 All right, another thing I want to show you before we dive into processing here is just what a single sub looks like in each channel and then what it looks like after they're stacked. We'll see this a little bit as we go, but a lot of people just are curious about this up front. So keep in mind, this is just for this particular object, which is the seagull nebula or sometimes called the parrot nebula, IC 2177, but it's still illustrative, I think, of what you can maybe expect out of an object that emits in hydrogen alpha O3 and S2. So the first thing we're going to look at here is an H-alpha single sub. So this is one five-minute exposure with the ZWO ASI 1600 in H-alpha. Now let's look at after it's been stacked. So this is, I think, like 30 sub exposures stacked together. And so you can see there's a single, there's a stack. So a lot comes out in the stack as you increase the signal-to-noise ratio by stacking many together. Here's a single O3 sub, Oxygen 3. You can see there's just barely something there. This is a little bit hard to make out. Here's after we stack, and then it's a lot more evident where that O3 is. Again, I'll show you a single and after the stack. Okay, and then last, here's the S2 signal, so the sulfur. There's a single, oh, sorry, this is a single, got out of order, and there's the stack of the sulfur. All right, with that said, we can move on. All right, now we're going to start processing, and we're going to start with a program called Deep Sky Stacker. It's a free program. You can download it online, just Google Deep Sky Stacker. It is Windows only, but I know some people use something like Wine to get it on Mac or Linux, but I've only used it on Windows. There are alternative stacking programs, like SeqWater, I'm not exactly sure how to say it. There's also something called Open Sky Stacker, so if you are looking for something that isn't Windows only, there are alternatives, or you can try to get it working using Wine. Anyways, it's free, it works pretty well for registration and stacking of your images, if you're doing Deep Sky astrophotography. You basically just follow along here on the left hand side from the top to the bottom, so I'm going to start with Open Picture Files, and this is asking for my light frames. I've already organized everything here, so I have my lights, my flats, my darks, my dark flats. I'm going to go into the lights folder, start with the HA, go ahead and press Control A to select all the files and click Open. And if I scroll down here, you can see it's a bunch of files loaded. If I click Check All, I can see how many. Okay, so I have 32 HA light frames loaded. I've already gone through these and thrown out a few that I knew were bad, but I'll show you how you could do that in Deep Sky Stacker as well. What you can do is click on one, and then use this little histogram slider guy up here in the upper right, doing it pretty badly here, okay, there we go. And you can zoom in, I'm just using my scroll pad here to zoom in, look at the stars, and then you can move through, and it will keep applying that same histogram stretch. So you can get an idea of what each frame looks like to see if there's any that you want to throw out. Okay, anyways, that's the light frames, I'm going to go ahead and add my dark frames here, then add my flats, and finally my dark flats. Okay, so with everything added there, I'm not using bias, I have found with the ASI 1600, I don't like using bias frames, instead I just use these dark flats, which are just like darks, except they are timed so that they are the same exposure length as your flat frames. So I have 32 light frames, 15 darks, 29 flats, 20 dark flats. Seems okay. As long as everything's in the double digits, it will probably work pretty well. But since we are doing a complete narrow band image with not just the HA, but also the S2 and the 03, I'm going to load those but into different tabs down here. One thing that's not entirely intuitive, but it makes sense once you get used to it, is that down here it says main group. And if we were just doing like a DSLR stack in Deep Sky Stacker, this is all we would have to worry about. But since we are shooting mono and we want to separate out by filter, we are going to use this group 1 to add the next filter set. So main group, we are going to remember is all HA. I'm going to then click on the group 1 tab and go through the same process of adding first my lights, but this time for the 03, then my darks. These are actually the same darks, but it doesn't matter. Then my flats for the 03, and finally my dark flats for the 03. Okay, so now this is all 03 stuff. I'm going to go ahead and click check all. Okay, so now we have all of that. Deep Sky Stacker is actually smart to recognize that those were the same dark frames I loaded in the HA group, so it still says 15 right there. But you can see both the flat frames count, the dark plate frames count, and the light frames count have all increased. Okay, lastly, I'm going to now click on group 2 and add my S2 lights. I know this is all a little bit tedious, but I just want to show every step so no one loses track of what I'm doing here. Again the darks are the same darks that I used before because you don't need to shoot different darks for different filters since the camera doesn't know what, you know, if it's completely dark it doesn't matter what filter you're using. But flats you do have to shoot by filter just in case your filters were dirty and they had different dust patterns on them. Okay, so now I have everything loaded. I'm just going to go ahead and click check all again and just look through this. And normally what I would do now is I go into each individual frame and check it and make sure that it looks okay just by going through here. I'm just using my arrow key, my down arrow key to look through each frame and really you would want to actually look at the stars, make sure that you don't have any streaky stars in each frame. I'm just sort of abbreviating this process because I've already actually looked at all of these, but you'd want to look at every light frame and weed out any that were bad just delete them from the list. Oh this is actually a cool frame to show. See these, these are probably satellites or airplanes. Don't have to worry about those. If you see some frames that are fine except they