Astrophotography: The ABSOLUTE BEST way to STRETCH your Astro Image data in Photoshop [PS]!

so here we are in photoshop and i want to show you the absolute best way to stretch your data in photoshop at least in my opinion and it's a technique originally developed by mark shelley called the arc hyperbolic sign stretch and i'm going to post in the description his website where you can read his explanation of how this arc hyperbolic sine stretch is implemented in photoshop how to apply it in photoshop uh the reasoning behind it and also some presets for your curves you'll need the arc hyperbolic sine curve presets um it's a zip file you can download off his website then you can apply this technique that i want to show so here is mark shelley's website photoshop color preserving stretch so he was originally the guy who wrote the pixen sight arcsin hyperbolic stretch module for pixensight and so pixon site users get this real easily and if you look right here he gives a link for the curved presets for the arcsin hyperbolic function curves and once you download that you get a bunch of these curve files and you basically place them in your photoshop directory and he gives you the link right here as to where to place those but uh this is his website and i'll put the link in the description so the reason for the arc hyperbolic sine stretch is it doesn't desaturate your color data as you stretch and it doesn't cause stars to bloat and the stars maintain their color it's the absolute best way to stretch your data in photoshop in my opinion and so let's go ahead and start so this is ngc 7822 stack um it's in 32 bit so the first thing we have to do is change the mode and make it a 16 bit per channel image using in the method box here the exposure and gamma defaults and so once we've done that the idea would be to duplicate your layer and create what i call this channel mixer layer because right now i have a green color cast because my asi 294 mc pro has an rgb sensor so i have two green pixels per red and blue and so if you look at the histogram my green channel is pulled way ahead of my red and blue and so we need to align these channels in other in order to get a better color balance and so what i do is i apply adjustment layer from channel mixer and in the red channel here and the blue channel i'm going to make adjustments and in the red channel i'm going to adjust the green and in the blue channel i'm going to adjust the green and basically what happens is i pull um from the green and boost my red so if i just go here to the green channel box within the output red channel and i boost that up you can watch the histogram the red will increase and what happens is i'm slowly approaching alignment with the overall green channel and basically what i want to do is where this yellow is currently showing up it's where the red and green are mixing and i basically want that yellow to be centered within the red so then i want to go to my blue channel and i want to boost the green part of my blue channel and as i do that you can see that my blue channel is now coming to alignment and when they all mix together i get gray in my main histogram showing that they're uh mixed right in the center and so then i hit okay and you can see that my image is now um a lot more color balanced and uh each of my channels red green and blue are now aligned so the next step is we need to do a levels adjustment and so if you select the channel mixer layer and hit ctrl alt shift e it will stamp everything in your previous layer onto a new layer this creates a non-destructive workflow so that you can access previous layers work in case you really mess up or you want to go back to where you started from and so this i'm going to rename to levels and if you hit control l it will bring up the levels box and the thing here to do is we want to stretch or sorry not stretch adjust our levels by starting with the black point basically pulling it right to the point where you see that data start and hit okay and then we continue to do this ever so slightly right at where the data starts on the black side this way we don't clip any of our black data and so we can do this in rgb but we can verify in the red green and blue as well if there's a certain part or certain channel that needs um adjustment to bring us right up to the edge of where the black point is wanting to be set and we just continue doing this until we've got the data the black point set as close as possible to the main spike in our histogram [Music] do [Music] and so i'm just once again continuing to adjust that black point as fine as i can and it looks like the green and blue channel need a little more adjustment than the red channel because the red channel is packed with uh hydrogen alpha data because i use a triad ultra filter here and so once again this doesn't clip my my black data it just brings my black point as far as i possibly can bring it without clipping data there we go so i think i'm as far as i can go and if we look at the histogram here you can see everything's to the far left maybe on my green i can go up actually one yeah there we go all right okay so this is where things get interesting and we begin the stretching process so the first thing is to stamp your data forward so ctrl alt shift e and we're going to name this gray multiply and what we're going to do is go to image adjustments hue saturation and we're going to make this about this layer gray by putting the saturation all the way down to