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: MARK SEGAL <email@hidden>
- Date: Tue, 9 Jun 2009 09:08:13 -0700 (PDT)
Marco,
This is really very clearly and correctly explained here in the "King's English". It's a pleasure to see such succinct, informative contributions.
Mark
________________________________
From: Marco Ugolini <email@hidden>
To: ColorSync Forum <email@hidden>
Sent: Tuesday, June 9, 2009 12:00:36 PM
Subject: Re: BCP or no BCP to epson without rip
Augusto wrote:
>Printing to Epson is probably the most popular way for photographers to
>squeeze the best of their pictures to paper and although I have been using
>this workflow for some time I still find contradictory opinions on this BPC
>matter.
>
>With a relative colorimetric intent, there is a more unanimous acceptance
>that BPC "on" is the way to go and even the recommended intent if the image
>gamut fits in the destination profile gamut.
>
>With perceptual, I am confronted with a more ambiguous knowledge. I find
>very respected people recommending their profiles to be used with BPC "off"
>and no less respected people saying that BPC should always be "on" with
>profile conversion cause even if it does no good it will not harm.
>
>I would like to "nail" ( if possible) once for all, this workflow and I
>would very much appreciate your knowledge on this question.
Augusto,
This is how the theory goes:
A Relative Colorimetric transform will always map the white of the source color space to the white of the destination space. Without BPC (Black Point Compensation), the black of the source is mapped to a colorimetrically equivalent black in the destination. In other words, if the deepest black in the source is *lighter* than the deepest black in the destination, it will be mapped to a a tone that is lighter than the darkest tone achievable in the target color space, and the print will appear "washed out" to some degree, meaning less contrasty than it could be otherwise. If the source's darkest black is *darker* than the darkest black in the destination, a more or less large portion of the source's shadow detail will be *clipped*. In other words, there will occur some loss of detail in the shadows.
To sum it up, BPC will map the source's blacks to the destination's blacks, no matter whether the source's blacks are lighter or darker. In either case, the resulting transform will produce the deepest possible blacks in the destination, and also preserve shadow detail (without clipping).
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.
Marco Ugolini
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