the lightness channel only. That's the lightest version of the image because that lightness channel is really designed to include the color information building on top of it as well. So again, this is lightness and this is green and this is the composite conversion. You choose, anyone of them is completely acceptable of course.
Those are the base conversion options for going from color to grayscale inside of Photoshop. We'll look at ways to create custom color to black and white conversions starting in the next exercise.
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