Re: [Lcms-user] Re: Thank You

[<ma...@li...>]

Hi,

>This sounds exactly what I want, the source of my confusion seems to
>be Adobe - Here's what it says in the Color Settings dialog re
>Absolute Colorimetric in Photoshop 7:
>
>Absolute Colorimetric: Attempts to match the absolute Lab coordinates
>of the destination colors to the absolute Lab coordinates of the
>source colors. Does not adjust for the different media white points.
>Mostly used for "logo" colors, and for hard proofing. Not recommended
>for most color conversions.

This is correct. I assume they refer "absolute Lab" as D50-based Lab.
Otherwise, in this particular case, XYZ does make perhaps more sense,
since Lab is usually white point independent.

> The "not adjusting to media white points" seems to be what I don't want.

Then you can use relative-colorimetric intent. Is is supposed to be equal to
absolute colorimetric except it also translates white point.

ICC architecture and PCS is based on this "white point independence". In fact,
absolute intents are hard to implement. There is a chromatic adaptation
embedded into profiles to remove these casts. The CMM must somehow
"undo" this chromatic adaptation to get good abs. colorimetric intent. The last
version of lcms does that, as well as Adobe ACE. Is quite curious to see that
Windows ICM doesn't apply these necessary corrections....

Cheers
Marti.


----- Original Message -----
From: "James Burgess" <jr...@pi...>
To: "Martí Maria" <ma...@li...>
Cc: <lcm...@li...>
Sent: Wednesday, July 24, 2002 2:11 PM
Subject: Re: [Lcms-user] Re: Thank You


At 10:37 AM -0320 7/24/02, Martí Maria wrote:
>So, if your embedded profile says "this image is using D65" and
>the monitor profile says "this monitor is using D93", a transform
>using perceptual,  saturation or relative intents will ignore this
>information, and a transform using absolute colorimetric one will
>convert RGB of 255 255 255 to D65 and then will represent D65
>chromaticity in the monitor. This is quite yellow under D93 illuminant.
>
>Regards,
>Marti.

This sounds exactly what I want, the source of my confusion seems to
be Adobe - Here's what it says in the Color Settings dialog re
Absolute Colorimetric in Photoshop 7:

Absolute Colorimetric: Attempts to match the absolute Lab coordinates
of the destination colors to the absolute Lab coordinates of the
source colors. Does not adjust for the different media white points.
Mostly used for "logo" colors, and for hard proofing. Not recommended
for most color conversions.


The "not adjusting to media white points" seems to be what I don't want.