ld231782@longs.LANCE.ColoState.EDU (Lawrence Detweiler) (07/09/90)
----- ----- Can someone give me the standard wavelengths of the red, green and blue television/monitor phosphor emissions (or of the Macintosh color monitor in particular)? As long as we're at it, what is the range of visible colors in the electromagnetic spectrum? Also, since my earlier message got chewed (the mysteriously missing leading line) I will ask again: Is anyone familiar with a formula that, given known RGB wavelengths, can give the intensities (amplitudes) of the waves that most nearly approximate another wave (or even a superposition of multiple ones)? The original question was to map the visible range of the electromagnetic spectrum onto RGB values; but maybe this more specific phrasing above may ring some bells. (I'm making the assumption that RGB mappings are actually superpositioned wave approximations.) The description has a direct mathematical analogue to sine waves--is any stuff in Fourier analysis, etc. applicable? I have been informed that the problem has not been "satisfactorily" answered; I find this hard to believe. Please email responses; I will summarize upon request. ld231782@longs.LANCE.ColoState.EDU
tomg@hpcvlx.cv.hp.com (Thomas J. Gilg) (07/10/90)
> Can someone give me the standard wavelengths of the red, green and blue > television/monitor phosphor emissions (or of the Macintosh color monitor in > particular)? As long as we're at it, what is the range of visible colors > in the electromagnetic spectrum? International Commission on Illumination has: red = 700.0nm, green = 546.1nm, blue = 435.8nm Have seen other numbers such as 700.0nm, 505.0nm, 470.0nm Specs I have for a SONY Color Monitor (1280x1024) in CIEXYZ space are: red = ( 0.64, 0.33 ) +/- 0.02 grn = ( 0.29, 0.60 ) blu = ( 0.15, 0.06 ) white target = ( 0.283, 0.298 ) Range between 400 and 700nm usually. Depends on person/age. Thomas Gilg tomg@cv.hp.com
poynton@vector.Eng.Sun.COM (Charles A. Poynton) (07/26/90)
In article <101880022@hpcvlx.cv.hp.com> of Comp.graphics, Thomas J. Gilg <tomg@hpcvlx.cv.hp.com> replies to a query about monitor chromaticity. The poster of the original query asks: >> Can someone give me the standard wavelengths of the red, green and blue >> television/monitor phosphor emissions ... ? Gilg replies: > International Commission on Illumination has: > red = 700.0nm, green = 546.1nm, blue = 435.8nm This is true but misleading. Practical phosphors emit not just one wavelength but a complicated spectrum. Dominant wavelength is generally not a useful metric for monitors. Monitor people and colour transform calculations deal in CIE xyY coordinates, not in wavelength. Although they are probably sufficiently close for the poster's purposes, the CIE wavelengths given do not accurately represent any CRT phosphor set. > Specs I have for a SONY Color Monitor (1280x1024) in CIEXYZ space are: [numbers deleted ...] The numbers quoted comprise the standard EBU (European) phosphor chromaticity set. Sony makes -broadcast- monitors with this chromaticity set, but none of the Sony -computer- displays that I know of use that set. A few days ago someone on Comp.sys.mac.programmer asked a similar question; I attach my reply which includes the Sony numbers. I also attach my chromaticity crib sheet with a bunch of other chromaticity numbers; I enthusiastically welcome any new contributions! C. ----- 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. ----- >From: poynton@vector.Eng.Sun.COM (Charles A. Poynton) Subject: Re: Need color temperature specifications for Apple RGB monitor Newsgroups: Comp.sys.mac.programmer Summary: Bluer than blue, 9300 K. Here's the CIE xy chromaticity coords. All of the Sony computer displays that I have ever known have the following chromaticity coordinates: x y tol persistence 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. ----- MONITOR CHROMATICITY TABLE Charles A. Poynton 90/07/25 Original NTSC/FCC (circa 1953, no longer in use): x y R .67 .34 G .21 .71 B .14 .08 W .310 .316 (CIE Illuminant C, 6800 K) gamma light=volts^2.2 luma .299 R+.587 G+.114 B SMPTE RP145/Conrac "C" (current N.A. 525/60 broadcast television practice), also SMPTE 240M 1125/60 HDTV: x y R .630 .340 +-.005 G .310 .595 +-.005 B .155 .070 +-.005 W .3127 .3291 (CIE D65, 6504 K) gamma light=max[volts*4,((volts+0.1115)/1.1115)^(1/0.45)] luma .212 R+.701 G+.087 B EBU (current European 625/50 broadcast television practice): x y R .640 .330 G .290 .600 B .150 .060 W .3127 .3291 (CIE D65, 6504 K) gamma light=volts^2.8 luma .299 R+.587 G+.114 B [known not to match chromaticities] P22 phosphors (e.g. Hitachi HM-4119): x y tol persistence R .610 .342 +-.016 1.2 ms G .298 .588 +-.016 300 us B .151 .064 +-.016 250 us W .313 .329 +-.016 (6550 K +7 MPCD) gamma unspecified, typical 2.5? Sony Trinitron: x y tol persistence 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) gamma unspecified, typical 2.5? Mitsubishi: x y tol persistence R .618 .350 +-? Medium short G .280 .605 +-? Medium short B .152 .063 +-? Medium short W .283 .298 +-? (9300 K +8 MPCD) gamma unspecified, typical 2.5? Zenith 14" FTM x y tol persistence R .616 .336 +-? 470 us G .324 .580 +-? 41 us B .146 .066 +-? 40 us W .313 .329 +-? (CIE D65, 6504 K) gamma unspecified, typical 2.5? ----- 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. -----