QTR-Quadtone RIP

mchaney1234567890 wrote:
> As Roy indicated, BPC is not part of the ICC spec at all: it is an
> Adobe abomination, one of which (as is often the case with Adobe) is
> not completely specified for third parties to be able to reproduce. 
> There are additional limitations with BPC for ICC v4 profiles as BPC
> really makes no sense for perceptual intent in v4 profiles. 
> Perceptual intent for v4 profiles runs on its own PCS and is
> inherently different than RC and other intents making BPC undefinable
> by the spec.  There are other issues as well, for example, when a
> profile uses a black point tag and that tag doesn't agree with the
> data in the look up tables.  On top of that is the fact that black
> point for perceptual intent in v4 profiles should be a fixed value. 
> There's also color "noise" to deal with and the fact that you have to
> deal with near-black.  All software will handle that a bit
> differently.  When using v4 profiles, many times the profiles
> themselves are not truly v4 as I've seen many that are a mix between
> v2 and v4 and don't have all the required v4 tags.  Hard to tell which
> of these factors is causing the problem, but I've been over BPC with
> Marti Maria many times and am satisfied that it is working properly in
> Qimage/LCMS.  PhotoShop also tends to "prune" profiles and do things
> without telling you so in cases like this, the answer could be as
> simple as PhotoShop ignoring BPC under these conditions while Qimage
> still tries to do something with it.  Maybe the best thing in cases
> like this is to turn off BPC when using perceptual intent with v4
> profiles as BPC really makes no sense in those cases anyway.
> 
> Mike

Mike,

I see differences between BPC on and off with Photoshop on 
the same profile. It has taken too much time again so I'm 
not going to press this thing more. Better see whether I can 
change the profile data a bit to get the same effect with 
BPC off in Qimage.

Is there any chance that similar Perceptual Rendering + BPC 
problems happen with color printing + color profiles on 
gloss = high Dmax. ?  Profiles like delivered with the HP 
Z3100 or custom profiles from Colorvision/Pantone 
ProfilerPro, Monaco Profiler, etc ?  Reading back in the 
Qimage mailing list your advice has been to keep BPC on with 
Perceptual Rendering (where it shouldn't add and do no harm 
either) and keep it on with Relative Colormetric where it suits.


Met vriendelijke groeten,  Ernst


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