 Hey everyone, this is Nico Carver from nebulaphotos.com. Hopefully you've already watched part one of this series where I showed you how to capture a bunch of photos of the Orion constellation. Now we're going to jump into processing those photos with two programs, one called DeepSkyStacker and the other called GIMP. If you're following along with me, you can download these from Google Drive and just follow along with my example files here, or if you're doing it on your own, I would recommend organizing your files into these four folders. So you have them all ready to go for the next step here, which is we're going to use DeepSkyStacker to calibrate the lights with the flats, darks, and bias files, and then we're going to register those lights, which means match them based on the star patterns, so that they're all lined up and then stack them into one complete image that has all of that data combined together and it rejects a lot of the noise both through calibration and just through the process of stacking the images together. We can reject a lot of things like hot pixels and just the inherent noise of the sky and the uncertainty of light. So we're ready to go here. Let's go ahead and open up DeepSkyStacker, which is this right here. I'm using the 64-bit version. It does tell me a newer version is available for download. I'm using 4.1.1 and this says 4.2.3 is available. I'm not going to upgrade right now, but I think it works the same way. We start over here on the left-hand side and we just basically step through these different steps. We start with open-picture files and I'm going to navigate to that folder I was showing you before, a Ryan 85 millimeter, and I'm going to start by loading in my lights. I'm going to press Ctrl A to select them all and click open. Okay, now those are all loaded. I'm going to go ahead and check all of those just to see how many we have here. We have 451 lights. I'm now going to go up here back up towards registering and stacking and choose dark files. Go into my darks folder here. Again, click once and then press Ctrl A to select them all and then click open. Okay, we loaded in 31 dark frames. I'm going to click on flat files. Load in my flats. Ctrl A to select all. Click open. Load it in 20 flats. I don't have any dark flats this time. I'm going to use bias. So click on bias files. Open up my bias folder. Press Ctrl A to select everything and click open and we loaded in 60 bias frames. Okay, so we now have everything we need here. Lights, darks, flats, and bias. The next thing I'm going to do is I'm going to click on this register checked pictures link right here. We can see here there's an actions tab and an advanced tab. It says dark flats and bias checked. That's good. I'm going to leave automatic detection of hot pixels checked. I'm going to go to the advanced tab and I'm going to compute the number of detected stars here. Okay, it found 200 stars with a 20% star detection threshold. That seems fine. If I wanted to I could try raising that and then just try clicking that compute button again to see what happens. Okay, when I raise the star detection threshold that number of stars goes down. If I lower that star detection threshold like let's say to try 15% we get a few more stars. This is probably fine. I'm going to leave that at 15%. I'm going to click into recommended settings and just see what we have here. It's saying that we're using sigma clipping combination method and sigma clipping median for the other calibration frames. That all seems fine. Basically if this recommended settings thing found any problems instead of showing in green it might show things in red to fix certain things. With this all looks good. We can click on stacking parameters here and just see what it's doing. It's doing a median kappa sigma clipping. You can hover over these different stacking modes to find out what they do. This all looks fine. I'm going to click OK and I'm going to click OK again and it will start creating all of our master calibration frames. It starts with the bias then goes on to creating the master flats and the master dark and everything else and then it will go ahead and calibrate everything and register those checked pictures together. Once we have all of that done we can pick the best light frame to use for the final registration and stacking and then stack all of these pictures together. I'm going to let this go for a while here and check back in when it's done. It's now done. I'm going to go ahead and sort these by score. You can see the top score here is 1,862. That means that this has been when Deep Sky Stacker looked at all the different lights it found that this one had the roundest and tightest stars in terms of focus. I'm going to go ahead and choose that one as the reference frame. I'm going to right click on it and choose use as reference frame. We now get this little asterisk right there. I'm then going to go over here to stack checked pictures which is the next thing down and it looks like I didn't take my bias frames that is the same ISO as my darks and flats and lights. That's not good but oh well it's too late now. Probably work out fine. You can see the total exposure here is about 15 minutes because we took 450 frames at two seconds each at ISO 1600. I don't want custom rectangle. What is that? I just want standard mode. I don't know what I did there. There's an option to stack based on a custom rectangle and I must have somehow messed up and put that in. So you always want to check all these things. Make sure that it's what you actually want. I just want a standard mode