Star Stacking: Layer Masks
When you think back to your basic composition, bright areas of the scene always draw your eyes. The highest saturated part of the scene always draw people's eyes. And so does contrasty areas, so when we're crafting our images within Photoshop or Lightroom, we don't want the brightest things to be distractions from our scene. Certain cases, they can work, but generally, notice that I painted this so that this would be the brightest thing in the scene. So this is our general attraction, but then the next place my eye goes is down to these areas 'cause they're kind of bright, but really where I want you going is back into here. So if I was to take an adjustment layer, let's say curves here, and I'm gonna put that at the top, which it did not go to, because I was on a different layer. I'm gonna wanna grab this and bring this all the way up to the top. Now it will adjust everything. So when I adjust this curve, now what I'm gonna do is sort of darken down, and if I do that, of course, it's ...
happening to the entire image. So what I could do is paint out the areas that I don't want, which is kind of pain, because what I'd actually have to do is paint out everything up in here and that would take a long time. But what I could also do is just go to this layer and I can hit ALT delete and that would be ALT option delete. And that, what it does, is it fills with the foreground colors, so if I wanted to fill it with white, I would hit command or control delete, if I wanted to fill it with black, I would hit ALT delete. Now, this change isn't coming through anywhere and the only place it will come through is where I paint with white. So I grab my paintbrush and flip flop my color to white, and I can go down in here and paint this lower area in where it got a little bit too bright. Alright, that's a bit heavy handed, I feel, so I'm gonna go back and make an adjustment. Maybe make it not so much so. And if I feel like this got too dark now, which does look a little bit unnatural, I'm gonna click on the mask again to insure that I'm actually painting on my mask and I'm gonna use my brush tool and I'm gonna paint black, but instead of using 100% to paint, I'm gonna tap my five key on my keyboard and that gives me a 50% opacity and now I'm bringing some of that back. So we always here that white allows the change to come through, and in this case the change is the curve. Black doesn't allow it to come through, while gray allows some to come through. And there's too different ways you can paint gray. The first way, and let me just go back in time here. The first way is to choose black and use a 50% opacity, and what that will do is fill in that white, which is the painting I just did, but if I go into the black it doesn't ruin it. Alright, let me undo that, by hitting command z or control z. Now the other way to do it is by actually choosing a gray. And so I could double click on the foreground icon and choose somewhere about a middle gray. Click okay, now same color, whoops, first of all I gotta change my opacity back to 100% so I'm tapping zero. Same color gray, but if I go into the black, that actually paints gray over the black. So two different methods for getting that gray on the mask, it just depends on what you're wanting to do. In this case my choice was to actually choose the foreground color of black with the opacity of 50% so that if I went out of the lines, I wouldn't mess up the rest of the mask. And again the whole goal there was to let some of that change come through and some of it not, 'cause it just got a little too dark in this corner. And I could even do the same thing in here, maybe go down to 30% and take some of that out there, just to kind of brighten that up and you can see how you're creating these different tones of gray on the image. Alright, so I'm gonna ALT click on my mask again to return that to the view and there's our finished image. Really wasn't hard at all. As a matter of fact, the easiest part of it was blending the stars together. It took me more time to actually darken down this area then it did to blend the stars. So that's a great technique, folks, for being able to control the foreground light and the amount of light painting you're gonna do in the frame by star stacking rather than doing one long exposure.