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In the previous two movies, we saw calculations being shown. Now, what we're going to do is look in that window and look at it a little closer. Let me go right into my channels. I am going to create a brand-new channel. There is nothing is selected, so it's automatically black. I am just going to set up a little situation here. I am going to give myself a nice big feather of 20 pixels, and I'll create a shape right here. And this shape is going to represent a light coming in from some doorway somewhere. So I am going to go ahead and fill that selection with the background color, which right now is a white. There it is.
I am going to create another alpha channel, and this alpha channel is going to have a light coming in from a window somewhere, like that, which we'll fill with white. And let's do another one right here, which will be the same kind of thing, just light from the window somewhere, like that, and we'll fill that with white. So there, it has two channels: the doorway light and the window light. So now I want these guys to work in certain ways. Now when I apply this to the image I'll throw in the whatever reflections, the colorizations I need for that light coming in from outside.
And then whenever I need to do something for the doorway light, I'll just choose that alpha channel and apply my effects onto the image through that alpha channel. But then there are times when the two of them should work together. Like for instance, the area where the two highlights overlap each other should have a certain effect on the image, especially if the light coming from the room is a colored light and the light coming from outside is a bright white light. So therefore, the effect where they intersect is going to mean something different.
So what will happen is I go into Calculations and I will take both channels: Alpha 1 and Alpha 2. Right now, I am subtracting one from the other, but what I want to do is have that place where they intersect. So by changing the blending mode, I can go in there and say what I really want is Multiply. By Multiply, I am selecting the area where the two of them overlap each other. Send that to a new channel and it becomes a completely separate channel that shows me the area where these two light sources are intersecting.
Let's say I wanted them to work together as one, the two different channels working as one in unison, so I can have yet another effect on my image. Well, in this particular case, I'll go back to Calculations and I have 1 and 2. And when you look at this you might say, well, add might be the one to do, so you can see what Add does. Add isn't quite right because you see that blotch that just happened? What's happening with Add is let's just say we had a 30% pixel right there in one channel and a 30% pixel in the other channel, the result is a 60% pixel.
So in a case like this where you don't want to override the lightest color so what we do is we say Screen-- screen one on top of the other-- now you can see that we have a perfect blending between the two alpha channels becoming one channel that takes into account both channels. Send that to a new channel and we have yet another channel that sees the different channels put together into one. Now looking at that Calculations, there are a lot of things in there. I strongly suggest that you sit there and play. There are many different modes, including these two, which don't appear anywhere else, Add and Subtract.
All kinds of modes that have different effects on what one channel would do on top of the other. You can Invert the channels in the process and even add another channel as a mask as you're applying an effect to different channels, many different steps. And the best way to learn this is to actually sit there and play with those, push all those buttons and see what they do. Work with different channels on top of each other and see the effects that you're going to get. And those masks that results from all these calculations can have really intense effects onto your image.
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