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Photoshop is one of the world’s most powerful image editors, and it can be daunting to try to use skillfully. Photoshop CS4 One-on-One: Advanced, the second part of the popular and comprehensive series, 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 CS4 One-on-One: Fundamentals.
Download Deke's customized keyboard layouts and color settings for Photoshop from the Exercise Files tab.
In this exercise, I'm going to show you the next pair of blend modes in the list here. These are the comparative modes, also known as the inversion modes, Difference and Exclusion, just a couple of them, pretty wacky modes as you will see in just a moment. I have gone ahead and saved my changes thus far as Texture mapping.psd. I have also gone ahead and saved out another comp. So if you go to Layer Comps palette, you will see this new one called Texture to LinLight because the Texture layer has been changed to Linear Light, and we can still switch back and forth between our various layer comps, don't you know? So let's go back to the statue layer for just a moment, and I'm going to turn off the Texture layer just so we can see the statue layer and how it interacts with it's groovy friends there in the background. And I'm going to press Shift+0 to raise the Fill Value to 100% and then I'm going to switch the blend mode all the way down here to Difference. And the Difference will be as you can see here.
And basically, what's going on is, mathematically, this is a subtract mode. So the luminance of the Statue layer is being subtracted from the luminance of the layers below. And then however, the mode is finding the absolute value, which means nothing ever goes negative. If it does go negative like, let's say you take 10-20, and that gives you -10. What an absolute value does is if it sees a negative sign, it lops it up and it makes it +10. So 20-10 and 10-20 deliver the same result. It's basically what it comes down to.
That means that the colors have a tendency to invert. So white inverts absolutely, black just becomes transparent, it doesn't do anything. And then, anytime two colors come in contact with each other, so a color in the Statue layer for example, more or less matches the color of a pixel below it, then we get black. And as a result, we tend to get these sort of psychedelic effects. Now I'll show you one way. It's a pretty useful blend mode. It's useful for finding differences between two things that look the same, so if you are trying to gauge something that's at work inside of Photoshop, you may find it to be a helpful blend mode.
All right, but first, let me compare Difference to Exclusion. I'm just going to go ahead and press Shift+Plus in order to advance to the Exclusion mode right there. The math that's in work for Exclusion is totally different than it is for Difference. So the two are completely unrelated. As a matter of fact, Exclusion is closest mathematically to Screen, and I got to Screen by pressing Shift+Alt+S or Shift+Option+S on the Mac. If I press Ctrl+Z or Command+Z to return to the Exclusion mode and then Ctrl+Z or Command+Z again to show off the Screen mode, you can see that the dark area is pretty much staying exactly the same, which is to say pretty well transparent.
And it's just the light areas that end up changing quite dramatically on this. Now what's happening with Exclusion, and this is roughly what's happening is that white is going to absolutely invert, and that would mean that we should get inversion out of the Outer Glow effect expect that as you may recall, outer effects. Effects that go outside of the layer by default do not get affected by the blend modes. So anyway, if we had any white, that would absolutely invert, any place that we have black just drops out as with Difference, but then where we start to see similar colors inside of the image that's when we start to get grayer effects as opposed to black.
With Difference we end up getting various shades of gray and it's going to work out differently in different channels. So in this case if I go to the red channel by pressing Ctrl+3 or Command+3, we can see that we have got some dark colors going on there. Ctrl+4 or Command+4 for the green channel, we have got grays. Ctrl+5 or Command+5 for the blue channel, we have grays as well. So because we had dark areas there inside the red channel, when I go back to the composite image by pressing Ctrl+ 2 or Command+2, we end up getting this sort of blue, greens right here inside of the statue's face. So let's switch things back to Difference by pressing Shift+Minus and I also want to show you how Difference is one of the Fill Opacity Eight.
So if I were to change the Opacity value to 70% by pressing the 7 key, we'd get this effect here, this water down version of what we saw before, whereas I'll press 0 for 100% Opacity and Shift+7 for 70% Fill Opacity, we get this effect right here. And it's not nearly as water down, and we have bolder colors, different colors anyway. We don't have those weird greens, we have got these lustrous purples instead, and just to give you a sense of the difference, this was the Opacity value of 70%, and this is the Fill Opacity value of 70%.
Notice we have got some nice dark black still here, still evident, when we reduce our Fill value whereas we don't have very much in the way of shadows. We have gone to the dark end to the midtones now, when we reduce the Opacity value to 70%. So let's leave things here at a Fill Opacity of 70% and Difference for the present. Now I want to show you something resembling a practical application of Difference, and we are going to do it using this image right here, Three Giulianos.psd, and we are going to take a look at this image. It's found inside the 17_blend_modes folder, but we are going to be taking a look at it in the very next exercise.
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