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If you're shooting a night sky and you want star trails, you are always going to have a problem with the background of the sky, the ambient section of the sky, brightening up a lot. Here are two images that I shot in Eureka Valley, part of Death Valley National Park. Here's what I did without star trails, and then I did a 30-minute exposure with star trails. This one in the left here is about a one-minute-long exposure. And you can see that in addition to having a long enough exposure to capture wonderful smeary stars, it also really brightened up the background of the sky.
And so it makes the star trails less impressive. They are kind of washed out by the ambient light in the sky, and a lot of that light is coming from the fact that the sun had set over here. You can see it right here. Just in case you're wondering, these streaks through this part of the image are airplanes that were flying by at the time. And notice here you can see the Milky Way. The Milky Way even shows up over here as this bright streak of light right here. There is not going to be anyway of getting the rid of that. Actually, I kind of like that it's there. This is a real easy edit to make; you just need Levels adjustment layer. The tricky bit is getting it to the blend properly with the foreground.
The foreground, by the way, is, I had a campfire burning and so that was casting a lot of light in the foreground. That's why it's all red. I'm going to make a new levels adjustment layer, and then I'm going to just crank the black point up to really try and beef up the contrast in the sky. As long as I am doing that, I might as well move the white point also. But I've got to be more careful with that because that's actually brightening the ambient temperature. I'm going to try the midpoint to get some of those midtones. No, I don't like that. In fact, I'm going to take the midpoint adjustment the other direction.
Now what I'm kind of riding here is I'm watching these stars in here, I don't want to lose too many stars, so this is a little bit tricky. I want the sky darker, but I don't want to take out some all the actual information that I want there. Something else I don't like about this image is I don't like the red tinge that it's getting. I'd like to take that out. But first let's do with the fact that I'm now darkened the foreground so much that it's unintelligible. I've got my mask over here. Right now it's completely white which means the entire image is getting the levels adjustment.
I would like only the upper half to get that adjustment. Your first thought might be well, Oh no that means I've got to get a paintbrush and paint around every one of these tiny little details here on the horizon. You don't have to do that; you can really fake this very effectively by using the Gradient tool. This is the Gradient tool right here. If you're not seeing it, it may be because it's hidden underneath the Paint Bucket tool. This is what's here by default. If I just click and hold on the paint bucket, it pops on into this little menu and I can choose the Gradient tool. I want to be sure I have a gradient set from white to black, and I want to be sure it's a linear gradient rather than a radial gradient or one of the other options.
I've got my foreground color set to white, my background color set to black. Now I'm going to come over here and I'm going to start where I want the gradient to begin, and I'm simply going to drag down to where I want the gradient to end, and when I let go, it does this. Now if you're not clear on what's happened here, take a look at my mask. I've got white up above, so my levels adjustment, which is darkening the image, is being applied at full strength, all through here all the way down to about here, where it starts ramping off to no adjustment at all. So that's creating a smooth transition from completely adjusted to not adjusted at all.
And fortunately, it's the nature of the horizon that it is a gradient. So, I'm just kind of hiding that transition in what should be a natural transition in the sky anyway. That said, I think I missed. I think there's a little too much brightening right in here, so I can just redefine the gradient right now. I don't have to erase anything. I'm going to start at the top of this mountain here and drag more down into here. I'm just going to a little bit lower than I was before. That's going to cast a little more of the image into darkness. The great thing about this is these mountains were already in silhouette, so I'm hiding the transition in an area that was already black.
So I think that's looking pretty good. I've got my brightness where I want. Let me give you a before and after. That's before, that's after. More dramatic stars this way. But let's see what we can do about this reddishness. I'm going to up here to my Levels palette and create a Hue/Saturation layer, and I'm going to target these red tones. They are more orange tones, but I'm going to hit Reds here and then grab this eyedropper and click on maybe the brightest red in here that I can find. Now I can de-saturate this area and just take some of the color out.
If I wanted, I could go a little bit further and even shift to the hue. If I look over here, I see that the sky is pretty blue. If I wanted, I could try shifting more towards blue. It's going to be a really difficult edit to pull off and I actually like this warm color that's in here. I'm going to just put that right in there. Problem is I have now de- saturated my foreground too much. I can fix that again with pretty much the same gradient that I used before. I'm going to grab my Gradient tool, drag down into here, and that's brightened this back up--or not brightened it back up; that's re-saturated it.
And in fact, now that I see it re- saturated, I realize that actually it's a little too saturated. I would like this to not be quite so red. So if I look at my mask, I see I've got white at the top with a smooth gradient going into the black. So full desaturation here and then starting about here and less and less and less, until here where there's no desaturation at all, and so I'm getting the full original orange. I can now grab a paintbrush and a shade of gray--I'm going to pick somewhere in the middle here--and if I brush in here, I'm now painting over the black area with gray.
In other words, I'm adding a little bit of that desaturation that I dialed in. So here I am mixing painting techniques within a single mask to build up this more complex mask that's white on the top, a gradient through the middle, and then just these areas here where I'm adding a little bit of desaturation. And you can tell that my mask is a little bit sloppy. It doesn't matter. These areas around here, they're mostly shadow. They're mostly black, so I can't see how saturated they are. So, that works pretty well. Let me give you a full before and after here. I'm going to turn off both adjustment layers.
You can see this is my original image and now with both the Levels and Hue/Saturation layer, I get this, so I think that looks a lot better. These are pretty typical techniques you'll need to do on probably any of your long*exposure sky shots. You may not have the color shift here that I've got. You may have a sky that after you do your levels adjustment comes out looking way too blue. Let's do the same thing I did with my Hue/Saturation adjustment layer here, but instead of targeting reds, target blues, and you can pull out some of that super-saturated blue that may get in there and get back to a more natural- looking sky.
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