[argyllcms] Media white point? printer, monitor, camera
- From: Elle Stone <l.elle.stone@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 31 Jan 2010 16:18:53 -0500
Hi All,
I'm trying to understand "media white point" as pertains to a digital
camera matrix profile. How far off is what I've stated below? All
statements are relative to V111 or to versions before 110 in which the
-u switch did work with a matrix profile.
1) "colprof -aG (or "-am") -u ti3file" creates a profile with the
media white point set to be the same as the illuminant.
2) "colprof -aG (or "-am") ti3file" creates a profile with the media
white point determined by the nominally brightest patch on the target,
which for a Wolf it8 target is probably GS00.
3) For a printer profile, the brightest patch should be "paper white"
and truly reflects the media (paper) white point, that is, the color
of the paper.
4) For a monitor profile, the brightest patch should be
RGB_R=RGB_G=RGB_B=100.00 (taken from a monitor .ti3 file created for
profiling my LCD monitor in its native state). This is the whitest
patch the monitor can display, the color (media white point) of which
will depend on whether one is profiling a monitor calibrated to D65 or
some other target white, or whether one is profiling the native
behavior of the monitor.
5) For a camera? This is where I don't understand the logic of using
the nominally brightest (but not necessarily truly neutral a=b=0)
patch on the target to calculate the media white point. What or where
is the "media" whose white point is being calculated? The color of the
light itself seems the logical choice, but the far from neutral GS00
patch on my Wolf it8 target doesn't seem like a good choice of patches
for measuring the color of the light. The much more neutral GS06 patch
would seem a better choice. Or even better, if there was a way to get
ti3 values from a spectrally neutral white balance card.
Similar questions pertain to media black point. Any light cast (no pun
intended) on this puzzling topic is greatly appreciated.
Elle
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