If I create a gray picture (RGB, doesn't matter if it is 8bit or 16bit), then convert it to Lab 16bit and then back to RGB it is not neutral gray any more. Shouldn't it stay neutral gray ? Also when I create a neutral gray RGB picture and add a working layer (for example gaussian blur, but it happens with others also) and set it to work on L channel of Lab only, and set the strength to 500% (radius doesn't matter) then the picture goes very blue. Same problem ?
Best wishes
procyon
Lab conversion
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Hoogo
- Betatester
- Beiträge: 4031
- Registriert: So 03 Jul 2005 13:35
- Wohnort: Mülheim/Ruhr
Re: Lab conversion
I don't know the reasons... 
Conversions from/to Lab need a profile or at least a white-point and quite some calculations, so I can accept slight rounding errors. A quick check showed me a difference of max. 2 values summed up.
And for the 2nd effect I can think of a different calculation, whether it is done in "real" Lab or in RGB. A better test pattern for that effect with big blotches of red ff0000 and green 00ff00 on it. When you apply your 500%-blur on a RGB-picture but choose Lab in the filter, the transition turns white. If the picture is Lab, too, the tansitions are colorful. That might even depend on the OS, but I'm not sure.
Conversions from/to Lab need a profile or at least a white-point and quite some calculations, so I can accept slight rounding errors. A quick check showed me a difference of max. 2 values summed up.
And for the 2nd effect I can think of a different calculation, whether it is done in "real" Lab or in RGB. A better test pattern for that effect with big blotches of red ff0000 and green 00ff00 on it. When you apply your 500%-blur on a RGB-picture but choose Lab in the filter, the transition turns white. If the picture is Lab, too, the tansitions are colorful. That might even depend on the OS, but I'm not sure.