Am 19.02.2008 um 22:20 schrieb Chris Murphy:
On Feb 18, 2008, at 5:40 AM, Rolf Gierling wrote:
Hello Chris, Florian,
Am 18.02.2008 um 03:28 schrieb Chris Murphy:
<snip>
Also, the data does not actually get converted to the PCS, ever. The
PCS is just a means to an end. It allows a colorworld to be created
between a source and destination space. Image data is converted
directly from source to destination. It does not actually get passed
through LAB or XYZ as an intermediary color space.
<snip>
Not true if you use relative colorimetric with black point
compensation.
At least using the Adobe products splits the transform into two
transforms
source -> Lab, Lab -> destination.
False.
Adobe's BPC is done in XYZ, not LAB. The correction is wedged between
the two profiles. A single colorworld is still created - not two. So
image data is converted directly from device1 values to device2
values. It's like a devicelink profile that has been created in
memory.
I never said that BPC is done in Lab. Adobe's techdoc about
BPC clearly says that it's done in XYZ internally.
Fact is, if I use convert to profile in Photoshop CS2 from
Adobe RGB (1998), Matrics based, PCS XYZ to
ISO Coated v2 (ECI), LUT based, PCS Lab,
relative colorimetric with black point compensation,
my Logging Color Management Module on Windows AND Mac outputs
the following, which can be pretty much divided into the following
parts:
Computation of Black Point Compensation:
RGM CMM: src: Adobe RGB (1998), dst: Lab D50, srcRI: 1 dstRI: 1
RGM CMM: src: ISO Coated v2 (ECI), dst: Lab D50, srcRI: 1 dstRI: 1
RGM CMM: src: Lab D50, dst: ISO Coated v2 (ECI), srcRI: 0 dstRI: 0
RGM CMM: src: Lab D50, dst: ISO Coated v2 (ECI), srcRI: 1 dstRI: 1
Preview:
RGM CMM: src: Adobe RGB (1998), dst: Lab D50, srcRI: 1 dstRI: 1
RGM CMM: src: Lab D50, dst: ISO Coated v2 (ECI), srcRI: 1 dstRI: 1
Conversion:
RGM CMM: src: Adobe RGB (1998), dst: Lab D50, srcRI: 1 dstRI: 1
RGM CMM: src: Lab D50, dst: ISO Coated v2 (ECI), srcRI: 1 dstRI: 1
which are clearly two separated conversions running through my CMM.
Regards
Rolf Gierling
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