minus 100 hit okay and now we have a gray image and then we're gonna stamp that layer forward ctrl alt shift e and we're gonna make what's called a gray divide layer so it's just a copy so in the gray multiply under this setting here normal we're going to change that to multiply and in the gray divide we're going to change that to just a divide and so what we're going to be doing is applying our stretch to this gray multiply so what the multiply and divide does is it prevents us from bleaching our data as we stretch our data the color saturation maintains through each stretching iteration and we don't get bleach out data or bloated stars and our stars look really nice when we do this type of stretching and the color data is preserved in our stars as well as in the overall data so one thing that happens is there's an artifact due to photoshop where the data looks funny and so it's because the cache doesn't update properly so you have to go to at least like 67 zoom value to actually see the correct uh data being displayed so now once we're in this gray multiply we can actually begin to do our stretch so the idea is to preserve the color ratios in the gray multiply channel and then divide by the unstretched luminance data and in order to do this the first thing we need to do is select the gray multiply hit control m and then we want to select a preset default of the arc hyperbolic sine curve preset and so there's different ones uh from increasing curve to a very very very um powerful curve at the arcsin hyperbolic 1000. so i stick with the arcsin hyperbolic 10 and as i do that you can see my data will become stretched and at this point you can see the hyperbolic function um being applied as a curve then you hit ok real refresh the the histogram here and you can see that a levels adjustment is required so you hit control l and all my channels will be the same now because we're preserving the color ratios and so i can just focus on the rgb channel and adjust the black point such that i don't clip any of the black data and continue to do that until i've adjusted my black point as much as possible so i think that's probably good maybe a tad bit more i can stretch this data or sorry not stretch correct the levels and right there i think is good and then what i do again is hit control m and i apply another hyperbolic sine 10 stretch and my data once again is further stretched i hit okay refresh my histogram and you can see that a slight levels adjustments needed ctrl l and increase the black point and do it again to make sure that see if i have anything left to adjust in the levels maybe just one there refresh my histogram and we can see that i'm have the black point pushed as far as possible now and i'm almost done with stretching getting close now i'd apply the hyperbolic sine 10 again and see my result and see if i can still have room for adjusting the black point and i do so i'll hit okay but i can see i'm starting to bring out a lot of noise but my stars are well preserved and so i'd hit control l again and adjust my black point let's see how this looks at control l again see if i have any room i think that's probably the max i can do it there and i don't think i'd want to stretch point past this point here now and you can see all my channels are completely the color ratios are preserved so if i hit ok here now if i go to the grade divide and i do a ctrl alt shift e and stamp it forward i can zoom out now to look at my my total stretched image for my data so for me personally this is just a starting point of where i would um continue to process much much more in depth this is just a very raw image with very flat contrast and there's a lot of detail to be brought out with further manipulations however what's interesting at this point since i have a triad ultra filter is to look at the differences in the channels here's the the red channel contribution this is the hydrogen alpha so you can see there's a lot of good hydrogen alpha data in here then the green is the oxygen three and then the blue is the hydrogen beta and you can see there's not much difference between the hydrogen beta and the oxygen three however there is some differences if you if you look at certain regions with lots of details in between them as you switch back and forth you can see some slight differences but uh major difference in that in the hydrogen alpha so like i said this isn't um the end this is actually just the very very tip of the beginning this is just how i stretch my data and you can see that the stars look really good in terms of not being bloated or bleached while the data the nebulosity looks stretched and you can see faint details to deeper details so very very very great technique for stretching your data so thanks for watching this short tutorial and hopefully i'll see you next time with a video similar to this [Music] you

Channel: AstroEd's Astrophotography Channel

Views: 19,713

Keywords: astro image processing, processing astrophotography images, processing astrophotography in lightroom, astrophotography image stretching, stretching astrophotography, linear to stretched data, raw image processing in photoshop, image processing in photoshop, image processing, how to, deep sky stacker, how to stretch astrophotography, photoshop tutorial for beginners 2020, photoshop space photography, space photoshop, space photos, astroed, astroed's astrophotography channel

Id: CGac5XvSsJs

Length: 15min 57sec (957 seconds)

Published: Wed Oct 14 2020