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The third part of the popular and comprehensive series Photoshop CS6 One-on-One follows industry pro Deke McClelland as he plunges into the inner workings of Adobe Photoshop. He shows how to adjust your color, interface, and performance settings to get the best out of your images and the most out of Photoshop, and explores the power of Smart Objects, Shadows/Highlights, and Curves for making subtle, nondestructive adjustments. The course dives into Camera Raw to experiment with the editing toolset there, and returns to Photoshop to discuss toning, blur, and blend modes. Deke also teaches tried-and-true methods for sharpening details and reducing noise, as well as creating quick and accurate selections with Quick Mask, Color Range, and Refine Edge commands.
In this movie, I am going to show you a terrific use for the Difference blend mode. Basically, it is the go to mode any time you are trying to find the differences between a couple of images, and that's because if a pixel on the active layer is the same color as the pixel behind it, then the composite pixel turns black, which means that anything that's not black is at difference. So let's say I am trying to create a screenshot of the Gradient Mesh feature inside Adobe Illustrator, and I went ahead and drew these two peppers, and now we're seeing the mesh points throughout.
And in my case, they are showing up as orange against a red background, which isn't a terrific amount of contrast. Now, I could have changed the color of those points in Illustrator, but I wanted still more control than that. What I wanted to be able to do was dim the peppers back, like you see them here, and then turn the points black, so that there is no ambiguity whatsoever, whether I show this image on screen, at my Web site, or whether I put it in one of my books, you can see those mesh points. So I'll go ahead and switch back to the image at hand.
Here's what we've got. I took one screenshot of the peppers with the mesh point selected, and I took another screenshot of the peppers deselected, and then I went ahead and set one on top of the other, and with the gradient mesh layer selected here, I'll go ahead and switch the blend mode from Normal to Difference, and we end up getting this effect here. So you can see everything that's not part of the mesh becomes black, and only the mesh lines remain. Now we need to turn all the differences white, so press Control+Shift+Alt+E, or Command+Shift+Option+E on the Mac, in order to merge the composite layers onto a new layer, and I'll call this new layer merged, and then you need to apply two adjustments.
You go up to the Image menu, choose Adjustments, and choose Desaturate, or if you loaded dekeKeys, you can press Control+Shift+Alt+U, or Command+Shift+ Option+U on the Mac, and that goes ahead and gets rid of all the color. And then you go up to the Image menu, choose Adjustments, and choose a command we haven't seen so far, Threshold, which allows you to turn all pixels on the active layer either black or white. And the reason this feature is called Threshold is because this slider triangle right there represents the threshold. If I take it down to, say, 110, then anything with a Luminance level of 110 or brighter becomes white; anything with a Luminance level of 110 or darker becomes black.
You can see we have got this tiny little histogram right there. We need to move the slider triangle all the way to the left of it. I ended up going with a Threshold level of 30, but I could have selected 20, for example, and gotten exactly the same results. As long as I'm inside of this area, it doesn't matter. All right. So I'll click OK. I've now got the white mesh point lines; everything that's not a mesh point is black. I want to convert that mesh to a selection, so I'll switch to the Channels panel, and press the Control key, or the Command key on the Mac, and click on RGB, and that goes ahead and selects anything that's white, and deselects anything that's black.
Now I'll switch to the Layers panel, turn off both merged, and grad mesh, so we are just seeing the no mesh versions of the peppers. I'll press Control+Shift+N, or Command+Shift+N on the Mac, to create a new layer. I'll call the layer mesh lines, and then I'll press the Enter key, or the Return key on the Mac, and I will press Alt+Backspace, or Option+ Delete on the Mac, to fill the selection with black. So we now have the black mesh lines. Go ahead and click outside the selection in order to deselect it, and now let's go ahead and give this no mesh layer a special treatment, so that it fades back, and I am going to do that using a layer effect.
So click on the fx icon, choose Color Overlay, and then click on the color swatch, and I recommend you change the Saturation to 0, and then change Brightness to 90. We need it to be bright, but something less than white. So 90% will work. Go ahead and click OK, and then switch the blend mode to Luminosity, so that we take out the luminance, but we leave the color behind, and then to bring back some of that luminance, I reduced the Opacity value to 70%, and then click OK.
And we end up achieving that effect that we saw at the outset of the movie in which the mesh lines are clearly distinguished from the artwork in the background. And that's one of the many ways to use the Difference blend mode in order to find the difference between two mostly identical images.
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