where it's framed based on the reference light frame which we just set. I'll use Kappa Sigma Clipping. That's fine. All these other things are fine. Let's click OK. I'm just going to click on recommended settings and just check through here. Looks good. Okay one thing to keep in mind when stacking a lot of DSLR frames like this 450 is that it can temporarily use up a lot of space on your main hard drive. This is just because it uses a temp folder while it's doing this work. So you can see that this is going to use 62 gigabytes of my 80 gigabytes free on the C drive. So that's just something to keep in mind. You might need a fairly large amount of free space in order to stack a lot of frames at once like we're doing here. But I seem to have it now. So let's go ahead and click OK and let it do its thing of stacking these all together. Okay it's done stacking. Doesn't look like much here but that's because it's not stretched really here. So we're just seeing the bright blown out parts. But we can see a Ryan's belt there and things like that. But we're going to do the stretching in other programs. So all we have to do now is make sure that it's saved the auto save dot tiff which if I look in my lights folder here scroll to the bottom. There it is auto save dot tiff. That's all we need actually. So we're going to use that in the next steps and move on to the actual post processing programs because this was just what we call preprocessing. So it's calibrating registering and stacking and then we'll actually do the fun part right now. All right now that we have our images calibrated registered and stacked using deep sky stacker. We're going to move on to post processing the image that came out of deep sky stacker which is this auto save dot tiff in GIMP which stands for GNU image manipulation program. It is a free and open source project. It's been around for a while. It's a similar kind of program to Photoshop. But the main advantage is that it doesn't cost any money and also being open source you can contribute to it or fork it and make your own project. I downloaded the latest version of it at the time of this recording which was 2.10.14 and it's April 4th 2020. So let's open up the program and let's open up our auto save dot tiff file. So I'm just going to go to file open and I put it on my desktop here and then I'll click open again. OK. And it doesn't look like much right away. This is because it's not yet stretched and what we mean by stretch is we're going to transform the values in the picture applying sort of a curve that takes it from this linear state to a completely nonlinear state where we stretch out the histogram. Typically this is done if you just shoot JPEG in the camera with something that's built into the camera that converts the raw picture values to a pleasing picture with a curve. So before we apply that first curve though let's go ahead and duplicate our layer. You can do this by just going over here to the layers panel on the right hand side right clicking and choosing duplicate layer. And I'm also going to rename that layer just by double clicking into there and selecting the text. I'm going to call this first stretch. OK. Now we can go up to the colors menu up here at the top and choose levels. I want my preview turned on which is down here in this version of Gimp it's turned on by default but I'm not sure if that's true in all versions. So just make sure your previews turned on and then take this middle slider here and push it over. The image will become sort of gray that's normal and just click OK. And I'm going to repeat that process. I'm going to go back to colors. Levels. But now what you can see is we can now see this histogram bump right here. This is most of the information in the picture. And what we're basically trying to do is broaden that hump of information so that we have more dynamic range in the picture. And we're going to do that by moving this shadow slider into the right and this history the middle slider to the left. And we're going to have to probably do this a few times to get to where we want it. This time I'm maybe just going to reset my black level mostly like that. And if you want to zoom in you can either use the view menu and there's some zoom options right there or you can just use the keyboard shortcuts which are plus and minus. So if I just press plus which is actually you have to hold down the shift key and hit the plus equals button. I can zoom in and this can help see the detail in the picture and see what we're bringing out. So I can see that I can already sort of see the flame Nebula there and Orion's coming in nicely. And so sometimes it's nice to zoom in like this while we're doing this stretching. And if I move the black point slider all the way sort of over right to the edge of where this histogram bump is right now I can take a look at what we can see. And I know that we should be able to bring out the horse head a little bit better than that. So I'm going to bring my midpoint slider over again. We're going to keep doing this a few more times and sort of see it coming in now. You can see now that the histogram mountain here is getting really quite spread out which is what we want to see maybe just a couple more times. That's something up there. Cancel that one. We go ahead and zoom back out with the minus key. Yeah. OK. This is I think at a good point. This is going to be my final stretch for now. Again I called this first stretch so we might do a little bit more stretching later on but this is this is a good starting point here. The first thing that we can see is that we've