Does HD playback affect Display color space needs?

Frank@N · 06-07-2006, 04:37 PM

I was looking at the Westinghouse 1080p monitor and noted that it only displayed 75% of the NTSC color gamut.

That might be OK for DVD, but doesn't HD playback have a wider color gamut?

Will there now be another standard...HD Color Gamut?

If so, web reviewers should start testing displays based on the more advanced color range.

Gregg Loewen · 06-07-2006, 07:07 PM

I started laughing out loud when I first read the 75% comment from Westinghouse.

NTSC does have a smaller gamut than HDTV, though it is not that very different, and certainly not a 25% difference. Please note that Westinghouse is claiming 75% of NTSC, which would be even less if measuring HDTV.

There are different specs for NTSC and ATSC (to answer your question).

I have NEVER seen another manufacturer boast about having less than full specs, usually a manufacturer will boast about having greater than full spec. In reality, greater than full spec is not useful, as spec is spec.

On a very related note, the Westinghouse is a good value display, that is not very color accurate, but its price is great.

Happy viewing!!!

Gregg

Frank@N · 06-08-2006, 10:11 AM

The 75% number came from a web review, but it's also listed under Specs on this Westinghouse link:

http://www.westinghousedigital.com/p...p-monitor.aspx

I believe other display technologies (DLP) are almost hitting full spec for NTSC color and many LCD/plasma models aren't far behind.

Anyway, 75% isn't very impressive and I'm surprised that HD sets continue to measured by NTSC standards.

ChrisWiggles · 06-09-2006, 12:31 AM

Yes, I thought that was a bizarre number I don't have any idea what they mean by 75% NTSC gamut. I would laugh at that just because it's probably not a meaningful number at all.

Also, be careful not to confuse old NTSC gamut with SMPTE C which is what standard definition content primaries are. BT.709 are slightly different for HD, however AFAIK all mastering is still done on monitors with SMPTE C phosphors, so gamut change for accurate HD playback is not really an issue yet. Some displays allow you to choose the gamut, which is an interesting feature.

Also, do not confuse the SMPTE C versus Rec709 primary chromaticity difference for the Rec 601 versus Rec 709 matrix difference. It is important to ensure that the proper color matrix is applied. It is arguably less important to ensure that the primary chromaticities are accurate for the content, since as mentioned one can assume that pretty much all HD content is still being mastered on BVMs with SMPTE C phosphors. It may be some time before that begins to change.

Allan Jayne · 06-10-2006, 09:59 AM

I would expect that for projection technology absolutely correct gamut can be achieved because a correct colored cellophane can be placed over the CRT or in a DLP color wheel. Whereas for direct view, the color is less accurate because getting the correct amount of color dye into each tiny pixel position is critical, or alternatively we have to rely on the color we can get from available phosphors.

For many years the red phosphor on CRT's was a little on the orangish side immediately resulting in a gamut that fell short in the red region.

Next we will need test patterns and a myriad of controls (similar to 100 point convergence*) to adjust the color video signal so it tracks the gamut properly.

* For example a horseshoe shaped CIE diagram with little colored circles superimposed on it and the person doing the calibration is supposed to make the color in each circle match the surrounding color.

Repeat, going back and forth iteratively, looking through red, green, and blue cellophanes that came with your AVIA DVD to make sure the little circles as seen still match the background they are over.

And the TV will need separate memories for HDTV versus analog broadcasts in order to save the laboriously done calibrations.

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