Intro to Narrowband and Hubble Palette, Pt. 2b - DeepSkyStacker and GIMP

alright 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 IC2177 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 gonna look at here is an 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 subexposures stacked together here’s a single oh three sub oxygen three you can see there’s just barely something there it’s 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 order and there’s the stack of the sulfur single and stack all right with that said we can move on all right now we’re gonna start processing and we’re gonna 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 seek waiter 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 Astro photography you basically just follow along here on the left hand side from the top to the bottom so I’m gonna 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 gonna go into the lights folder start with the AJ go ahead and press ctrl 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 ok so I have 32 H a 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 here 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 gonna 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’ve 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 and but since we are doing a complete narrowband image with not just the HA but also the s2 and O 3 I’m going to load those but in two 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’re shooting mono and we want to separate out by filter we’re gonna use this group one to add the next filter set so main group we’re gonna remember is all a che and then click on the group 1 tab and go through the same process of adding first my lights but this time for the o3 then my darks these are actually the same darks but doesn’t matter then my flats for the o3 and finally my dark flats for the o3 okay so now this is all oh three stuff I’m gonna go ahead and click check all ok so now we have all that deep sky stacker is actually smart to recognize that those were the same dark frames I loaded in the H a group so it still says 15 right there but you can see both the flat frames count the dark light frames count and the light frames count of all increased ok lastly I’m gonna now click on group two and add my s2 lights you 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 if your filters were dirty and they had different dust patterns on them okay so now I have everything loaded I’m just gonna 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 would want to look at every light frame and weed out any that were bad just delete them from the list well 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 these streaks through them because of the airplanes of satellites just leave those in because as long as you’re using at least 10 subs that’s not gonna matter those are just gonna average out all right so let’s just say I’ve looked through all the light frames now I’m gonna 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 - 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 H a 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 a hundred stars that’s probably you probably want to raise the threshold a little bit if you real actually really anything above like probably 50 stars will work but if you have like under 10 stars it’s probably gonna 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 gonna 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 I’ll show you and we’ll see what happens next it’s now creating the master dark it does all kinds of just with the defaults parameters it does kinds of averaging and throwing out outliers what this medium Kappa Sigma means is that it it looks at a standard deviation of all the values and throw 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 what am I trying to say a true standard for what the what the dark current is anger camera so now it’s doing the same thing for the dark flat frames I’m gonna 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 gonna take a look 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 gonna 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 eighteen has the best score eight six seven nine and if I scroll down here I can see the worst h.a frame has a score of 4-1 100 I don’t know exactly what this score means but in terms of the number but just higher numbers are better so I’m gonna use the frame that has the highest score to register everything else if I look at Group 1 which is the O 3 that doesn’t have a higher score look at the s 2 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 mastery reference frame that’s 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 and 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 ok next I want to just register all of my H a frames 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 1 or group 2 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 its using blah blah blah okay I basically just use the recommended settings automatic lineman 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 gonna use standard mode for stacking okay and I’m gonna click OK 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 you created master dark semester 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 the 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 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 this 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 autosave 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 autosave TIFF I’m going to go ahead and pull that out of the folder and rename it here as each a TIF 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 a final dot 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 embed adjustments in the saved image but do not apply them is the option or you can just rename the autosave 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 oh three 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 gonna go into that means this is the reference frame that it’s going to register everything against I’m gonna go into o3 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 ok 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 though three thirty flat frames twenty dark flat frames okay now that I have everything I needed for the oh three stack checked and I am going to be registering against this H a reference frame again that’s really important that for each filter you’re 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 whites 2503 lights so basically we’re just repeating this process now for the o3 I’m gonna click OK again it’ll go through do its thing and I’ll check back in a second here okay the oh three is now stacked you’ll notice that up here it saves it to the H a folder the reason is that for whatever reason keeps guys 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 O three final and click Save okay so now if we look at our progress here we have the H a final the O 3 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 O three files go into group 2 which is the s 2 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 15 darks only got 15 lights on that’s - that’s ok I’d normally I try to get 20 but 15 is ok 30 flat frames 20 dirt flow frames ok so that’s all set again it’s still going to register against a reference frame which is here in the main group H a and let’s go ahead and click on register checked images no sorry stack checked images ok no bias frames that’s fine we’re gonna be stacking an hour and 15 minutes of s to all sounds good let’s click OK and it does its thing okay now we have the s2 again it saves it to the H a folder but we can go ahead and just go to save picture to file make sure that do not apply the adjustments is checked and save this as s to final TIFF to the desktop you know minimize deep-sky stacker and this is what we want to see when we’re all done eh-eh-eh o 3 and s 2 all 16-bit Tiff’s 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 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 go ahead and turn off the visibility of the O 3 and s to just start with it H a and I’m going to go up here to the colors menu and choose levels and I’m going to start stretching this image ok 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 ok do it again color levels when you set 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 one more time colored levels reset the black point okay I lied I’m gonna do one more time this time I’m just gonna do the black point over perfect okay so that’s stretching its you’re gonna see that it works much better in GIMP compared to doing it in deep sky stacker using just the levels command there I’m just going to repeat this process now for the oh three colors levels you start with the mid point slider bring it over then each time you reset black while bringing a mid over till you have something like this where the o3 is showing nicely okay I’m going to turn on my s to do it one more time colors levels start with your mid bring it over yeah 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 I’m just gonna 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 looks fine let me trick the 8hj I’m just gonna bring up the hitch a a little bit like that 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 you know that’s not it I’m sorry 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 H a and for the blue I’m going to choose the O three this is SH Oh processing so the red is the S the green is the H blue is the oh I’m gonna go ahead and click OK it will open up a new tab with our new color image after it composes them pretty awesome huh so 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 gonna 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 across each edge here give me as much of the picture as I can what cropping okay it looks good I’m gonna go ahead and press enter to crop it very cool okay really the only thing else that I want to do with this is just play around with the curves and colors now 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 herbs 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 it’s sort of a modified s-curve we don’t necessarily have to bring this so far up if I want to do a little bit more modest go ahead and click OK alright the other thing I’m noticing about this image is that it’s pretty green this is typical of just straight show imaging Sh oh because the you’re usually here each alpha channel which you assigned to the green is much stronger than oh 3 and s2 signal so you could have 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 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 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 hats halving the 39:03 - amount of green in the image makes it look much more Hubble palette II 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 O 3 signal really pops the one issue with doing this is then your stars go pretty magenta I don’t know of a great way to fix that in GIMP but GIMP is the prof 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 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 OK and I’ll save this one has no I mean export this one sorry I’ll export as Hubble alright that’s it for this video if you have any suggestions for future videos please let me know and my website is at nebula photos.com here at the end you’re gonna 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 .