now brought out the Orion Nebula quite well. We can see both the core and the outer edge of it here. This right above it is called the running man Nebula. And so what did I just do? I clicked on that accidentally. And then up here we have the horse head. Let me try to zoom in on that a bit right in there and the flame Nebula. The next thing I want to do with the image is try to crop it a bit. And then after we've cropped it I'm going to get rid of some of this gradient. All of the interesting stuff in this image is right here in the Orion constellation. And out here it's not as interesting. If we if we zoom in on on the corners we can see there's actually a lot of misalignment and weird stars and things out here too. So we might want to just crop that out of the picture. So I'm going to choose my crop tool here. It's the second row all the way over to the right. And I'm just going to pull out a crop box. Something like that with Orion roughly centered. We're keeping in this bright star Rigel which is of interest. Yeah, I think that looks good. So I'll just press enter or return to accept the crop. And now we have less weird stuff to deal with. And this this gradient looks a little bit more manageable too. And that's the next thing we're going to deal with is is trying to remove that gradient a bit. So I'm going to actually duplicate this first stretch layer twice. I'm going to call this one. Now actually I just duplicate it once for now. And we'll call this bg newt for background neutralization. But right above that background neutralization layer, I'm going to create a new layer just a new blank layer. And in GIMP the way to do this is look down here at the bottom of the layers panel and all the way over on the left is this little icon with the plus sign. Go ahead and click that. And we just want a new visible layer. That's good. So click OK. And nothing in the image changed because this right now this this layer is transparent. You can tell that because we have the checkerboard pattern over here in the thumbnail. But we're going to fill this transparent layer with a gradient to create the gradient. And what the gradient is going to be is going to model the background sky. So disregarding the stars and the nebula, which is what we want to keep in the image, we're going to try to model this light pollution effect. That's why it's it's brighter down here at the bottom is because light pollution is almost always worse the closer you get to the horizon line where cities and human civilization is and it's it's better up here. The further you get away from the city lights. So we're going to try to model that with a gradient. To do so, I'm going to pick my color picker, which my color picker tool sorry so if I look over here in the tool set, the second row, second from the left is my color picker. I'm going to set I'm going to set the foreground color first. So for the foreground color, I'm going to pick something up here at the top. And then I'm going to set my background color down here. Oh, I know what I did wrong. Sorry. Let's try that again. So I'm going to first click on my background neutralization layer over here. So that's what we're going to be sampling on. And then with my color picker, I'm going to first click up here. And you want to be maybe sure that you're not clicking on a star. So if you accidentally click on a star, you're going to get a weird result. See what it did to my foreground color there. It made it this sort of pinkish color. What I want to be clicking on is the background sky. And so see there again, I think I clicked partly on a star and that's why we get that bright pink there. So just click around until you get this sort of sky looking value. Then we're going to do the same thing for the background color. So over here in the color picker options, I'm going to choose set background color over here on the left. And then I'm going to go down here to this corner. So I think is the brightest corner. And I'm going to choose a sky value down there. Let's click around a little bit till I see one looks nice and bright. That looks pretty good. Okay, and then we're going to draw out a gradient using this foreground and background color. So let's choose our gradient tool here. Which is this one. You can also get to it by just pressing G for gradient. If you are new to GIMP, and this is like, you know, you just started up just like me, then your gradient will be in its your gradient tool we are using in its default state. And in its default state, it just picks the foreground and background color to create the gradient here. If yours doesn't look doesn't do that for some reason, then just click on the swatch here, the gradient swatch and choose custom. And then what it should do is do a foreground to background RGB gradient. But you want it to click this, we want a linear shape. We want foreground to background and we want it to be a custom gradient. And then we're just going to draw a line from the foreground to the background in the image. And what I mean by that is from the top of the image to the bottom because that's how we picked those two colors. So I'm going to just do it from where I picked that color, which was up here in the upper left of the image down to the lower right. And when I look at that, my gut reaction is that's not quite right. But let's just go ahead and turn. Oh, I should have me undo. One thing I should have mentioned here is we wanted to be doing this actually on the blank layer right here, let me just actually call this gradient so I remember. Okay, so make sure you have the gradient blank layer