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  1. #1
    Senior Member

    Startrails post-processing in Darktable

    Startrails post-processing in Darktable
    Hi,

    I spent 3 hours in the mid of a chilly night and then mistakenly set iso=800 and 30min to shot a startrails image (extremely over-exposed, see pic1). Then I used darktable to reduce the exposure to make it visible (as in pic2). I just wonder if I can continue with darktable to bring the dark sky at corners to the big central part of the still over-exposed area? (so to show startrails there) Appreciate any help and advice.

    Startrails post-processing in Darktable-2020-04-28-23.27.35-s.jpeg

    Startrails post-processing in Darktable-2020-04-28-23.27.35-exp-s.jpeg


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  2. #2
    Senior Member
    Needa's Avatar

    Re: Startrails post-processing in Darktable

    Don't think it is going to work. Looks like there is no detail in the center.

  3. #3
    Senior Member

    Re: Startrails post-processing in Darktable

    Hi Needa, Thanks for responding.

    I think in the center there are still star trails just kind of washed out by extreme over-exposure even though I have reduced exposure level to the lowest limit... am thinking is it possible to start with the 2nd pic as exposure at 0 EV and draw a circular mask (covering central part) and reduce exposure only in the mask? I am a new user of Darktable and need a lot help in basics. Thanks

  4. #4
    Senior Member
    Needa's Avatar

    Darktable and need a lot help!

    Me too!

    I don't think you are going to be able to resurrect it, way over exposed. See the color change in the center. What does it look like on the back of the camera.
    But if you want to try here are some thoughts.
    First duplicate the image several times, so you can see how different versions come out.
    No need to start with the new picture you can stack a second instance of exposure on the image you are working with.
    Try global tonemap instead of exposure. Move the target slider to the left.

    Good luck! Let me know how it works out.
    Last edited by Needa; 04-30-2020 at 12:30 PM.

  5. #5
    Senior Member

    Re: Startrails post-processing in Darktable

    Startrails post-processing in Darktable
    Thanks, Needa.

    I tried a new exposure instance and a tonemapping. The outcome looks better but the improvement still unsatisfactory. Guess like you said it's gone for now... until next experiment.

    Startrails post-processing in Darktable-2020-04-28-23.27.35_01-exp-s.jpeg

  6. #6
    Senior Member
    Needa's Avatar

    Re: Startrails post-processing in Darktable

    Quote Originally Posted by blackstar View Post
    Thanks, Needa.

    I tried a new exposure instance and a tonemapping. The outcome looks better but the improvement still unsatisfactory. Guess like you said it's gone for now... until next experiment.
    blackstar

    Was looking for something I read about 3 ways to try to recover over exposed image in Darktable ran across this, thought you might find it of interest.
    https://www.darktable.org/tag/overexposed/

  7. #7
    Senior Member

    Re: Startrails post-processing in Darktable

    Thanks, Needa.

    It looks promising enough for trying and using. I'll post back afterward.

  8. #8
    Senior Member

    Re: Startrails post-processing in Darktable

    Startrails post-processing in Darktable
    Needa,

    I tried some re-processing: 2 more instances of reducing exposure -- until everything is dark; "Color reconstruction" as the article recommends -- with little effect; "Highlight reconstruction" (also mentioned in the article, but not the primary option) -- with "Reconstructing in CL", suddenly and surprisingly star trails begin to come out from the dark sky! (though some bright, some faint due to focus issue)

    So this is! Thank you for letting me know the article and I learned.
    Startrails post-processing in Darktable-2020-04-28-23.27.35_02-exp-s.jpeg

  9. #9
    Senior Member
    Needa's Avatar

    Re: Startrails post-processing in Darktable

    That is impressive all thing considered. Just bookmarked the page for myself.

  10. #10
    Senior Member

    Re: Startrails post-processing in Darktable

    Hi Needa,

    Thanks for the encouragement. I think it can still be further improved contrast-wise though not my original intention. I'll try again later when the moon is gone and make sure to get iso and focus right.





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