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Our next topic are the comparative modes, and those include just two modes inside the Blend Mode pop-up menu, Difference and Exclusion, both of which use a layer in order to invert the colors in the layers below them. Let me show you what I'm talking about here. I'm going to switch to the Statue layer inside my ongoing Sky & statue.psd composition. This layer currently has a Linear Burn mode applied to it. I'm going to switch from Linear Burn to Difference, and we get an inverted version of the face. But it's a controllable inversion, it's not strictly the kind of inversion you would get by choosing Image, Adjustments, Invert, for example.
It's much more selective, and it's organic to the image. So you're actually merging the Statue layer and blending it with the layers below. So here's what's going on. Any place where the layer is white, anywhere where the Statue layer is white, completely inverts the layers in back of it. Anywhere where the Statue layer is black, in the shadows here, you don't get any inversion whatsoever. And where like colors run into each other, they cancel each other out, and the image turns black. So as a result we get this sort of eerie luminescent glow to this image, a sort of underglow to it.
The Difference mode is another one of those modes that responds differently to Fill and Opacity, to the Fill and Opacity values here inside the Layers palette. So I'm going to go ahead and raise the Fill value to 100% by pressing Shift+0. And just for the sake of demonstration here, I'll take the Opacity value down to 70% by pressing the 7 key, so we just get a weaker version of the Difference image. Now I'll take it back to 100% by pressing Ctrl+Z or Cmd+Z on the Mac, and compare that to pressing Shift+7 to change the Fill Opacity to 70%. So instead of having the interior of the image turn a sort of weird green color, we end up getting a robust purple this time, sort of this organic violet, as it turns out, which I think is really nice.
So just remember, Difference is another one of these that responds differently to Opacity and Fill. Now it has a variation called Exclusion that does not respond differently to Opacity and Fill as it turns out. It behaves, I think, in a lesser fashion. Exclusion is one of the blend modes I really don't have a lot of use for. But I'll tell you how it works. White goes ahead and inverts, just like before. Black is not inverted all. Similar colors, that is similar colors in the Statue that match more or less the colors in the Gradient and Background layers, don't so much cancel each other out as turn gray. So you'll have a lot more colors turning gray inside of the image.
Not really what I'm going for in this case, so I'll go ahead and undo that modification so I can return to the Difference mode. And I'm going to leave this image set like this, Difference mode and Fill Opacity of 70% for the moment, applied to the Statue layer, we're sort of playing around here. Now, you might think, okay well there's another mode to add to your list of blend modes, but why in the world would you ever really use Difference other than to achieve some sort of weird psychedelic inversion effect? Well, let me show you. The Difference mode can be very useful for finding differences between images. I'm going to go ahead and press Ctrl+Tab here in order to switch to another image that I have open. It's called Three Giulianos.psd, and it is indeed three copies of the Michelangelo sculpture of Giuliano de Medici.
And this image can be found by the way inside the 15 Blend Modes folder. Now, you should see giuliano 2 selected inside the Layers palette. Giuliano 1 for the moment should be turned off. I want you to go up to the Filter menu, and I want you to choose the Noise command, and I want you to choose Median. What we're going to do is just run a comparison between the Median filter and the Gaussian Blur filter. So let's go ahead and set the Median filter to a Radius of 10 pixels and then click OK. Sure enough, we get sort of this rounded edges effect, just as we might expect from having learned how the Median filter works.
Alright, now I'm going to click on the giuliano 1 layer and turn it on, and let's go ahead and apply the Gaussian Blur filter to this image. I'll go to the Blur menu under the Filter menu, and then I'll choose Gaussian Blur, and I will enter once again a Radius value of 10 pixels and I'll click OK. So we now have a blurred version of Giuliano on one layer and a Median version of Giuliano on another layer. Let's go ahead and compare those two layers by going up to the Blend Mode pop-up menu and choosing the Difference command, which allows us to figure out exactly where the differences are. So anywhere where we see black, there are no differences. The two layers are identical to each other. Anywhere where we see any other colors going on, those represent the differences between the two layers. Now our differences are looking pretty murky at this point.
Let's boost the contrast by merging the two layers together and then applying the Levels command. So I want you to go to the Layer menu, with giuliano 1 selected, by the way, and choose the Merge Down command, or you can press Ctrl+E if you like, Cmnd+E on the Mac, to merge those two layers together. So now we have a single layer called giulano 2 that is the Difference blend of the Median and Gaussian Blur effects. Now I'm going to press Ctrl+L in order to bring up the Levels command. That's of course Cmd+L on the Mac, and I'm going to drag this white slider triangle over to the side of the histogram, until I get a final Input Levels value of 50. So I'm saying anything with the brightness value of 50 or lighter, make white. So we're creating a lot of highlights inside of this Difference image. We'll go ahead and click OK, and now you can really see where the differences are occurring. I'll go ahead and zoom in to this hair and ear region right here. The sort of striation patterns, these little sort of cross-hatched rectangle patterns going on, those are a function of the Median filter.
And then the soft glows that you can see around the eyes and so forth, that's a function of the Gaussian Blur filter. Now I'm going to take this giuliano 2 image that I've sort of created as a combination of Median and Gaussian Blur and of course the Difference blend mode, and I'm going to blend it with the giuliano 3 image in back, which is just the original image. If you turn off giuliano 2, you'll see that giuliano 3 is an unmodified version of the statue. Alright so I'll turn giuliano 2 on once again, and I'm going to switch this to the Color Dodge mode, so we keep just the highlights, and we're going to have some nice, bright, vivid highlights associated with this image. I'll press the Escape key to deactivate the Blend Mode pop-up menu. I'm going to zoom in actually another click, so that we can see the image at 100% view size, and I'm now going to press Shift+5 in order to reduce the Fill Opacity value to 50%.
So we just get these nice highlights, some nice, eye-popping highlights here around the edges of some of the more interesting portions of the image. So this is without the giuliano 2 layer; this is with that giuliano 2 layer. An interesting effect that we're able to achieve by finding the differences between two filtered effects here inside Photoshop.
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