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Basic GIMP 2.9 Guide for quick Astro photo editing

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#1 Foobaria

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Posted 03 February 2018 - 05:02 PM

Found the following by accident, but you can quickly make great results in Gimp 2.9 (a free program) to put the final touches on your stacked astrophoto.   Even a very faint object can look great with this method.

 

  1. First, output your astro photo from your Stacker program (like DSS) to a TIFF file ( i use an OSC, just one full-color file).  So, Stack your multiple shots before doing the following.
  2. Open the output/stacked file with Gimp 2.9 or  later (2.8 won't open that kind of TIFF)
  3. Choose Colors 
  4. Choose Levels (not Curves) -- this method is quicker and easier than the Curves method
  5. You are on the "Adjust Color Levels" pop-up screen.
  6. Look under where it says "All Channels" on this pop-up screen. 
  7. Push  the "Auto Input Levels" button from the middle of this pop-up screen titled "Adjust Color Levels".  This will make an immediate improvement to your image -- its like a little bit of magic.   But you can do a little more.
  8. Look to the right of this button, you'll see 3 droppers, one black, one gray, one white.   Choose the black dropper. 
  9. Then move this dropper into the area that's supposed to be black say outside of your central/object of attention AND click.  This makes what's supposed to be black actually black.  You can do it more than once if needed in different areas that are supposed to be black. 
  10. Then if you want to enhance further you can try this (optional, only if you like the result):
  11.      Under the Input Levels (at the top of the pop-up), pull the white triangle from the far right, pull it left, until your image is further enhanced (skip this if you don't like it). 

Then output your result as a png:

  1. Select File,
  2. Export As
  3. Give it a file name with .png (or .jpg) extension 
  4. Push Export.  (your original TIFF is still safe/ unedited) 

 

I've attached screen-prints (not actual original files) of the before / after of the Horsehead nebula region.

Attached Thumbnails

  • before.PNG
  • after.PNG

Edited by Foobaria, 03 February 2018 - 06:28 PM.

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#2 hoop

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Posted 24 March 2019 - 08:48 AM

I tried this with Gimp 2.10 and I'm quite pleased with the results. I am just getting into AP and I was getting a bit frustrated with processing my images until now.

#3 Old star gazer

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Posted 21 July 2019 - 04:12 PM

I can't say I'm getting the dramatic change in the image that you are getting here. If I understand correctly, you are taking a .tiff file directly from Deepskystacker and doing just this little bit in Gimp and you get that much detail? Are you leaving out any part of the process?



#4 iborg

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Posted 01 September 2019 - 11:30 PM

Hi Sputinik

 

It took some shots of M8 last Friday, by chance, I followed the method above, and yes! I did get that dramatic a difference in the image on screen.

 

It still looked rubbish mind you, but, that is because I don't have enough data to actually get a good image out.  I am working on getting something better, but, really need to go back and get more stills.

 

Philip



#5 Bart Declercq

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Posted 02 September 2019 - 03:18 PM

I can't say I'm getting the dramatic change in the image that you are getting here. If I understand correctly, you are taking a .tiff file directly from Deepskystacker and doing just this little bit in Gimp and you get that much detail? Are you leaving out any part of the process?

The image on the left is "linear" (as in : the pixel values represent the recorded brightnesses exactly) - since the horsehead nebula is much, much fainter than the stars in the image, a linear stretch can't show both the stars and the nebula nicely - for that you need to make the brightness curve non-linear.

 

In linear stretch, something that is twice as bright has double the pixel value

in non-linear stretch, you can do things like "something that is ten times as bright has double the pixel value" or even more flexible brightness curves.

 

This allows you to set the stretch so the faint nebula is only a little bit fainter on screen than the bright stars, which is precisely what's happening between both images.

 

Non-linear stretching in one form or another is virtually essential in astrophotography, since most objects have both very faint and very bright parts.


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#6 VincentAnthony

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Posted 20 September 2020 - 02:46 PM

Thank you for sharing this explanation; this really is helpful.
I would like to ask someone how to combine l, r, g, & b photos in Gimp? 

This is my very first time processing astrophotography and I have multiple luminance, reds, greens, and blues. After I stack the frames into four separate files, how do I combine them into a full-color image using Gimp?


Edited by VincentAnthony, 20 September 2020 - 02:48 PM.


#7 decep

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Posted 20 September 2020 - 07:21 PM

Thank you for sharing this explanation; this really is helpful.
I would like to ask someone how to combine l, r, g, & b photos in Gimp? 

This is my very first time processing astrophotography and I have multiple luminance, reds, greens, and blues. After I stack the frames into four separate files, how do I combine them into a full-color image using Gimp?

Just go to Youtube and search "gimp lrgb" and you should find plenty of resources.

 

I used this one to get a primer for combining LRGB images:  https://www.youtube....h?v=UbUUEahiFJY


Edited by decep, 20 September 2020 - 07:21 PM.


#8 VincentAnthony

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Posted 21 September 2020 - 03:56 PM

Just go to Youtube and search "gimp lrgb" and you should find plenty of resources.

 

I used this one to get a primer for combining LRGB images:  https://www.youtube....h?v=UbUUEahiFJY

Thank you for the link.
Do you know if it's possible to fix bad columns in Gimp?



#9 decep

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Posted 21 September 2020 - 04:19 PM

Thank you for the link.
Do you know if it's possible to fix bad columns in Gimp?

Your strategy for fixing bad columns probably depends on how big the columns are and how "bad" they are.  The most common fix is just using dark calibration frames to eliminate the bad columns in your stacking phase.


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