have some of these streaks through them because of the airplanes or the satellites just leave those in because as long as you're using at least 10 subs that's not going to matter. Those are just going to average out. Alright, so let's just say I've looked through all the light frames now I'm going to go back to my main group here. Now at this point we don't know what is the best reference frame to use. So the cool thing about Deep Sky Stacker is after we register all of these pictures it will give each picture a score and we can pick the picture that has the best score to register all the other frames to meaning that it's going to use that frame to assign any offsets. So if something is a little bit shifted we know that they will actually because I used what's called dithering so it's moving the pictures around purposely. It's going to then take one frame and register all the pictures from all three filters to that frame. So I'm going to go ahead and click register checked pictures. I'll leave all of these settings alone but I'm going to turn off stack after registering right now because I just want to register and then look at the score of each sub. Under advanced tab here I'm going to go ahead and click on this compute the number of detected stars. This gives me an average in the HA tab of 540 stars. That's a perfectly acceptable number. If you have hundreds of stars that's good. My feeling is if you have like something like 10,000 stars you probably want to lower the threshold because then it's going to just be doing too much work trying to find the patterns. If you have like under 100 stars that's probably you probably want to raise the threshold a little bit. Actually really anything above like probably 50 stars will work but if you have like under 10 stars it's probably going to fail. So that's just sort of a ballpark. I'm not exactly sure about those numbers but you just want to always I always go into this advanced tab and press that just to sort of make sure that everything is looking fine. But usually with this default 20% it usually works fine. Okay, I'm going to go ahead and click OK and then it's immediately going to start calibrating. It's taking all of the dark frames right now creating a master dark frame. I'll just let it do that and then we'll see what happens next. Now creating the master dark it does all kinds of just with the default parameters it does kind of all kinds of averaging and throwing out outliers. What this median Kappa Sigma means is that it looks at a standard deviation of all the values and throws out outliers that just seem like they're not in every picture. You want this because you want your master dark to be a true standard for what the dark current is in your camera. So now it's doing the same thing for the dark flat frames. I'm going to probably go ahead and just fast forward in the video through this because it's a little bit automatic you don't have to worry about it too much and I don't have much too much else to say but basically what this is doing is it's taking all the individual subs and condensing them down into masters. So you have a master dark a master dark flat and a master flat for each filter it then calibrates all the light frames per group or per filter and then assigns each sub a score based on the signal to noise ratio and the roundness of the stars. So we'll let it do its work here it's probably going to take like an hour or something and then we will come back and move on to the next part of this which is stacking everything based on a single reference frame. All right it's done registering all of these and has given everything a score. I'm going to go ahead and sort it by score just by tapping my mouse right here on the word score twice. And so what this does is now I can see that frame 18 has the best score 8679. And if I scroll down here I can see the worst H.A. frame has a score of 4110. I don't know exactly what this score means but in terms of the number but just higher numbers are better. So I'm going to use the frame that has the highest score to register everything else. If I look at group one which is the 03 that doesn't have a higher score look at the S2 that doesn't have a higher score either. So the H.A. is going to be the one that I'm going to use and specifically this one that has the highest score frame 18 to make it the registration master frame I'm going to right click on it and sorry not registration master reference frame that's for the deep sky stacker terminology. And so I'm going to right click on it and choose use as reference frame. When you do that you'll notice that over here in score there's now this little asterisk next to it. So you can remember that that is your reference frame. So now when I register it's going to use that one. I'm going to go ahead and click uncheck all. Okay. Next I want to just register all of my H.A. frame so I'm just going to go ahead and select everything here right click and check. So I have everything in the main group checked nothing in group one or group two then I'm going to go into stacked check pictures. It lets me know you know I have the darks I have the dark flat I have the flats and I can go into recommended settings here and just look through it's using Sigma Clipping it's using blah blah blah. Okay I basically just use the recommended settings automatic alignment I typically don't mess with things in here but if you want to mess around you can there's a lot of different options but I think that the defaults are usually pretty good. I'm just going to use standard mode for stacking. Okay and I'm going to click okay again and let this do its thing. So when it says computing offsets what that means is it's taking all of the different H.A. lights and using the reference frame to register all of these different light frames and it's already created master darks master dark flats and master flats so you can see that it just used the masters that it already created and right now it's already going in and stacking all of the lights together so this actually shouldn't take that long. You can see the estimated time remaining here under two minutes. The part that takes longer was that first step where it was actually creating all of the master calibration frames and then calibrating all the lights for each filter. This is actually a pretty quick process by comparison