[Lcms-user] Missing PCS black point adjustment for perceptual transforms between version-2 and version-4 profiles (and vice versa)?

[Maurice L. <mau...@gm...>]

Hi,

I've been looking through the internals of LCMS2, in particular function
DefaultICCintents() which converts the array of profiles, intents etc. into
a cmsPipeline.

But I'm a bit puzzled, since I would expect to see a conversion being
introduced in case of a transformation with a perceptual rendering intent
between a version-2 profile and a version-4 profile (or vice versa) in
order to handle the difference in PCS black points of version-2 and
version-4 profiles.

In order to verify this, I did a test with a floating point conversion of
RGB (0, 0, 0) from the version-4 sRGB_v4_ICC_preference.icc profile to the
version-2 sRGB2014.icc profile (and I multiplied the output values by 255).

If everything is fine, I would expect the result to also have RGB = (0, 0,
0).
If there is a black point mismatch, I would expect the RGB value to
correspond to the version-4 black point (which has a lightness of about
3.1).
The resulting RGB value (times 255) that I got was (11.311, 11.311,
11.311), which indeed corresponds to the lightness of the version-4 PCS
black point.

This suggests that adjustments between the version-2 and version-4
perceptual PCS black points (and vice versa) are indeed missing.
Or am I misunderstanding something?

With kind regards,
Maurice