"blend RGB colors using gamma" buggy? When to use it?

FD
Posted By
false_dmitrii
Jul 28, 2006
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1176
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0
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Closed
When is it useful to enable "blend RGB colors using gamma" in Color Settings? The help text seems to suggest that enabling it at gamma 1 is "more accurate" than leaving it off, which makes me think the only reason to disable the checkbox would be for compatibility with other graphics software.

However, enabling gamma 1 blending sometimes causes very strange effects. For instance, if I use spot healing on very dark shadow areas of an image with an Epson 4870 profile, then apply a curves layer, the corrected areas become much lighter along the edges than they ought to be. This is especially prominent when the correction is performed on a blank raster layer, for the entire circle of the brush impression lightens evenly from the center all the way out to the 0-hardness edges. Turning off gamma 1 blending in this case returns everything to normal.

I think I saw something similar when I first installed PSCS2. I was using curves layers to adjust a near-black scan of a nighttime film shot, probably with a Minolta scanner profile applied. If I remember correctly, the dark sky became unusually bright with gamma 1 blending enabled; it didn’t look right until I switched the blend mode off. I’m not 100% sure of this, but before testing it again I’ll wait for feedback on my original question of when and why to use gamma 1 blending.

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