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All right, in the previous exercise when I told you that the Difference mode goes ahead and subtracts the active layer from the layer below and then applies an absolute value thereby creating a psychedelic inversion effect, that may not have sounded like the most practical blend mode to you. In fact, it's an exceedingly useful mode. You can do things with Difference, you just can't do otherwise. For example: Here I am working inside this file called AIcs5 1on1 figure.psd. The title refers to the fact that this is a figure that I am making for my Adobe Illustrator CS5 One on One book from Deke Press and O'Reilly Media.
All right, so what I wanted to do here for the screenshot was I wanted to separate out these gradient mesh lines from the image itself, so that I could change the color of the lines if I wanted to and otherwise modify them to my hearts content. So what I have got going in Layers panel? Not much, but I've got a points layer, I'll go ahead and turn it off, and you can see that the no mesh layer contains no mesh, we're just seeing the image and this is a screenshot that I captured on one of my Macs. And so somehow I managed to lift those points and those points are by themselves on that independent layer, so now we're just looking at the points layer.
How did I get that? Did I sit there and meticulously trace those points? Absolutely not! That would've been the biggest waste of time. And also it wouldn't have worked out very well, I wouldn't have been able to draw these fluid lines along with all these points even if I thought that was a high time. So this is what I did instead, I am going to turn that points layer off so I can show you how I made it, and then I'll turn this layer called difference on. And right now we're not seeing any special Blend mode. If I click on there, it's set to the Normal mode, but this is a screenshot of that very same image with the gradient mesh lines visible.
So I basically shot the image with the mesh lines and without the mesh lines. You need to shoot it both ways if you're going to do something like this, and this is just one example of the kind of things you can do. All right, so I'll go ahead and turn that layer back on and now what we can do is using the Difference mode, we can find the differences, because I was telling you all the like colors are going to cancel each other out and turn to black and all we're going to have left is the unlike colors. So with the Difference layer active, I am going to go to the Blend mode menu there and I'm to choose the Difference mode and we end up getting this effect.
Look how well it works, its just absolutely 100%... peels out all of that information. All right, now I can do anything I want with it. So, first thing is I need to enhance the contrast so I can easily grab these points here. So I am going to press the Escape key so the Blend mode is no longer active here on the PC and I'm going to press Ctrl+Shift+Alt+E or Command+Shift+Option+E on a Mac in order to create a merged version of those two visible layers, and I'll go ahead and rename it merged. Then I want to make everything that's not black white so I am going to go up to the Image menu, I'm going to choose Adjustments and I'm to choose the Threshold command.
And I'm got to find the threshold which will be over here someplace; you may recall that Threshold finds a threshold along your Luminance levels beyond which all of the colors are either white or black. So as I move the slider triangle over to the left, I am making more and more colors white year, because this entire range of histogram junk right there is turning white and that represents the various colors that were associated with the points, a moment ago. This black area, this line along the far left hand edge, indicates the black region where I had similar colors and we've got a big huge gap in between so I can set the threshold to any of these values and get away with it here, and then I'll click OK.
And that goes ahead and makes the points white and the background black and then I need to convert that to a selection. I just go over to the Channels panel and Control+Click or on a Mac Command+Click on any one of these channels because they are all identical at this point. We're seeing the composite view of the image after all. So I'll just Ctrl+Click or Command+Click on the RGB composite. That goes ahead and selects all the white, deselect the black, because the dark thing is its own mask. I'll switch back to the Layers panel, I'll make a new layer by pressing Ctrl+Shift+N or Command+Shift+N on the Mac, and I'll call this my new points because I want it to distinguish it from the old points layer, click OK.
And now what I'm going to do is I am going to a turn off merged, because we don't need it anymore, and I'm going to turn off the difference layer because we don't need it anymore either. And notice that I've got the selection outline exactly in the shape of my points so I am going to press Control+H or Command+H on a Mac, I didn't deselect the image, I just hit the selection outlines and I'm working on this brand-new independent layer. My background color is white so I am going to press Ctrl+Backspace or Command+Delete on the Mac and now I have this independent layer of points and that's all there is to it; Ctrl+D, Command+D on the Mac to deselect and now I can edit these points independently.
And the primary way I might to edit them, I'll turn this layer off for a moment, turn Difference back on, let's go and set it back to the Normal mode by pressing Shift+Alt+N or Shift+Option+N. And the primary reason I did this is because these points are blue and they don't show up very well and I could have changed there color if I wanted to inside of Illustrator to make them show up better, but this was much more flexible way to work. And of course, you know, if I really had issues, I could add, for example, a Drop Shadow behind my new points if I really needed them to standout.
And I'll go ahead and do that just so you have a sense of how flexible this approach is. I'll select that my new points layer, the independent points above the no mesh layer and I'll go ahead and choose Drop Shadow from that FX icon and I'll add a slight drop shadow to my points. So I'll take the Distance value down to 2 and I'll take the Size value down to 2 as well and we can see the small drop shadows between each and every point and line on this layer. I could even increase the Opacity value if I wanted it to standout better and once I'm done I would go ahead and click on the OK button.
So one of many practical applications of difference anytime, you want to find the difference between two very similar versions of an image. Use that mode, extract the differences, do whatever you like with him. In the next exercise I'll show you a practical application for Divide.
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