In this exercise I'm going to introduce you to the final blending options inside of Photoshop and those are the Luminance-exclusion slider bars. Now, what they allow you to do is drop out or force through the display of colors inside of your layers based on their luminance levels. We'll be working inside this file that's called Lunar madness.psd. It features this moon image which I've colorized but originally it came to us from David Woods and then we also have this kind of lightning ball rendering with these sparks here and that comes to us from Arga, both of the Fotolia Image library.
I'm going to go ahead and turn the lightning ball layer off for now. We are going to be ultimately blending it with the moon but before we do that, I want to demonstrate how these options work. So I'm going to turn on the gradient layer which is just the linear gradient going from black to white and back to black again. I'll go ahead and double-click in an empty portion of this layer to bring up the Blending Options dialog box and I'll move it offscreen a little bit so we can see what we're doing. Now, these are the sliders down here; the This layer slider and the Underlying layer slider. Now, they're frequently mislabeled the Blend If sliders which isn't actually true.
Blend If refers to this pop-up menu right here, and so basically you're saying, are you going to blend the luminance levels inside of this layer based on Gray which is the composite version of the image or based on the contents of the Red, Green or Blue channel? So you can decide that if you want to, almost all the time you just leave that set to Gray; otherwise, these sliders each have their own names right here. So this layer allows you to drop out luminance levels on the active layer. Let me show you how that works. Notice that this bar extends from black which is 0 to white which is 255.
So that's saying the entire continuum of luminance levels from 0 to 255 is currently opaque and so far as this slider bar is concerned. If I want to change things up a little bit, I could drag that white triangle over to left and notice as I do so that I am dropping out the brighter shades inside of this gradient. So currently what I'm saying is 0 is opaque, so black is opaque, and 175 is opaque, so fairly light gray. However, anything brighter than 175 is temporarily transparent.
So I can click OK out of this dialog box and then revisit it in the future and continue to adjust these settings. Anyway, the more I drag this slider over to left, the more I go ahead and reveal that moon in the background. It's almost as if I'm peeling back these drapes to do a reveal here, however it's all based on luminance. So now I'm saying anything 53 or brighter. So just about all of the gradient is turning transparent, and just the range from 0 to 53 is staying opaque. All right! I'm going to go ahead and drag that white triangle all the way back to the right and now I'll drag the left triangle to show you that I can also make the darkest colors transparent if I want to.
So at this point, I'm saying anything 159 or darker is transparent; from 159 to 255, everything is opaque. Now, the problem with this is you get some very harsh transitions. You end up getting a jagged effect, because it really is an either/or proposition. Either you have transparent pixels or you have opaque pixels, but if you look closely at these triangles, they have a cleft down the middle of them and what that's telling you is that each triangle is actually two triangles glued together. So here is how you peel them apart.
You press the Alt key or the Option key on the Mac and drag one-half the triangle and it comes apart from the other. Now you can go ahead and manipulate these two pieces independently of each other. So in this case we're saying anything from 0 to 102, so from black to a pretty dark gray is transparent. Anything from 188 to 255 so the lightest colors are opaque and anything from 102 to 188 is gradually becoming more and more opaque, or more and more transparent going the other direction if you prefer to think of it that way.
The other option here, I'll go ahead and reset this Black slider here. The other option that's available to us is this Underlying layer slider and it should really be called Underlying layers because what you're doing is you're revealing the composite view of all the layers under the active layer based on their luminance levels. So you're forcing through luminance levels here. If I drag the White slider over to the left, then I'm going to reveal the brightest colors inside the moon. I'll go ahead and restore that guy back to where it was and if I drag the black triangle over to the right, then I'm revealing the darkest colors inside the moon.
Once again, I can go ahead and peel either of these triangles apart by Alt+Dragging or Option+Dragging one-half or the other and then that goes ahead and softens up the transitions between those luminance levels. Now, something to bear in mind here is if you do one of these numbers, if you drag one of these triangles, one of these halves of the triangles back over to the other one, they'll fuse together and then once you start moving that triangle around, it moves as one. So you just need to beware of that happening.
If it does happen of course all you have to do is Alt+Drag or Option+Drag on a Mac in order to separate those guys apart from each other. That's how the Luminance-exclusion slider bars work inside of Photoshop. In the next exercise, I'll show you how to use these sliders to create a fantastic effect.
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