+- Gimp-Forum.net (https://www.gimp-forum.net)
+-- Forum: GIMP (https://www.gimp-forum.net/Forum-GIMP)
+--- Forum: General questions (https://www.gimp-forum.net/Forum-General-questions)
+--- Thread: RGB to LCH Conversions (/Thread-RGB-to-LCH-Conversions)
RGB to LCH Conversions - NotEvenStickMen - 04-11-2023
I've coded a conversion of RGB to LCH & tried to use Gimp to verify my numbers. However, there are discrepencies which I don't understand.
e.g.
#0009be RGB(0,9,190): Gimp LCH (21.3, 102.9, 300.7) My LCH (23.4, 105.1, 305.7)
The ColorMath Online Colour converter & Converting Colours Converter agree with me, give or take some minor rounding errors.
Is Gimp doing some sort of Out of Gamut compensation? (I'm guessing at this because I'm a beginner in this area).
RE: RGB to LCH Conversions - Ofnuts - 04-11-2023
Do you convert from RGB directly, or do you take in account gamma correction, and if so, how?
RE: RGB to LCH Conversions - NotEvenStickMen - 04-11-2023
I'm using sRGB values as input which is already 2.2 isn't it? I'm on a v steep learning curve here so it's v likely that I've missed something.
(sRGB -> XYZ -> LAB -> LCh using D65 white point)
RE: RGB to LCH Conversions - Ofnuts - 04-11-2023
Your values agree with this.
Yes, gamma is 2.2 although technically it is linear (=0) for very small values but I don't think this matters here.
The answer is likely in the source code of the GEGL component of Gimp.
RE: RGB to LCH Conversions - NotEvenStickMen - 04-11-2023
Given 3 other converters agree with me, I think I'm happy to go with what I've got for my purposes (though we could all be creating the same error based on internet searches :-)).
Would you recommend that I progress this e.g. with a bug report, in case there's an issue within Gimp?
RE: RGB to LCH Conversions - Ofnuts - 04-11-2023
(04-11-2023, 06:34 PM)NotEvenStickMen Wrote: Given 3 other converters agree with me, I think I'm happy to go with what I've got for my purposes (though we could all be creating the same error based on internet searches :-)).
Would you recommend that I progress this e.g. with a bug report, in case there's an issue within Gimp?
Well, at least you could get an answer about the difference.
RE: RGB to LCH Conversions - NotEvenStickMen - 04-11-2023
Thanks for your replies; much appreciated.