[FoRK] Breakthrogh in HDTV projector pricing

James Tauber jtauber at jtauber.com
Wed Jul 21 14:28:05 PDT 2004

The colour gamut is essentially the triangular part of a chromaticity
diagram formed by the choice of three points on or near the spectral
"horseshoe". There's a fair amount of variation theoretically possible
in the choice of the three vertices. In practice I believe it's largely
determined by the technology itself.

As I discovered recently, adding more primaries doesn't buy you more
colours because the parts of the chromaticity diagram outside a
well-chosen triangle (that you could get to with a five-primary
pentagon, for example) are indistinguishable to the human eye.

Interestingly, what appears to us as the same colour would appear
different to animals with different number of cones, however. Chickens
would need 12 primary colours, for example.

Furthemore, it only takes two colours to make white as long as the two
colours and white are colinear on the chromaticity diagram.

Bunch of great info on the CIE diagram at:



On Wed, 21 Jul 2004 14:14:53 -0700, "Dave Long" <dl at silcom.com> said:
> I was under the impression that color
> encodings for broadcast were based on
> human eye response, which would imply
> everyone's projectors would be using
> the same RGB frequencies. *
> Are there economic (or legal) reasons
> to use different sets of primaries?
> -Dave
> * NTSC, PAL/SECAM, and SMPTE look like
> they pretty much agree on R,B,W, with
> only NTSC G showing much variation.
  James Tauber               http://jtauber.com/
  journeyman of some    http://jtauber.com/blog/

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