I don’t think the top graph is representative of what a typical 3 chip prism camera does.  The spectral sensitivities should overlap and with steep slopes/transitions.

What the F23 might be doing (I don’t know; Sony should publish its spectral sensitivities) is that the transitions are less steep.

2- In practice, color accuracy is difficult to achieve due to metamerism (unless we go with some impractical system that has a lot more than 3 primaries).  Metamerism would occur at many points in the signal chain… metamerism from the lighting source, the object illuminated, (lens), sensor, monitor phosphors (or equivalent), and the viewer’s eye.  We could potentially reduce metamerism caused by the camera by going with something like the RGBE sensor in Sony’s F828 digital stills camera.  But it would be unnecessary because nobody cares, and nobody notices.  And our video systems have all sorts or color inaccuracies anyways… this would be one of them: (post houses not doing SD <—> HD conversions according to standards)
http://www.glennchan.info/articles/technical/hd-versus-sd-color-space/hd-versus-sd-color-space.htm

3- You don’t really want your camera to see more spectra.  Where metamerism in the camera is unacceptable is when black doesn’t appear black due to sensitivity to infrared.  This is noticeable and people complain about it.  In 3 chip prism cameras, the camera manufacturer could extend the spectral senstivity into the infrared range to increase the camera’s overall sensitivity to light (and in some applications this might be useful).  So this is something to watch out for with 3 chip prism cameras… figure out to what degree the manufacturer has done that.

The camera seeing more spectra isn’t really a good thing.

4- NTSC is not the problem.  The problem is that consumer TV manufacturers don’t make color accurate sets (arguably for good reason when TV sets were dim).  The color space article touches up the changes in the standard primaries.

The new wide gamut TV sets that are appearing will screw things up more… some TVs will take normal gamut material and oversaturate it (except for memory colors) because otherwise the wide gamut capability would go unused.  And this signal processing probably doesn’t obey the principle of constant luminance, causing saturated colors to be too bright and appear neon (the Sony OLED seems to do this when I briefly saw it; could be wrong there though).
A fundamental problem with wide gamut is that consumer TVs will vary in their gamut size.  So even if the signal processing were perfect, some TVs will show colors that other TVs aren’t capable of showing.

Posted by GlennChan  on  08/21  at  12:50 PM

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