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So I am editing a .png file from a website that I am working on. I downloaded the image (.png) and it has a yellow/green color in one of the objects. This color is important because it matches with the rest of the website's color scheme.

However, when I made my edits and saved as a new file, the green color was noticeably different.

I wondered if it was my fault on accident, so I opened the original file and saved it to a different name without editing or touching any part of the image. Yet still the color was noticeably different again.

    Original Color: rgb(141, 184, 73)
  Color After Save: rgb(127, 190, 65)

Is there any way to prevent this from happening in Gimp?

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Does your original PNG have any color management chunks (iCCP, gAMA, cHRM, and sRGB)? They might be getting lost during the conversion. If you have "pngcheck", use "pngcheck -v file.png" to find out. If not, "pngcrush -n -v file.png" or ImageMagick's "identify -verbose file.png" are other ways of listing the PNG chunks. –  Glenn Randers-Pehrson Aug 20 at 23:13
    
I am going to try that out right now. But as I do, is there anywhere I can go to and learn more about what png chunks are? –  Steven Rogers Aug 20 at 23:15
    
"No errors detected in [file].png (8 chunks, 88.9% compression)." I don't see anything wrong with this file, however I remember reading somewhere that gimp optimizes images for printing when it saves which is why I was led to believe it might be gimp's fault. I could very much be wrong on that part. –  Steven Rogers Aug 20 at 23:19
    
You have to use the "-v" option of pngcheck to see the chunk list. Run it against your original and your GIMP output. Links to the PNG specification may be found at libpng.org/pub/png/pngdocs.html –  Glenn Randers-Pehrson Aug 20 at 23:40

1 Answer 1

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This has to do with image color profiles - in GIMP, before opening your file for editing, go to edit->preferences, and in the Color Management page, set the File Open Behavior to Ask What To Do - then try different actions - one of which should preserve the numeric color values.

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