Re: BCP or no BCP to epson without rip
Re: BCP or no BCP to epson without rip
- Subject: Re: BCP or no BCP to epson without rip
- From: Gerhard Fuernkranz <email@hidden>
- Date: Wed, 10 Jun 2009 22:29:55 +0200
Marco Ugolini wrote:
> As for the Perceptual rendering intent, it is supposed always to map source black to destination black. In that sense, BPC is redundant with Perceptual. But I have seen instances in which a poorly-built output profile will produce different results depending on whether or not BPC is activated -- though I have reason to believe that such behavior is anomalous, and that a properly-made output profile will always scale source black to destination black in the Perceptual rendering intent.
I fully agree that the perceptual rendering intent is basically supposed
always to map source black to destination black. The problem is the PCS
in between. In order that a perceptual transformation "source device
space -> PCS -> destination device" space can eventually map source
black to destination black, it is necessary that both, the source and
the destination profile have a common understanding to which PCS color
the device black point should be mapped. ICC V4 defines indeed a
reference medium for the PCS, with a well-defined black point, and the
perceptual tables in V4 profiles are expected to map between device
black and this well-defined reference medium black point in the PCS.
However, ICC V2 did neither define a reference medium nor a perceptual
black point for the PCS, giving the profile vendors basically the
freedom to map device black to whatever PCS color they like (for
instance, the perceptual intent of many V2 profiles seems to map device
black to PCS L*a*b* = [0,0,0], while some other V2 profiles map device
black to a color with L* > 0 in the PCS). Clearly, a perceptual
transformation between two profiles which assume different black points
in the PCS won't map source source black to destination black any more,
but BPC will still be required to align them. If both, source and
destination profiles are compliant V4 profiles, this should indeed no
longer be an issue.
Regards,
Gerhard
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