selected. And when I just did that, I noticed that it didn't look quite right. There was a little bit too much blue over here. Well, actually, this is a fairly up and down gradient. So I'm actually thinking that blue isn't quite right. Let's try actually switching out our color samples and picking one more in the middle here. Yeah, it's a little bit darker and a little bit more in the middle here. So I'm on my background neutralization layer, I can reset these just to see if I can get a little bit better result. Okay, then I'm going to go back to my gradient tool, make sure I have my gradient blank layer selected over here. And let's try this again, just going from the top to the bottom this time rather than from corner to corner. Okay, I like this a lot better. This is looking right. And notice if I move this sample up, that's going to reposition where it's sort of changing from dark to light. So I think maybe ending it right about there looks about right. And I'm just going to press Enter to accept that. Let's go ahead and try turning the visibility of that gradient layer off and on to see how it looks. That looks pretty good. Next, what we're going to do is we want to subtract this gradient from the layer below. The way to do that is we're going to change its imaging or its layer mode. So right here in the layers panel, we have mode and right now it's set to normal, meaning that whatever is on top here in the layers panel is what's showing. But we're going to change it to subtract, which is down here, not quite at the bottom, but oops, there we go. Okay, so you can see this made a really dramatic change to the image. It looks immediately a lot more dramatic because the sky background is now dark, because we subtract it out that light pollution through this gradient removal process. If I turn it off and on, there's before, and there's after, before, after. And really, this is probably going to be the most important thing I show you in this GIMP tutorial that really just what we've done so far, the stretching and the gradient removal, everything from here on out is really more optional, I'd say. If we zoom in now, we can see that everything already looks pretty nice. I think the star colors look pretty good. The see the horse head and the flame and the Orion running man here. Down here, got the bright star Rigel. If I'm looking here at the at the very bottom of the image, you can see that we still have a bit of residual brightening. And it's sort of greenish looking, maybe greenish yellow looking. Same thing over here on the left hand side. If you just decided, you know, there's nothing really that important to me in the image on those on the side in the bottom, maybe I would just do some further cropping. So if I think, you know, the I still think I could crop in a little bit further this this this side in the bottom here don't really matter. I guess grab my crop tool again and crop those areas out. I'm going to undo that just to show you another option. If you if you'd like the framing, you know, this wider framing better is we could just apply another background gradient removal. So to do this, let's just first merge this gradient subtraction down into the background new player. So to do that, just with the gradient layer selected, go up to layer and choose merge down. What that means is it's going to combine it with the layer below it. Just like that. So now we've we've made that that decision permanent. We could undo, of course, but we've basically combined those two layers. Let's now go ahead and duplicate the background neutralization layer and call this I don't know, bg newt two. And I'm just going to repeat the process. So I'd make I'd make a new layer. Click on bg new to pick my color samples. And this time, I'm going to try to get rid of this brightening over here in this corner. So I'm going to pick my color picker tool. I'm just going to go from out here for my foreground to down into this corner for my background. Those look pretty close. Maybe I'll be for my foreground. I'll go somewhere out here. I wonder if that little pink means something different than I think. Maybe it just means this is black. I don't know. Okay, let's try that. So grab our gradient tool, go up here to the blank layer. And let's just draw a gradient down into this corner. Yeah, that looks cool. So it's basically saying out here, don't really do anything down here, let's subtract some of this greenish crap. Okay, I'm going to press enter to accept that gradient. And then I'm going to change this to subtract mode. And it did a it did it did its job. But it went a little bit too far. So what I mean by that is the opposite of green is magenta. And now this whole corner looks to me a little bit magenta bluish, rather than a more neutral black. So what I'm going to do is I'm going to play around with the opacity of that layer, which I should name here, just call this corner, until this is looking more neutral. Okay, I think that's pretty good. So I'll go ahead and just merge that layer down into bg new two. So layer merge down. And then we can turn that layer off and on and see what it did. Before fairly extreme green cast over there. After still a little bit of a color cast, I'd say it's a little bit more of like a bluish magenta now. But I think it's a lot less distracting than that green cast. And if we kept fiddling with it, we could probably completely eliminate it. Since this is just a quick tutorial, I'm not gonna not gonna keep going with that. But if you if you're really, you know, have some time, you could just keep fiddling with the