QTR-Quadtone RIP

CLARIFICATIONS:

*  All conversions were perceptual (but see below).  CM_OFF was done
in PS.  Others were done in Qimage.
*  All conversions were to my newly created custom RGB profile.
*  Ernst's point about the PS CM never being fully off is well taken,
but these are large changes.  All programs than can display the
histogram (e.g.  BreezeBrowser Pro), display the same dMax loss.
*  I was using Qimage 2008.104 but have since upgraded to .109 (latest
- see below).
*  I tested Ernst's idea of using 8-bit input to Qimage to no avail -
same problem.
*  Since the initial QTR-related problems with the CMS in Qimage were
discovered in early 2006, I have generally followed Ernst's workflow:
 i.e. create a copy and do the CM in PS, and do all other printing
manipulations in Qimage with CM off.  But this partly defeats one
purpose in using Qimage, the ability to print from master files and
not have to create special versions just for printing.  It works for
colour, but not it seems for B&W.

FURTHER RESULTS

I upgraded to 2008.109 and one histogram changed.  The one with
profile conversion done in Qimage but no BPC ("CM On, BPC off in Q")
now looks exactly the same as the one done in Qimage *with* BPC ("CM
on, BPC on in Q").  Now in both cases the black point shifts from 1 to
27 with an associated loss in dMax.

This tests my sanity.  I am fairly sure that I used all perceptual
conversion when I produced those histograms.  But I can't now
replicate the middle histogram ("CM On, BPC off in Q") using *any* of
CM options in Qimage.  This suggests that something has change in
Qimage, but the revision log says nothing about any changes to the CM.

I decided to push the tests a step further.  I also produced
histograms for conversions in Qimage to generic profiles.  Results are at:

  http://www.ferdinand-paris.com/BPC-Qimage_V2.png

CONCLUSIONS

*  BPC is not the problem per se when I convert to a QTR custom
profile, the reading of the custom profile by the whole Qimage CMS is.
*  There is something about the custom profiles that Qimage can't
handle, but can with the generic profiles.  I don't know if this has
been discovered and commented on before.

@Roy:  I still don't understand the differing treatment of BPC between
custom profiles and the generic profiles that you mentioned in post
5728.  What practical difference would I expect to see (other than the
fairly obvious ones in Qimage)?

F_P