Marti Maria schrieb:
Hi Gerhard,
It's a bug. Fixed in CVS.
Marti,
thanks, "-p <xxx> -c2" seems to work now :-)
It was caused from a new feature introduced in 1.14. Some printer profiles are broken in a way Lab of (100, 0, 0)Though I find this workaround a useful feature :-) (I also have been bothered in the past by scum dots resulting from inaccuracies), I want to object, that it is also possible that a profile _wants_ to map PCS CIELAB=[100,0,0] to CMYK != [0,0,0,0] _intentionally_.
does not map exactly to unprinter paper. This is because the encoding of PCS makes extremly difficult to map white into an exact node, so, this was causing scum dot. lcms 1.14 fixes that by forcing exact white to white on all but absolute colorimetric intent, no matter what profile says.
(E.g. a proofing profile which emulates a different device, including the emulation of a different paper white, such that the device is _expected_ to lay down some ink for PCS white.)
Thus I'm wondering whether this workaround should be applied generally, or rather optionally, such that the user can turn it on or off?
Another possibility might be to apply the workaround only automatically, if there is "sufficient evidence", that CMYK != [0,0,0,0] for PCS white is caused by an inaccuracy, and not intentionally. For instance to apply the workaround only, if CMYK=[0,0,0,0], transformed to PCS, differs less than 1dE (or any other reasonable threshold) from [100,0,0]. For a profile, which intentionally maps PCS CIELAB = [100,0,0] to CMYK != [0,0,0,0], this strategy would limit the max. error possibly introduced by the workaround to 1dE (i.e. the selected threshold).
Regards, Gerhard
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