Rendering intents relative colorimetric and perceptual produce identical files
Under some conditions, there's no difference between relative colorimetric and perceptual rendering intents, even though out-of-gamut colours are present.
http://tech.kovacs-telekes.org/files/dt2-rc3-rendering/ contains a raw file and different exported versions; the corresponding 'relative colorimetric' and 'perceptual' rendering intent pairs (DSC_9526-nolcms2-sRGBwebSafe-perceptual.jpg and DSC_9526-nolcms2-sRGBwebSafe-relative.jpg; DSC_9526-withlcms2-sRGBwebSafe-perceptual.jpg and DSC_9526-withlcms2-sRGBwebSafe-relative.jpg) are binary equal if we ignore the exif header.
I exported 3 versions of the provided photo (each version has a different set of operations applied). I tried all combinations:
LCMS2 on vs off
web-safe vs black_scaled
perceptual vs relative
So I ended up with 24 output files. I found that the 'perceptual' and 'relative' files were the same size; they looked the same in Geeqie (colour management turned on, display profile loaded); and after using
"exiv2 rm *jpg" to delete all metadata, the pair of images was binary equal.
I'd think this sounds like a bug, but I do admit I know very little about colour management.
Note that the results were different if I applied a v4 profile sRGB_v4_ICC_preference.icc from http://www.color.org/srgbprofiles.xalter: DSC_9526-withlcms2-sRGBv4-perceptual.jpg is visually identical (for me) with DSC_9526-nolcms2-sRGBv4-perceptual.jpg and DSC_9526-nolcms2-sRGBwebSafe-relative.jpg with DSC_9526-withlcms2-sRGBwebSafe-relative.jpg, but members of the relative/perceptual pairs are distinct.