Hello Elle,
There has been a lot of discussion about this subject and what ICC says is: - Media white point tag is intended to store the chromacity of media, i.e, the measured white of unprinted paper. - On monitor profiles, chromacity of media is always D50, independently of screen white. Note that PCS is modeled as a reflection print, and in this case is a perfect diffuser. If you illuminate the media with light other than D50, then you have to convert to D50 by means of chromatic adaptation and store it in the CHAD tag. For monitor profiles, this illuminant is the screen white point. This is valid for both V2 and V4, but some V2 makers did a misinterpretation of the spec. This includes AdobeRGB1998.icc and sRGB Color Space Profile.icm Updated profiles with fixed white point can be found in the ICC site. Additionally, most CMM hot-fixes this when such profiles are detected (lcms, for example) Otherwise this only affect to absolute colorimetric intent, which is seldom used. Regards Marti Quoting Elle Stone <ellest...@ninedegreesbelow.com>: > How should the following two quotes from the V2 version of the ICC > specifications that is linked to on the color.org specifications page > (http://color.org/icc_specs2.xalter) be interpreted? > > 6.4.25 mediaWhitePointTag > Tag Type: XYZType > Tag Signature: ‘wtpt’ (77747074h) > This tag specifies the media white point and is used for generating > ICC-absolute colorimetric intent. See Annex A for a more complete > description of its use. > > A.3.1.1 MediaWhitePoint Tag > The mediaWhitePointTag contains CIE 1931 XYZ colorimetry of the white > point of the actual medium. If the viewer completely adapts to the white > point of the medium (as is often the case with monitors) this tag should > be set to Xi, Yi, Zi (the PCS white point). If chromatic adaptation is > being applied to the PCS val-ues, the adaptation should be applied to > the mediaWhitePointTag values as well. > > > My understanding of V2 ICC profiles is that there are two ways to > specify a V2 ICC profile's source white point: > 1. You can either put the source white point in the media white point > tag (for example D65 for sRGB). > 2. Or you can put the ICC D50 illuminant values in the media white point > tag and include a chad tag that gives the chromatic adaptation matrix > from the source white point to the ICC D50 illuminant. > > > An alternative interpretation of the quote from Annex A is that for at > least some ICC profiles, perhaps including the D65 sRGB profile, the > media white point tag should *always* read D50 even for V2 sRGB profiles. > > Does the quote from Annex A: > > 1. Apply specifically to sRGB, because sRGB is (sometimes) used as a > monitor profile? And if the quote does apply to sRGB, does this mean > that V2 sRGB profiles that have the sRGB D65 XYZ values in the media > white point tag actually violate the (or perhaps some particular version > of the) V2 ICC specifications? > > 2. Apply to *any* ICC profile that has 'mntr' in the header, which would > include AdobeRGB1998 and ProPhotoRGB? > > 3. Apply only to the particular device ICC profile that is being used as > the display device profile in a particular color-managed workflow? > > 4. Some other case? > > In whatever cases where the quote from Annex A might apply, is it > suggestive (can be done, but not mandated) or normative (must be done or > else the profile violates the V2 ICC specifications)? > > Thanking you in advance for any enlightenment on this topic. > > Elle Stone > > ------------------------------------------------------------------------------ > Android apps run on BlackBerry 10 > Introducing the new BlackBerry 10.2.1 Runtime for Android apps. > Now with support for Jelly Bean, Bluetooth, Mapview and more. > Get your Android app in front of a whole new audience. Start now. > http://pubads.g.doubleclick.net/gampad/clk?id=124407151&iu=/4140/ostg.clktrk > _______________________________________________ > Lcms-user mailing list > Lcms-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/lcms-user ------------------------------------------------------------------------------ Android apps run on BlackBerry 10 Introducing the new BlackBerry 10.2.1 Runtime for Android apps. Now with support for Jelly Bean, Bluetooth, Mapview and more. Get your Android app in front of a whole new audience. Start now. http://pubads.g.doubleclick.net/gampad/clk?id=124407151&iu=/4140/ostg.clktrk _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