just creating your master H.A. light is what you can think of it as. Notice now it says angle 178 degrees what happened there was there was a meridian flip meaning that it the frames on the second half of this are almost 180 degrees different than the the first one because we changed from the east to the west side of the meridian. Okay now it's loading our final auto save.tiff you can see where it's located right up here some other videos I've seen on deep sky stacker will suggest you now mess around with this and apply and save off that picture and then go on to photoshop or gimp or whatever it is you're using there's really no reason to do any processing in deep sky stacker and actually if you read the instruction manual it says this is basically just here as a convenience so you can sort of see what your data looks like it's not meant as a thing for actual final processing. But if we now go back into the folder the H.A. folder you can see in addition to all of these pictures we now have auto save.tiff I'm going to go ahead and pull that out of the folder and rename it here as H.A.tiff another thing you can do instead of doing it that way is you can choose save picture to file over here and just make sure that embed adjustments in the saved image but do not apply them is the option checked rather than apply adjustments to the saved image and then you can just call it something haffinal.tiff and save it wherever you want I'll just save it to the desktop so either way you can just you can choose save picture to file and just make sure that this embedded adjustments in the saved image but do not apply them is the option or you can just rename the auto save either way will work but you don't you definitely don't want to make any adjustments in deep sky stacker and apply them before you save the final stack. Okay let's go back here. Okay so next we're going to do the 03 and if we look back at the main group here we can see that everything is unchecked but I still have this little asterisk I'm going to go into that means this is the reference frame that it's going to register everything against I'm going to go into 03 and if everything isn't already checked I'm going to go ahead and check everything again the way you can do that I'll just do uncheck all click on the first frame shift click on the last frame then right click and choose check. Okay for some reason I don't have the dark frames loaded anymore so I'm going to go back in here into the main group and also check all my darks just click and shift click and check okay so I have those 15 dark frames 25 light frames from the 03 30 flat frames 20 dark flat frames. Okay now that I have everything I needed for the 03 stack checked and I am going to be registering against this HA reference frame again that's really important that for each filter you're using offsets against the same reference frame so that when you put all three filters together into a full color image they're all stacked together correctly I can now go over here to stack checked pictures and there are some things that are not so great about deep sky stack or terminology because when it talks about registering frames to a reference frame it uses the word offsets but then it also uses the word offset for bias so when it says no offset right here it's talking about there's no bias frames loaded but that's fine because we're not using bias frames we do have darks dark flats flats and of course lights 25 03 lights so basically we're just repeating this process now for the 03 I'm going to click okay again it'll go through do its thing and I'll check back in a second here okay the 03 is now stacked you'll notice that up here it saves it to the HA folder the reason is that for whatever reason deep sky stacker thinks that the autosave should always go into the same folder that the reference frame is in any case I'm just going to use the save picture to file command down here under processing make sure that this embed adjustments in the saved image but do not apply them is the option that's checked and call this 03 final and click save okay so now if we look at our progress here we have the HA final the 03 final tiff you'll notice that the little preview on each of these is black that's perfectly fine do not worry about the fact that you're not seeing anything in these yet other than maybe some really bright stars because these are not yet stretched we'll do that in the next step lastly though we have to go back here to register checked images one more time go into or click uncheck all to uncheck all the 03 files go into group two which is the s2 frames click on the first file scroll down shift click on the last file right click choose check go back here to our main group and check all of the darks click shift click right click check so 15 darks I only got 15 lights on s2 that's okay normally I try to get 20 but 15 is okay 30 flat frames 20 dark flat frames okay so that's all set again it's still going to register against our reference frame which is here in the main group HA and let's go ahead and click on register checked images nope sorry stack checked images okay no bias frames that's fine we're going to be stacking an hour and 15 minutes of s2 all sounds good let's click okay and it does its thing okay now we have the s2 done again it saves it to the HA folder but we can go ahead and just go to save picture to file make sure that the do not apply the adjustments is checked and save this as s2 final tiff to the desktop we're going to minimize deep sky stacker and this is what we want to see when we're all done a HA o3 and s2 all 16 bit tiffs all stacked calibrated and registered we're now going to go ahead and move on to the next step in this case we're going to open up GIMP you want GIMP 2.10 at least depending on when you're watching this video they may have released newer versions but I know that in 2.10 it can handle 16 bit processing I'm going to go ahead and choose open as layers go to my desktop pick these three files that we just created these three tiff files we go ahead and turn off the visibility of the o3 and s2 just start with the HA and I'm going to go up here to the colors menu and choose levels and I'm going to start stretching this image okay choose levels again reset my black point but also move the mid slider over a little bit okay go do it again again reset