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Help on frame alignment with foreground subject crossing starscape

Discussion in 'Astrophotography' started by AG_Alex2097, Apr 12, 2016.

  1. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    Hey everyone, i've been struggling quite a bit with the alignment of a 10 stack astro photo, the problem is that i have part of the foreground slicing through the star scape which completely messes up Photoshop's Auto-Align-Layers, it works fine if i grab only a part of the starscape and mask out everything else, but apparently Photoshop doesn't perform a Euclidean Transformation on the full layer and simply warps the visible part of the layer (resulting all the masked areas (read: starscape surounding the chair lift) being misaligned)

    What i tried to circumvent this was painting a mask of the whole foreground, applying it to each layer and then trying to auto align, but the edges of the masked area also confuse Photoshop's Auto-Alignment

    I tried manually adjusting each frame using the warp transform tool with difference blending as a guide to the best of my abilities, but the nebula was all blurry (i should've saved those as examples now that i think of it..)

    I also tried DeepSkyStacker to align the images under a dual boot (which took forever) and it seemed to do a good job, but it doesn't like transparency meaning i can't filter out the chair lift from the frames

    Any tips on how you would align these? I've searched all over the web and tried a multitude of software applications, but all to no avail

    Is there no simple application that performs Euclidean/Rigid transforms on images to align them based on a couple of user defined reference points? (a couple of stars for example)
    DeepSkyStacker looks like it works this way (automatically selecting star ref points), but it has the transparency issue :/

    Here's 2 of the frames:

    Any help is appreciated!
     
  2. georgian82

    georgian82 Mu-43 Regular

    118
    Jan 17, 2014
    Hi there,

    I can try running your 10 frames on PixInsight and see what happens. You can upload them into Dropbox as raw format.

    If that works for you, let me know and send me a private message.

    Cheers
    Sebastian
     
  3. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    Thank you Sebastian, i'll shoot you a PM once the files have finished uploading, i'm curious if it will be able to pull it off without a mask though :eek:
     
  4. georgian82

    georgian82 Mu-43 Regular

    118
    Jan 17, 2014
    Not a problem. I can't promise it will work but we can try. Did you also shoot dark frames and bias frames by any chance?

    Also, can you post a picture after you stack it in PS to see what the issue is?

    Thanks
     
  5. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    No dark frames unfortunately, it was icy cold on that mountain and didn't want to spend double the time up there
    No bias frames either as until i started experimenting with all the software packages, i had never heard of it :/

    As for what happens:

    Method 1: Regular Auto Align on the starscape (with a handpainted accurate mask of the chair lift) and applying a median stack gives a small part of the star scape in focus, the rest is a blur (due to misalignment)
    Preview:
    79f4a0086fb06dc61273566ebcdbcb51.png

    Method 2: Applying the handpainted masks (therefor cutting the pixels with foreground), then adding a new, rough block-out mask that completely masks out the whole area of the chair lift (including large part of the starscape surrounding the lift), doing an auto align, then removing the rough masks and applying a median stack gives a much better result, but the starscape around the chair lift remains blurry (again due to misalignment)
    Preview:
    afd5f4266d164ab25a011a07368d2680.png

    Basically, what i need, is the correct alignment of the cut out frames that look like this:
    fd753d6e8496f8cb02fd50e3c5f566d8.png

    But the auto alignment of photoshop looks at those hard edges to align, resulting in a blur similar to method 1 (but worse)
     
    Last edited: Apr 26, 2016
  6. georgian82

    georgian82 Mu-43 Regular

    118
    Jan 17, 2014
    Thanks for posting the results of your attempts. Now it is more clear to me what the problem is. What was the exposure time of your individual frames?

    By the way, bias frames are really easy to take and they help remove readout noise from your light frames (actual pictures). Just cover the lens with a lens cap and set the shutter speed to the maximum level (1/400 or 1/800 depending on your camera) and leave all other settings the same as light frames (same ISO). Then take a sequence of 30 of them and stack them together to make a master bias frame. Temperature is not important in this case...they can differ form your light and dark frames.

