[Cin] gimp 2.10 and exact small color values

Andrew Randrianasulu randrianasulu at gmail.com
Tue Nov 7 20:10:50 CET 2023



So, forgetting about setting the FG color, *the way to create a surface
with a precision smaller than 1/256 in any component in GIMP 2.10 is using
the painting or color tools*.

You can do this, and use the color-picker tool to check for success:

   1. use at least 16bit precision
   2. fill an image with black;
   3. Set your foreground color to the lowest possible graylevel (010101
   hex color on the color dialog)
   4. use, for example, the bucket-fill tool and set the opacity to desired
   level (25% for 1/4 of 1/256 gray, (1/1024 gray)).
   5. Use the color picker tool to check if you got to the desired level
   (1/1024 gray will show 0.000076 for each component - while the 8 bit gray
   #010101 is 0.000304 for each component).
   6. Convert the image to "16 bit integer precision" back *before*
   exporting to .PNG file - I further tested and found out that attempts to
   save a 32bit FP precision image as a PNG file will result in an 8bit png
   file (all work above is lost). But if the image on GIMP is 16bit integer,
   then the PNG export generates a correct 16bit PNG. (Saving as native .xcf
   file format will preserve the precision, of course)


not sure if bug (IMO) in #6 was fixed or not ....

well, it seems back in 2019 trick was to use layer math, too ...

found via

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