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  1. #1
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    Default Fustrated with my incompetence in image stacking



    Evidently I am just an idiot. I keep trying to get reasonable images and something always goes wrong. Anyway, here is my latest tests to try to learn what the heck I am doing...

    I spent one night imaging NGC6992, 30 lights (ISO800, 480sec), 15 darks, 15 flats, 15 bias. Here is what the original lights look like, unedited except for resize:



    Now I run them through DSS and that gives me this:



    That was the default, no adjustments of any kind. Then I take that and run it through photoshop and use levels to create this:



    Not happy with that, and continually fustrated with DSS I download the trial for Maxim DL and stack the same images with it, that fails so I convert all the images to TIFs and that works to create this:



    I load that into photoshop and again use levels to create this:



    Better I think, but then there is this image:



    That is a single frame, not stacked, no flats, no darks, no bias, only 480 seconds of exposure, played with in photoshop.

    Now here is where things get really interesting. All these images were processed on the same day in roughly the same manner (I did not track how much I moved each slider exactly, I just tried the same technique to each one until they looked as good as I could get them).

    Here are some closeups, 1st up is the Maxim DL image after processing in photoshop, cropped to a small section:



    Here is the same crop from the image stacked with DSS:



    And lastly, here is the single frame cropped:



    Now I was under the impression that taking four hours of images, stacking them with darks/flats/bias files would substantially improve my images, and yet I like the single image better.

    For DSS I have tried Average, Kapps-Sigma and Auto Adaptive stacking methods using a variety of different options (except I learned 2x drizzle errors out) and for Maxim DL I used the tutorial on their site for standard stacking. Maxim DL provides a better output image than DSS at default settings but still does not approach the quality I see in the single frame (look at the stars and the detail in the nebula).

    Have I noticed anything good about stacking? Yes! When I use high ISO, for example 1600 or 3200 stacking does a good job of suppressing the noise. At 800 however there is so little noise one light pass through noise removal software (which all the above processed images had done) fixes it.

    So I know it has to be me, there is no way everyone on the internet using all this software is wrong, so what am I doing wrong or what am I missing? Feel free to call me an idiot or whatever so long as you point me in the right direction.

    Allan

    PS. If anyone is interested and wanted to, PM me with your mailing address and I will burn all the originals (in TIFs) to CD and mail them to you to play with.

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  3. #2
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    I'll have a go at stacking these images. Can you put them in dropbox public folder and then post the links on here (right click and copy URL).

    Or put them in a folder in the non public part of dropbox and use my E mail to share the folder (I'll PM you with my E Mail address). I'll let you know all the DSS settings I use). Please put the darks, flats and Bias in sub folders.

    In case you are not familiar with Dropbox, it is a free download which is very useful for sharing large files.

    Thanks
    Carole

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    PS: Just noticed you have a Nikon camera.
    Nikon D7000 imaging camera,
    I was reading an article recently that says Nixon does something to the RAW files and converts them to a different format which ruins some of the RAW data.

    I don't know whether this could have something to do with it.

    Carole

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  7. #4
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    Quote Originally Posted by carastro View Post
    PS: Just noticed you have a Nikon camera.

    I was reading an article recently that says Nixon does something to the RAW files and converts them to a different format which ruins some of the RAW data.

    I don't know whether this could have something to do with it.

    Carole
    I could be very wrong but I would think that if I get a single light frame that I can turn into a good image, that 30 lights, 15 darks, 15 bias and 15 flats from the same camera that produced a good single light image should be better, no?

    Allan

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  9. #5
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    Yes that would seem logical.
    Let's hope it's something in the DSS stacking procedure we can iron out.

    I had a problem once with getting holes inthe stars once I had stretched the image when I did it on my laptop yet when I stretched the same data on my desktop there were no holes. It turned out to be something in my DSS settings on my laptop.

    I've got the files, but they will take some time to download.

    Carole

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    Thanks, I will be really interested in seeing your results.

    Allan

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    Well I have stacked the image in DSS and it looks OK to me. There is something strange going on with some of the brighter stars which I can't explain but this is on some of Allan's images as well.

    I have to say though that the final stack in DSS was a lot paler than I have been used to seeing and I had to adjust the Luminance tabs so that they were all reasonably central to get some sort of reasonable colour, something which I don't normally touch.

    This is the final stacked image before adjustment.

    I have temporarily downloaded them from my website as I can't get the thumbnails to open (a frequent occurence).

    Attached Images Attached Images
    Last edited by carastro; 10-31-2011 at 06:05 PM. Reason: Thumbnails don't open.

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    This is while the "apply" is being made after luminance adjustment.

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    I did One iteration of levels bringing the left slider towards the histogram.

    Two iterations of curves, anchoring the white and black points and lifting up the middle of the histogram where the nebulosity is situated.

    I then repeated this with the Blue channel and then the red channel.

    Finally I applied - filter/noise/despeckle 2 iterations as it was a bit noisy.



    Close up of the middle section (it is very very slightly out of focus, but some good data there):



    Allan, If you want to send me your E mail address I'll give you all the DSS settings I used, then you can check them against your settings.

    Carole

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    Carole, take one of the light frames and the stacked frames, edit them both about the same and then look at the stars and detail in the nebula. Do you see an improvement with the stacked image? If so, what is better?

    When I do that the stars are sharper and there is quite a bit more detail in the nebula in the single image as compared to the stacked image. That is what puzzles me.

    Allan

    PS. Thanks again for trying this experiment!

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