my black point I'm just sort of looking at where the histogram is here okay do it again color levels reset my black point just move the mid slider over it's just this iterative process you just do this a few times levels reset the black point and each time I move the mid slider over a little bit less this time it's just a little bit in I'm just going to do it one more time color levels reset the black point okay I lied I'm going to do it one more time this time I'm just going to do the black point over perfect okay so that's stretching it's you're going to see that it works much better in GIMP compared to doing it in deep sky stacker using just the levels command there and I'm just going to repeat this process now for the o3 colors levels you start with the mid point slider bring it over then each time you reset black while bringing mid over till you have something like this where the o3 is showing nicely okay I'm going to turn on my s2 do it one more time colors levels start with your mid bring it over okay so I'm literally just doing the same thing resetting my black point over and over again using the left side of the histogram here while bringing over my midpoint to stretch out the signal so now I'm just going to look at each one looks like each time I left the sky a little bit brighter so I'm going to go ahead and reset the black point on each of these actually that looks fine let me trick the HA I'm just going to bring up the HA a little bit okay so the point is each of these looks like they have about an equal stretch now in terms of the sky background looks similar now what I'm going to do is I'm going to go up to colors go down to components and choose channel mixer no that's not it I'm sorry I'm going to go up to colors go down to components and choose compose and if you hover over this it says create an image using multiple gray images as color channels which is exactly what we want to do for the red I'm going to choose the s2 layer for the green I'm going to choose the HA and for the blue I'm going to choose the o3 this is sh0 processing so the red is the s the green is the h blue is the o I'm going to go ahead and click okay we'll open up a new tab with our new color image after it composes them pretty awesome huh so uh first thing I notice is that we have some registration artifacts here because the my rotation angle wasn't perfect so along the edges here we have some things that are sort of ugly I'm going to go ahead and get rid of those using the crop tool just right here or you can press shift c to get to it and I'm just going to cross each edge here and getting as much of the picture as I can while cropping okay it looks good I'm gonna go ahead and press enter to crop it very cool okay uh really the only thing else that I want to do with this is just play around with the curves and colors now um not much else you have to do this is actually I think a pretty fine image as is I could just save it right now but I'm gonna go ahead and play around just a little bit with curves first I'm going to bring my black point in a little bit I'm going to bring this up then I'm going to take this down a little bit this just improves the contrast a bit um it's sort of a modified s curve um um we don't necessarily have to bring this so far up if we want to do a little bit more modest go ahead and click okay all right the other thing I've noticing about this image is that it's pretty green um this is typical of just straight show imaging um sh o because the you're usually your h alpha channel which you assigned to the green is much stronger than the o3 and s2 signal so you get a sort of greenish image some people are fine with this I think it looks pretty cool actually but if you wanted to turn it less green how would you do that in gimp um this so when you take out some of the green that's typically called the Hubble palette and the way you do it in gimp is we're going to go back to colors channels colors components sorry but choose the channel mixer and with this if you have preview on you can really do a lot to change the colors just by messing around with these different things here so in the green channel I'm going to take out some of the green and just like that you go from a pretty um show looking image to a more Hubble palette image so you can see all I did there was I went from 1.0 on the green to 0.5 so about having the amount of green in the image makes it look much more Hubble palady if I increase the red in the red channel then that brings out these golden tones even more and if I increase the blue in the blue channel you can see then the then the o3 signal really pops um the one issue with doing this is then your stars go go pretty magenta I don't know of a great way to fix that in gimp but gimp is the software I am least experienced with so if you know of a great way to fix magenta stars in gimp please let me know in the comments and other people can find that as well okay so if you wanted the Hubble palette look this is how you would do it the channel mixer I'm going to go ahead and click cancel just to show you back what the just straight show look looked like a little bit more green maybe a little bit less contrast but I think it's a pretty interesting look um and that's really all I have to say about processing show images in gimp it's really just about getting good data putting it together making sure you're using all your calibration frames when you're all done you can choose file save as if you're planning to return to it you can save it in the gimp format when you're all done and you want to save it to the web you can choose file export and I'm going to go ahead and save that to my desktop as a png all right now we have a cool looking seagull nebula in the show format again if you wanted a more Hubble palette image with gimp all you'd have to do is go to colors components channel mixer and play around with this I'm just going to take out some of the green channel click okay and I'll save this one as oh I mean export this one sorry I'll export as Hubble all right that's it for this video if you have any suggestions for future videos please let me know and my website is at nebulaphotos.com here at the end you're going to see my Patreon subscribers if you're interested in becoming a patron you can check out the link right below this video thanks so much for watching