QTR-Quadtone RIP

Hello Roy,

I hope you don't mind me saying so, but if I have analyzed things
correctly, the ICC profiles created by create-ICC have some anomalies
of their own. Maybe this accounts for some of the observed behavior.

ICC output profiles contain 6 tables: perceptual, relative
colorimetric and saturation intents, each in both directions. I'll
ignore the saturation intent tables because they have little to do
with photography. In the profiles constructed by create-ICC, the BtoA0
(perceptual Lab to printer) and AtoB1 (colorimetric printer to Lab)
tables are correct. These are the tables used for printing and soft
proofing in perceptual mode. However, their inverse tables (AtoB0 and
BtoA0) are *not* the inverse, but rather a copy of the same table in
the other mode: AtoB0 is a copy of AtoB1 and BtoA0 is a copy of BtoA1.

This breaks the use of the absolute and relative colorimetric
rendering intents. In addition, it makes it impossible to convert
*back* from the ICC profile space without affecting the look of the
image, because the inverse tables are not really inverse tables. The
QTR-Create-ICC-RGB-bpc application fixes the AtoB0 table (making an
invertible perceptual mapping), but changes the (correct) AtoB1 table,
thereby breaking soft proofing.

For more info, see the following post that I have written a little
over a month ago:
http://tech.groups.yahoo.com/group/QuadtoneRIP/message/7113

I think that the create-ICC application should be updated to create
AtoB0 and BtoA1 tables that are true inverse mappings of the BtoA0 and
AtoB1 tables, respectively. This would enable the use of the absolute
and relative colorimetric intents and my guess is that it would also
obviate the need for the separate create-ICC-RGB-bpc application.

Best Regards,
Simon


--- In QuadtoneRIP@yahoogroups.com, "Roy Harrington" <roy@...> wrote:
>
> Hi Peter,
> 
> There are 3 create icc programs because some editing programs have
> restrictions and anomolies.
> 
> QTR-Create-ICC makes a grayscale ICC for printing and softproofing.
> Photoshop handles these and works great.
> 
> QTR-Create-ICC-RGB makes a functionally identical ICC but it's in
RGB format.
> Programs such as Lightroom, Qimage, and I think others don't work in
> grayscale so you need an RGB format ICC file.
> 
> QTR-Create-ICC-RGB-bpc is similar to the above but maps black-to-black
> directly.  This takes away softproofing with simulate-ink-black
capability.
> But some programs seem to get the "Black Point Compensation" wrong with
> the above ICC profiles so this ensures that everything is correct.
> 
> It's unfortunate that there seems to be variation of how different
programs
> handle B&W issue but that is the current state of things -- so
different ICCs
> are needed for them.
> 
> Roy
> 
>