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In the all-new Photoshop CS5 One-on-One: Mastery, the third and final installment of the popular series, join industry expert and award-winning author Deke McClelland for an in-depth tour of the most powerful and empowering features of Photoshop CS5. Discover the vast possibilities of traditional tools, such as masking and blend modes, and then delve into Smart Objects, Photomerge, as well as the new Puppet Warp, Mixer Brush, and HDR features. Exercise files accompany the course.
Recommended prerequisites: Photoshop CS5 One-on-One: Fundamentals and Photoshop CS5 One-on-One: Advanced.
In this exercise, I am going to demonstrate the two Inversion modes; Difference and Exclusion. I'll also show you the two new modes inside of Photoshop, Subtract and Divide, which I am calling for lack of a better term, the Cancellation modes. We will also see how they're not necessarily all that new. They are, in fact, variations on blend modes that we already had. So, I'm working inside Bright shining light.psd and I want you to get a careful look at this image here, just remember it, because we'll be coming back to it in an unexpected way in just a few moments.
But I have the wrestlers layer active and it's set to the Linear Burn mode. I am going to go ahead and change that mode to Difference. Difference produces as kind of psychedelic effect, it's actually extremely useful and I'm going to be showing you a practical application of it. But first, I want you to understand how it works. It's like the Subtract mode, in that it subtracts a pixel in the Active layer from an equivalent pixel in the composite view below. So that equation is basically B-A, just as it is with the Subtract mode. The difference is that you're taking the absolute value that is the subtraction never produces a negative number.
If it does, it just passed back up and becomes positive again. So difference will start by reducing the luminance of the image and then it will pop back up and increase the luminance once again. So you get these trippy inversion effects. The great thing is that it's a selective inversion. So Black doesn't invert at all which is why the black of the clothing is not performing an inversion. If I turn off the wrestlers layer, this is what the background parchment looks like. So it's bright, it's orange. When we turn on wrestlers, it remains bright and orange inside of their clothing and then it inverts in the white background.
So white inverts absolutely; all the other luminance levels invert based on their brightness on a channel-by-channel basis. So if you want to produce more normalized effect, you'd go ahead and invert the layer itself and you can do that if you're working along with me just by turning on this Invert Adjustment layer. Because it's clipped to the wrestlers layer, the default behavior inside of Photoshop is that the inversion happens first and then the blend mode is assigned. So when I turn this layer on, we can't see the effect applied to the thumbnail. But what we now have is white clothing and a black background, so the background is no longer inverting the parchment below it, but the clothing is, because it actually appears white to the blend mode.
All right, so as I say very useful mode for figuring out the differences between images, I will show you what that means coming right up. Now one more thing you should know is that similar colors cancel each other out. So if the Difference mode finds a blue pixel on the active layer and a blue pixel on the layers below, then it goes ahead and produces black. If you would rather produce gray instead, then you can switch to the next mode. That's the only real difference between these two, is exclusion is going to produce gray instead of black where similar colors are encountered. Otherwise, pretty much everything I told you applies; the luminance levels are inverting each other on a channel-by-channel basis.
If you want to see what this looks like without the invert layer then just go ahead and turn it off and we end up getting this effect here, and again, this is the Difference mode right there. A darker mode has punchier shadows and this is the exclusion mode which has a lighter touch to it. All right, here is the Subtract mode right there and Subtract goes ahead and does the same thing as Difference, except without the absolute value. So black isn't going to do anything because subtracting 0 results in the same color you have before. White is going to do a real number on the luminance because when you subtract white, since it's the biggest color there, you are going to wipe out any of your other luminance levels and that's certainly what's happening in the background here.
So just by way of a comparison, if I press Shift+Alt+E or Shift+Option+E on the Mac, that takes us to the Difference mode and what we're really seeing a difference between Difference and Subtract is in that dark background that brightens up considerably. All right, I am going to press Ctrl+Z or Command+Z on the Mac to return to the Subtract mode because it does not have a keyboard shortcut. I am going to turn on this invert layer so we can see what happens, when we subtract an inverted version of the image and we end up getting this amazingly familiar effect right here. In fact, now, I just want you to notice, this wrestlers is set to Subtract, so we can see this Subtract mode and the invert layer is turned on.
I am going to go up to the File menu and choose the Revert command to revert back to the Linear Burn version of the image and it's exactly the same. We did not see a single pixel change there inside the image window and yet, the wrestlers layer is now set to Linear Burn and the invert layer is turned off. Well, to confirm that's what really happened that we aren't seeing any difference, let's check out the math because whatever you think of the math, it never lies. I am going to go ahead and twirl up the text elements layer and turn on the blend math layer, scroll down a little bit, and notice, Linear Burn right there, is A+B-1.
That doesn't sound much like B-A, which is this subtract equation, but watch this. I'll go ahead and get my Type tool and edit this layer for you. I am going to enter an equal sign because ultimately, the two will be equal, and I am going to say B-A because that's the equation for subtract. But when you invert the A layer, it turns into this, in parentheses 1-A and end parentheses like that ((1-A)). So it's B minus the product 1 minus A (B-(1-A)) and if you go ahead and spin that math out, why then you get minus minus for A, those two cancel each other out so you get a positive A. The B was already positive so it's A+B and then minus is assigned to the 1 gives us a -1.
So they are in fact exactly the same operations. Subtracting an inverted layer produces the exact same effect as not inverting the layer and assigning the Linear Burn mode. We also have something that's resembling a Divide mode right over here in the case of Color Dodge. Notice we have B/(1-A). Well, the equation for the Divide mode which we we're about to see is just B/A. So, if we invert that A, we are going to get the same effect as Color Dodge.
Let's go ahead and prove that to be true here. I am going to twirl close the text elements group just so that I can get to some of my other layers here. Now I'll go ahead and set up the scene a little bit. I'll twirl open future stuff and I'll turn on bright to dark, so that we're darkening up the background layer and then I'll twirl that closed once again. Let's select the wrestlers layer and I am going to go ahead and change that blend mode to Color Dodge right there because this is the one that's B/(1-A), and we get this effect and I like it better if it's inverted. So we'll go ahead and turn on Inversion for this effect, like so, and I will save off this effect as a layer Comp.
I will go ahead and click on the Page icon and I'll call this Inverted Color Dodge like so, just so we can keep track of it. Actually Inverted, pardon me; I'll go ahead and enter an ed. Make sure Appearance is turned on that's important. So we save those Blend modes. Click OK. All right, now I am going to change the Blend mode for wrestlers from Color Dodge all the way down here to Divide. Then I am going to turn the Inversion off and we have that exact same effect. Just to confirm that it is exactly the effect we had ten seconds ago, I will click in front of Inverted Color Dodge and notice nothing changed onscreen whatsoever.
So I was working free and easily with the inversion; I ended up inverting both the layers as I was applying the operation, but that's a pretty easy thing to do that's something you can do to change the balance of power where these various blended layers are concerned. All right, so that gives you a sense of what to expect from these Blend modes. In the next exercise, I am going to show you a very practical application of Difference.
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