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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, I am going to introduce you to the Channel Mixer command which allows us to mix color channels together in order to among other things, craft our own custom black and white image which is what we're about to do. I am looking at the image called YSM. psd. YSM of course stands for you are smooshing me because this guy right here is going hey, hello. How are you? I am star of the image and this poor woman is going help, you are smooshing me! Something along those lines.
At least, as I say, that's the story I am reading into the image. Your version may vary. In addition to the you are smooshing me image, I have got a couple of other variations here that I have created, that I created in the previous exercise that is to say, and you can go ahead and open them up as well if you want to. The first one is called Method 1(composite).psd so called because that was an RGB to Grayscale Composite Conversion and then we've got Method 2(green).jpg so called because I kept the Green channel, and threw away the Red and Blue channels. I could adjust this easily, kept the Red channel or kept the Blue channel if I wanted to.
Then finally, we've got Method 3 (lightness).jpg. I went ahead and converted the RGB image to Lab, then I selected the Lightness channel and converted it to grayscale, threw away a and b. So we have three different grayscale conversions going just for the sake of comparison. Each one of these by the way is found inside of the Ways to gray subfolder which is found inside of the 13 Channel mix folder. I am going to return to this guy right here the YSM.psd image and let's go ahead and apply the Channel Mixer function. Now, I could go up to the Image menu and choose Adjustments and then choose Channel Mixer if I wanted to apply a flat conversion. The Channel Mixer command in this case is dimmed because I can't affect the pixels directly inside of a smart object inside Photoshop. So instead, I am going to apply a more versatile adjustment layer.
So I am going to click on Close couple once again here inside the Layers palette. Then, I will press the Alt key or the Option key on the Mac, click-and-hold on the Black/White icon and choose Channel Mixer. Thanks to the fact that I have the Alt or Option key down, that bring up the New Layer dialog box. I will name this layer B&W and then I will click OK in order to bring up the Channel Mixer dialog box. Now, the first thing that the Channel Mixer dialog box allows us to do is to mix the Red, Green, and Blue channels into each of the Red, Green, and Blue channels, meaning for example, right now I am affecting the contents of the Red channel and I could change the Red channel to include so much Red like I could reduce the amount of Red, I could increase the amount of Green and I could increase the amount of Blue as well. So that I am adding green and blue to the Red channel.
Now, notice in this case, I have just applied some arbitrary values, but I am adding 57% Red to 71% Green and 27% Blue and I see that the Total is 155% altogether meaning that I am brightening the heck out of the Red channel. I am increasing it beyond 100%. I love this new addition inside of Photoshop CS3 the fact that it does the math for you, so that you don't have to track the math for yourself. In this case, this little warning is saying, hey, you are going too high. You might want to tone something down. So I would go ahead and reduce the amount of Red in this channel for example and notice as I do, it's tracking the total for me. It's telling me I am still too high. I will go ahead and take it down another ten down to 2% and as soon as I do, the little warning icon goes away.
It tells me that I am at 100%. I don't get a warning if I go too low. Notice that, if I go under 100%, there is no warning anymore which I think is kind of a strange decision on Adobe's part but that's the way it is. It still does track the total, that's nice. So that would give me sort of this goulish couple right there. If I were to modify their contents of the Red channel in such a way here, I can also change the Green and Blue channels if I want to. Now, if I am mixing my own custom black and white version of the image, then I want to turn on this checkbox right here Monochrome. So that I am mixing Red, Green, and Blue into a new gray version of the image as it were. So I will turn on the Monochrome checkbox, notice my Output Channel is now Gray. I can see that I am getting a grayscale version of the image.
By default, Photoshop wants to give you 40% Red mix with 40% Green and 20% Blue. Notice that, that adds up to 100%, if I were to change the values, I would get a new total as well. But for now, I am just going to accept these default values here and I am gong to click OK. So it's mostly Red and Green, equal parts Red and Green with half as much Blue added in. Then, I will go ahead and click OK to accept that modification there and let's go ahead and Shift+Tab away the palette so that we can see the entire custom grayscale version of the image. This is the Channel Mixer version of the image compared with the Composite Grayscale Conversion. It looks very similar. This is Method 1(composite).psd, so I just switch to this image.
So this is, once again just for the sake of comparison, this is the Channel Mixer version. Take a close look, and now I am going to switch this is the composite version. You'll see very, very little difference, just a slight little switch on screen. But they are not identical, so there are some differences. For example, if we switch back to the YSM image which is the Channel Mixer version of the image, you can see that the background is darker. Check out the background, slightly darker, it lightens up when we switch to the Composite RGB to Grayscale Conversion. So it's a slightly different mix of the channels and when you go from RGB to Grayscale, you do indeed mix the channels according to a predefined equation. Doesn't happen to be the equation we just applied but it is a predefined equation.
Now, let me show you, let's go back to the YSM.psd image right here. I am going to Shift+Tab up my Layers palette, so I can see it once again. I am going to double-click on the adjustment layer, so that I can revisit the Channel Mixer dialog box, there is my default settings. Here is the actual equation that most applications use to convert from RGB to Grayscale, not exactly this equation because actually Photoshop makes us in a little bit of color management as well, so it alters the equation according to your color settings inside the program.
But this is basically, this is a base equation. It's 40% Red plus 50% Green, so I have raised that value to 50% and then I will Tab to Blue and I will press Shift+Down Arrow to lower that to 10%. So 40% plus 50% plus 10%, why is it a lot Red even more Green and barely any Blue, because of the way that our eyes react to light. We have more red and green cones in our eyes than we have blue cones. So we're not seeing much in the way of blue light when we're looking at the world and of course the RGB to Grayscale Conversion takes advantage of that.
This is also why the Green channel bears the closest resemblance to a Composite Grayscale Conversion because the Composite Grayscale Conversion is mostly green. So it's 40%, 50%, and 10%, that's your base conversion. This isn't Photoshop by the way, this is the world in general. This equation actually hails from the days of black and white television and so on. I will go ahead and click OK in order to apply that conversion, let's Shift+Tab away the palettes now, let's compare this to the Composite Grayscale version.
This is the YSM image obviously subject to the Channel Mixer adjustment layer and this is the Method 1(composite) image which we created by converting the RGB image to Grayscale, using Photoshop's default settings. You can see that they are very similar to each other. This is one and this is the other, and the slight, slight, slight changes you are seeing are mostly the result of the way that Photoshop is calculating the High Pass smart filter on the fly here at the 50% View mode.
So that gives you a sense not only of how the Channel Mixer function works, but also of how industry standard RGB to Grayscale conversion works. In the next exercise, I will show you some more thrilling ways and some more custom ways of course to use the Channel Mixer command.
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