[Tig] LUTs for Video File Codecs - ICC profiles

glenn chan glennchan
Thu May 4 10:10:45 BST 2006


--
Thanks to oktobor for supporting the TIG
--
While cheap CRT computer monitors have associated ICC profiles, that doesn't
necessarily mean that they display accurate color.

Three big problems that afflict cheap CRTs (in no particular order):
A- Aging of the CRT (related to how long it has been powered on).  The gamma
of the CRT will get darker and darker, crushing the blacks and making
shadows difficult to discern.  Dark text will be impossible to read.  You
can see this on many old CRTs... libraries tend to have a lot of CRTs like
this.
B- Non-standard phosphors.  i.e. 255(RGB) Red on one monitor is different
than red on another monitor.  The ICC profile for the monitor should reflect
this, but doesn't.
C- No calibration.  The decoding/interpretation of the analog VGA signal may
change over the monitor's life... the monitor will need to be properly
calibrated to reflect this.  However, many monitors lack the bias controls
(sort of like black level for each R, G, B channel) necessary to do this...
so you end up with something like reddish blacks.
Some monitors also can't change their white points.  I believe the computer
standard white point is 9300K.  Television/broadcast is D65, except in
Japan.  Even after adaptation, there is a noticeable difference between the
two white points... some consumer TVs implement "red push" to try to
compensate (they oversaturate the reds).

Glenn
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