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Photoshop CS5 One-on-One: Advanced, the second part of the popular and comprehensive series, updated for CS5, follows internationally renowned Photoshop guru Deke McClelland as he dives into the workings of Photoshop. He explores such digital-age wonders as the Levels and Curves commands, edge-detection filters, advanced compositing techniques, vector-based text, the Liquify filter, and Camera Raw. Deke also teaches tried-and-true methods for sharpening details, smoothing over wrinkles and imperfections, and enhancing colors without harming the original image. Exercise files accompany the course.
Recommended prerequisite: Photoshop CS5 One-on-One: Fundamentals.
In this exercise we are going to see how to mix a custom black-and-white blend using the Channel Mixer. I've got two versions of that Scott Griessel image open here; the original full-color Agrarian gothic.jpg file, and I also have open Grayscale composite.jpg. You may recall, this is a very first grayscale version of the file I created just by taking the full color composite RGB image, then I went up to the Image menu, I chose mode, and I chose Grayscale. So in other words it's Photoshop's default blend of the Red, Green, and Blue Channels and Photoshop follows the same recipe every time you choose that command when you're blending down the entire image.
You can actually mimic that recipe using the Channel Mixer. So let me show you that here. I am going to switch back to the full-color image, switch over to Layers panel, and I'll will bring up the Adjustments panel, and I'll Alt+Click or Option+Click on that final icon in the second row which is the Channel Mixer icon. Let's go ahead and call this Custom B&W, and then I'll click OK. We've seen how you can select the output channel; that is you can modify the contents of the Red Channel or the Green Channel or the Blue Channel. However, when you select this Monochrome check box, then you're blending down just a single channel of information, and it's gray.
Now that doesn't mean you're actually converting to the Grayscale mode because you're applying an Adjustment layer. It does mean that even though you're still working in the RGB mode, each one of your channels Red, Green, and Blue at least the composite view of that channel is identical so that you're mixing what is ultimately a grayscale image. The only reason by the way when you go from Red to RGB, the reason it darkens down when you go from the Single Channel view to the Composite View is because when you're looking at a Single Channel, Photoshop is not color managing that transition, but as soon as you look at the full RGB image, it is color managing the image.
So that's what's going on there. Anyway, I am going to switch back to the Layers panel. We do still have a Red, Green, Blue image in our possession, so this is just a temporary modification by virtue of the fact we're applying an Adjustment layer. Notice this is the default recipe right here; Red 40%, Green 40%, Blue 20%. At least that's the recipe that the Channel Mixer automatically suggests when you turn on Monochrome. It is very similar by the way to the Grayscale Composite image. Notice this, if I go ahead switch to Grayscale Composite, things brighten up ever so slightly but we're getting something very nearly resembling the same effect.
Well, it's actually little bit different than this though; I am going to switch back to the RGB image and of course the Channel Mixer Adjustment layer, and I'm going to take this Green value, and I am going to raise it to +50, and I am going to take the Blue value and lower it to +10; so 40% Red; even more Green, very little Blue. Notice now if I switch to that Grayscale composite, the image barely shifts at all. So that is much closer to the actual recipe that Photoshop uses, and Photoshop uses a fixed recipe every time.
The reason that this recipe happens to be very close to what Photoshop uses is because it's something of an industry standard. This was actually the formula that was first employed by black-and-white television sets when they were interpreting full-color signals. It's a very common mix of the Color channels, and you should just bear it in mind when you're mixing your own black-and-white images that this is the default. So if you want to go your own way, you should probably vary from those settings. By the way, also notice that the total is adding up to 100% and you want to keep it at 100% unless you're keeping a close eye on your histogram, and you know for some reason that you have some wiggle room in the highlights, or the shadows or you have some specific reason for clipping those highlights and shadows, in which case you can go ahead and vary from that total.