technique I showed you to really neutralize the background more. Next thing I'm going to do is I want to just select the bright parts of the image to basically the stars in the nebula to increase the saturation on them a little bit. So I'm going to go ahead and duplicate this layer again. And I'll call this new one saturation. And I'm going to choose select by color. There's also a tool. So select by color tool, same thing. It's the fifth tool over. Here's the tools options right here. I'm going to choose to feather the edges. But just by, let's say, one pixel. And where it says select by composite, I'm going to choose select by lightness, because we just we don't really care about picking a particular color, we just want everything that is bright in the picture. And then I'll just click on something bright in the picture. I'm just going to click on Orion nebula here. And you can see that then it made initial selection of many of the stars and the bright parts of the nebula. But you can see it's not yet picking up on some of the dimmer nebula. So I'm going to raise the threshold and click again. And now it's picking up on a lot more. Let me go ahead and zoom in to check this out. Yeah, I think that's doing a pretty good job. You can see it's picking up on the stars, not picking up on the background so much. See how it's doing on these nebula. Pretty good. Okay, zoom back out. Now with all of this stuff selected, I'm going to go back up to my colors menu. I'm just going to choose the saturation command. And I'll increase the scale here. It's a little hard to see because of the selection preview. Probably some way to turn that off. I'm not sure. We zoom in a little bit here. Okay, let's just try turning the preview off and on. Okay, let's try increasing the scale a lot more. I guess I can see it starting to work. Alright, let's apply it. Okay, here's where we can turn off so show selection. Let me go ahead and turn that off a second. And I'm going to turn my saturation layer off and on to see what it did. There's with it off. There's with it on. Okay, I think that's pretty subtle. Let me try zooming in a bit. I can definitely see a difference, but it's it's pretty subtle. Let's view the selection again to see if it's still active. Okay, it is. So I'm going to turn the selection off. And let's go back to colors. This time I'm going to try hue saturation. And let's just see if this one is a little easier to see the difference. Yeah, I think that one is working a little better. So let's try to turn the preview off and on that we can go even a little higher. Another thing we can play around with here is the lightness. Let's see if we make the light parts lighter. Yeah, I like that actually makes it pop a little bit more. It's basically like increasing contrast because we're not increasing contrast to the sky background, but we are increasing the brightness of the stars and nebula. Okay, so I've just increased saturation and lightness on our selection. I'm going to click okay. And you know what, I'm pretty much happy with this. I'm not going to do much more with it at the moment because I think it looks pretty good. There probably is, you know, other things we could do. But I like how this looks. So let's go ahead and save it. If you if you think you're going to come back to it in GIMP, you just want to choose file save and save it in the XCF format called Ryan here. Okay, but if you're saving it as anything else, then you'll go to file export and by default, GIMP exports in PNG, which is a good choice. It's it's doesn't lose much information that way. There's a bunch of little things you can choose, but you don't need to just click export. Okay, there's the Ryan PNG on my desktop. The one downside to the PNG format is because it is fairly lossless, meaning it's not losing much information, the file sizes are quite big. So this is 43 megabytes. So if we wanted to save it instead in JPEG, we could do file export as and just change the ending to JPG. And then it's set to recognize the file type by extension. So then we click export. And it gives us a different set of options here. Instead, we have this little quality thing that's going to be how much it compresses the image. I'm just going to do 85 and export it. And because JPEG is a lossy format, that got it down to 4.3 megabytes. But I think it will still be of perfectly acceptable quality. Let's go ahead and make that full screen. Okay, and there's our final result. If I was going to critique it a little bit, some of the stars are a little bit magenta so we could work on the color balance there. There's still a little bit of a sky gradient, especially over here on this side and down here in this corner. But other than that, I'm pretty pleased with this considering it is just an untracked simple shot of the Ryan constellation. We pulled out the bright belt stars, Rigel, a Ryan and running man, the horsehead nebula, the flame nebula. And there's actually a little bit of another one up here. This little guy up here is m 78. Just a nice little reflection nebula up there. You can you can clearly see the horse head in there. And then this one is called the flame. They're they're surrounding this bright star called only talk. Well, I hope that this tutorial showed you that even with free software and minimal gear, you can get a nice pleasing deep sky astrophoto. And if you like this kind of video, please subscribe and turn on notifications. I'll also just say that I have a Patreon which you can support me and help me keep making these videos till next time. This is Nico Carver from nebula photos.com.