[argyllcms] Re: Some question about chromatic adaptation in color management
- From: Chris Lilley <chris@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 25 May 2012 21:56:11 +0200
On Friday, May 25, 2012, 9:42:33 PM, Ivan wrote:
IT> 1. How color managed software visualize images on characterised
IT> monitor: program just make matrix calculation between source and
IT> destination (monitor) profiles? Or additionally it calculate
IT> chromatic adaptation shift according to monitor white point? It
IT> seems that make, because white pixels of image is visualised as
IT> full white of monitor, and without correction according to actual
IT> display white point image will be look not as expected.
IT> Or color management logic conciser that user adopted to D50
IT> illuminant not to display white point?
If the source profile does not have a D50 whitepoit then the image data goes
through a chromatic adaptation transform (CAT) to D50. And if the destination
profile does not have a D50 whitepoint then the it goes through a CAT to take
it to the destination profile, too.
IT> 2. What white point is used in prints color managing: naked paper
IT> XYZ values or XYZ of ideal reflecting diffuser under D50 illuminant?
Good question to which I don't know the answer, but would be interested to
know. (I *suspect* it is the paper white values).
IT> 3. Lab PCS in profiles is always D50 Lab even if device has not
IT> D50 white point?
Yes. The profile, in ICC v.4, includes a chromatic adapration table which is a
linear Bradford matrix.
IT> Values recalculated, in that case, to D50 Lab using Bradford
transformation?
Yes. And as mentioned above, with perhaps a second Bradford transform to the
destination profile whitepoint.
--
Chris Lilley Technical Director, Interaction Domain
W3C Graphics Activity Lead, Fonts Activity Lead
Co-Chair, W3C Hypertext CG
Member, CSS, WebFonts, SVG Working Groups
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