    Cheers
     
  7. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    Exposure time was 30 seconds at ISO 1600 (at freezing temperatures, which probably helped with noise) with the Samyang 7.5mm f/3.5 wide open

    And yes, i did a quick read on bias frames, but i'm not quite sure what exactly is meant with "readout noise", feel free to enlighten me :)
     
  8. wjiang

    wjiang Mu-43 Hall of Famer

    Don't use Photoshop for UWA star alignment (especially fish eye) - it can't really cope with the complex transforms required to align stars appearing to rotate around a pole as viewed through a UWA or fisheye lens, because the edges stretch dramatically more than the centre of the frame.

    I use DSS to do two sets of stacks and manually blend them. One with star alignment - make sure you have reference stars from all over the frame otherwise with a UWA it will start blurring anywhere you don't have a reference. The other with no alignment - this should be fine to stack the terrestrial elements as you're using a tripod. Manually blend the two together in Photoshop.
     
    Last edited: Apr 12, 2016
  9. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    I tried DDS and it stacked the stars nicely, but the chair lift was shifted with each frame, causing a big blur on it, and masking the lift out before feeding it to DDS doesn't work because DDS unfortunately doesn't support transparency
     
    Last edited: Apr 13, 2016
  10. wjiang

    wjiang Mu-43 Hall of Famer

    I did not use any masking prior to stacking, you don't need masks in DSS because the merging is done in PS later.

    Stack once with auto align to align stars (foreground is blurred, don't worry this is fine), save as 32-bit TIFF. Then do a new stack with auto align OFF so the stars are all blurred but the foreground (i.e. chair lifts) are sharp, save as another 32-bit TIFF. Take your two stacked TIFFs into PS as layers, then merge them with masks - use the sky from the one with sharp stars and the foreground from the other. Save this 32-bit TIFF as your 'master' for further PP.
     
  11. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    It's difficult to explain, but the problem with a non-masked star alignment is the part of the foreground that slices the starscape, it also becomes a blurry mess that overlaps part of the star background that was originally around the slicing subject (in this case; chair lift), the sharp foreground you have has thin cables/ poles/chairs, so if you're going to mask merge the 2 frames, you will still end up with either the blurry lift from the star stack around the sharp lift, or you will end up with a blurry starscape around the lift because of masking it properly to the dimensions of the sharp lift, if that makes sense? probably not..
    I'll try to provide some pics of what i mean later ;)
     
  12. wjiang

    wjiang Mu-43 Hall of Famer

    I think I understand now. I've personally never had a problem with that for some reason, the transition region is so small that it's never that noticeable. The only thing I can suggest is to replace the slicing elements out in PS with blank sky (e.g clone stamp or content aware remove) before you stack the stars. That way at least the sky stack is clean. Since the chair lift is always in the same place you can even repeat the action on all your source frames.
     
  13. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    I suppose overlapping the lift with starscape is an option, but i'm not sure about the results it'll give, might have to go that way though, just unfortunate DSS doesn't support transparency :/
     
  14. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    As an update, in the end I went with Wjiang's suggestion of using content aware fill (that tool works gooooood!!! :eek: Thanks for pointing it out to me!) and blending the harsh edges by using the soft brush on a mask
    I made 3 edits, all of which i'm pretty happy with, but i'm not sure which one is the best, if anyone could help me pick, it'd be appreciated (and you get to see the end result:) )

    [​IMG]

    I'm guessing top left is the most natural one, but i kind of also enjoy the idea of the coloured ones, but maybe it's too much, i don't know :p
     
    Last edited: Apr 27, 2016
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  15. wjiang

    wjiang Mu-43 Hall of Famer

    Brilliant result! I'll have to keep that trick in mind if I end up with such issues. My pick would be the first one, I prefer my Milky Ways natural coloured, plus it gives a more interesting tonal variation - the others look too blue to me.
     
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  16. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    Oddly enough that was the last iteration i did, i think i got distracted too much on getting rid of the light pollution, but i do tend to agree it is the better one as it has the most color variation :)
    Thanks for the input!
     
  17. georgian82

    georgian82 Mu-43 Regular

    118
    Jan 17, 2014
    Great job! I am glad you were able to figure it out!

    I like the top left myself =)
     
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  18. Hypilein

    Hypilein Mu-43 Veteran

    286
    Mar 18, 2015
    Really good work. Prefer top left as well. I find the purple one nice too though.
     
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  19. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    156
    Dec 18, 2015
    Alex S.
    Cheers you all, wouldn't have been able to do it without you! :)