mkelly@SKINNER.CS.UOREGON.EDU ("Michael A. Kelly") (07/22/90)
Does anyone have the color temperature specifications for the Apple 13" monitor (Sony Trinitron)? I need the CIEXYZ coordinates for red, green, blue, and alignment "white". Thanks a bunch, Mike. mkelly@cs.uoregon.edu
poynton@vector.Eng.Sun.COM (Charles A. Poynton) (07/22/90)
All of the Sony computer displays that I have ever known have the following
chromaticity coordinates:
x y tol persistance
R .625 .340 +-.030 1 ms
G .280 .595 +-.030 40 us
B .155 .070 +-.016 30 us
W .283 .298 +-.030 (9300 K +8 MPCD)
I doubt that either Apple or Sony publish these numbers.
For the colour neophytes out there, these numbers represent the absolute
colour reproduced for red, green, blue and white. One man's red is not
necessarily another's; chromaticity numbers are necessary to compute the
transforms from one colour space to another (even from an RGB space to a
different RGB space).
The RGB x and y values are solely a function of the phosphors of the tube.
The final row is the chromaticity of white, which represents the relative
contributions ("colour balance") among red, green and blue. Unfortunately
most computer displays are WAY too blue. Daylight has the same colour as a
chunk of platinum heated to 6500 kelvin, hence the CIE defined standard
illuminant D65 to have this "colour temperature". Modern blue phosphors are
about twice as efficient as red and green phosphors, with respect to the
sensitivity of human vision and driving all three electron guns in a colour
CRT with the same amount of beam current produces a picture that is about
twice as blue as daylight -- very noticeably blue. This is done to achieve
the maximum possible brightness, at the expense of colour reproduction. The
additional brightness over a more sensible choice of 6500 K is only about
5%, due to the eye's insensitivity to blue, but in a market that has
historically had little interest in accurate colour reproduction, a 5%
brightness increase was worth the penalty.
Experts can adjust their monitors for a CIE D65 white point by an internal
calibration adjustment.
If anyone out there has more interest in this stuff, I'll post more detail.
C.
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Charles A. Poynton Sun Microsystems Inc.
vox 415-336-7846 2550 Garcia Avenue, MTV21-10
fax 415-969-9131 Mountain View, CA 94043
<poynton@sun.com> U.S.A.
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