Marti, why a simple scaling is done? A chromatic adaptation could be executed instead? Giovanni Brembati
On Sat, 8 Sep 2007 11:38:42 +0200 "Marti Maria" <[EMAIL PROTECTED]> wrote: > > Hi, > > You are right; absolute colorimetric is not stored in >the profile. > Instead, BToA1 tag is used with a white point scaling. >The algorithm > is rather simple, it is performed on XYZ color space and >it is only > a plain scaling. > > AbsCol = RelCol * (MediaWhite / D50) > >For each of the tristimulous: > > Xabs = Xrel * (Xwtpt/0.9642) > Yabs = Yrel * (Ywtpt/1.0) > Zabs = Zrel * (Zwtpt/0.8249) > > Latest revision of ICC spec, however, specifies a DToB3 >tag, which stores > floating-point absolute colorimetric intent. But this is >an optional tag > and AFAIK very few CMM (if any) actually supports this >tag (lcms doesn't) > > > Hope this helps > > Marti Maria > The littleCMS project > www.littlecms.com > > > -----Original Message----- >From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On >Behalf Of John Weissberg > Sent: Friday, September 07, 2007 2:14 PM > To: lcms-user@lists.sourceforge.net > Subject: [Lcms-user] [Fwd: Using BtoA1 table with >rendering intent absolute] > > Consider the following case: Converting from Lab -> CMYK >using the BtoA > tables of an ICC profile with "Absolute Colorimetric" as >a rendering intent. > > As I understand it, the ICC profile does not contain an >Absolute > colorimetric BtoA table. Rather, it will use the >relative colorimetric > BtoA table, along with whitepoint data, for any look-ups >it makes. > > Can anyone explain what algorithm is used for these >conversions between > relative and absolute colorimetric? > > Is it simply adding/subtracting the DeltaE between the >whitepoint and > 100,0,0 ? Is this delta value added for all points in >the color space? > Only for points where L is above a certain limit? > > Any information is appreciated. > > > -- > John Weissberg > PerfectProof - Accuracy Made Easy > > www.perfectproof.com > www.printers-website.com > www.proofmaster.net > pakready.perfectproof.com > > USA > (888) 623 3662 Tel. > (888) 623 3662 FAX > > Europe > +32 15 272502 Tel. > +32 15 273740 FAX > > > -- > John Weissberg > PerfectProof - Accuracy Made Easy > > www.perfectproof.com > www.printers-website.com > www.proofmaster.net > pakready.perfectproof.com > > USA > (888) 623 3662 Tel. > (888) 623 3662 FAX > > Europe > +32 15 272502 Tel. > +32 15 273740 FAX > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. > Still grepping through log files to find problems? > Stop. > Now Search log events and configuration files using AJAX >and a browser. > Download your FREE copy of Splunk now >> > http://get.splunk.com/ > _______________________________________________ > Lcms-user mailing list > Lcms-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/lcms-user > > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2005. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Lcms-user mailing list > Lcms-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/lcms-user -------------------------------------------------------------------------- Questa estate, ovunque tu sia, per connetterti a internet componi con il tuo computer portatile il numero 7027010707 e naviga a tariffa urbana con una connessione dial-up veloce e affidabile. Registrati subito su www.infinito.it per ottenere i dati necessari per l'accesso. Infinito, l'accesso internet di qualità dal 1999. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