Also, you've got this Constant option. Now, I don't think much of this Constant option, I'll show you why? If I raise it to 10%, I just scoot that entire histogram over 10%. So I completely lose my shadows. I end up clipping the heck out of my highlights. Where did this 10% come from? Nowhere. I just added 10% brightness to the entire image overall. It's analogous to the awful horrible behavior of the Brightness/Contrast command back in the old days. So I suppose, and I am being very generous here, I suppose there might be times where you could use this Constant value in very small increments like 1%, 2% that kind of thing, but like I said, I'm being very generous; anyway, let me show you why it is that Red and Green are emphasized so much more than Blue.
Let's go ahead and turn off this Adjustment layer for a moment, and hide the Adjustments panel, and then I will go back to the full-color image. Let's go over to the Channels panel a moment, and let's take a look at the independent channels. This is the Red Channel. So obviously, because we all as human beings resonate so brightly in that Red Channel, that is going to be a channel of emphasis when you go to mix down your final grayscale version of the image; that just stands to reason. That goes for when we are using the Black and White command too, which I'll show you shortly, you can up the amount of Red and Yellow that you include along within the image, and that just makes sense because that's going to elevate the skin tones.
Green meanwhile tends to be your Detail channel, and here's the reason why? Green is a channel of emphasis across all sorts of image capture devices. For example, consider your standard everyday average digital camera. It has the capture color in some way shape or form but it only has a single image sensor. So the light hits the image sensor and somehow not only does that image sensor have to be able to sense the brightness of the light that's hitting it, but it also has the sense of the color. Well, it can't really do the latter. It can't capture that color not in just one single pass.
So what it does instead, is it filters that light and so if you were to look at an image sensor, it actually contains as many pixels, just tiny little microscopic pixels of course, but it contains an image sensing pixel for every pixel inside your image; so any 2x2 block of pixel, so 2pixels wide and 2 pixels tall. It's got to basically filter this three colors of information; Red, Green, and Blue, so we've got 4 pixels, and we've got 3 colors. So what the Digital cameras typically do, and this is called a Bayer pattern by the way.
So what the image sensors typically do is they go ahead, and provide in any 2x2 block, there is one Red filter, there is one Blue filter, and then there is two Green filters. So in other words, across the entire image you have twice as much Green information as you do Red or Blue information. So as a result, Green is the channel that has the best luminance information inside it, where digital photographs are concerned, this also goes for a wider range of scanning devices as well. All right! So finally, Blue tends to be sort of the gunk channel.
It's where we as human beings respond the least, we're not resonating in this channel nearly as much, we are actually fairly complementary creatures where this channel is concerned. It's also where all of our blemishes are hanging out, as you can see here by; the location of all the freckles in her skin, not that freckles equate to blemishes, but you get the idea if we did have some blemishes going on, this is where they would be; skin modeling as well occurs here and so on. However, that's not always the case, and so I'm just telling you this is generally the way it is; Green has got the detail, Red has got our skin tones, Blue has got the junk.
But what you want to do is take a close look at your channels, and decide if that's really the way it is, because in our case, Blue is a fairly interesting channel. I mean, I actually like what's going on inside of her face inside this channel. All these freckles actually look really great and add drama it seems to me to the scene. Also, if you check out this woman who is out of focus in the background here, let's go ahead and zoom-in a little bit, actually quite a bit I guess. You'll notice that she has a fair amount, I'll go ahead and switch to the Red channel here, she has got an awful lot of posterizing, and stair-stepping, and stuff like that going on inside this Red channel.
So notice this very definite line, I'll switch to my Lasso tool; this very definite line that's going on right here along this bottom edge of her jaw, even though she is very much out of the focus in the background. So this is ultimately an artifact of the image. We have a fair amount of banding around her eye as well. Things stay pretty similar around the eye, in fact, you might argue they get a little worse in the Green channel but they get much better around the jaw line here in the Green channel. Then finally in the Blue channel, we actually have a fair amount of contouring going on both around the eyes and along the jaw line.
The only area that has sort of signs of posterizing is this area of intense shading right here. So we might even want to emphasize the Blue channel over the Green, and Red channels. In fact, what I would suggest where this particular image is concerned is that we go ahead and place primary emphasis on Blue, secondary emphasis on Green, and then the least amount of emphasis on Red, and I am going to show you how to do exactly that in the next exercise.
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