[opendtv] Re: New Chips Improve Color TV Dramatically

Weighing in on the color  discussion.

This thread has been very interesting. There are several things I 
would like to add from my experience working with these issues.

As a starting point, it is important to note the differences between 
display gamuts and encoding space gamuts. The traditional RGB color 
space that we are familiar with, thanks to decades of watching CRTs, 
has a significantly greater color gamut than NTSC or PAL. Many of us 
learned this the hard way from two "life experiences:"

1. Developing or working with video production equipment that 
includes color matte/background generators. many of these color 
generators were designed WITHOUT color gamut controls, thus they were 
able to output "illegal colors" for the NTSC and PAL color encoding 
spaces. A waveform monitor and vector scope were required in 
production control to make certain that the combination of color 
saturation and luminance did not exceed the limits imposed by the 
encoding system, and these limits varied based on the selected hue. 
We were able to create a software algorithm for control of 
matte/background generators in the GVG Model 100 that limited the 
output of the generators to ONLY legal colors.

2. Working in the RGB color space of computer graphics systems, many 
of which evolved into tools used to create video graphics. The gamut 
available in a 24 bit color system (8 bits per RGB channel) 
significantly exceeds that of NTSc, PAl and even the REC 709 color 
that is used today for HDTV. It is important to note that there is 
not a single unique RGB color space for computer graphics; the color 
space will vary based on the phosphor primaries used for the display.

The sRGB color space has come to dominate the computing landscape. 
This was an unfortunate turn of events, based in large part on the 
use of cheap CRT displays re-purposed from TV manufacturing lines. 
The sRGB space has strong parallels to the NTSC and PAL color spaces, 
due largely to the use of the same phosphor primaries. There are also 
issues related to the use of gamma settings that are "video friendly" 
rather than taking advantage of the full range of luminance values 
possible without the traditional video gamma curves.

Bottom line, there are huge areas of the RGB color gamut that are not 
legal with current NTSC/PAL displays and even many HDTV displays. 
Educating would be video artists in the fine art of selecting legal 
colors became an advocation as a writer covering the emerging world 
of PC based graphics in the late '80s and early '90s.

Later, as the TI DLP projectors evolved to provide good performance 
in the lower end of the greyscale, we also saw the potential to 
expand on the color gamut that could be delivered with these 
projectors when primaries were selected that extended the color 
gamut. One of the great things about microdisplay projection systems 
is that we are not locked into phosphor based primaries. With color 
wheels and color filters, almost any primaries can be used. I have 
seen many demonstrations of the improved color gamuts that are 
possible.

One of the most interesting was at a SMPTE Conference in Pasadena in 
the late '90s. The source was an animated movie. Two film-to-tape 
transfers were done; one used Rec 709 colorimetry, the other used and 
extended RGB gamut. The results on screen were dramatic, with much 
more intense color saturation.

Bottom line, there's a world of color out there ready to exploit, if 
we choose to. sRGB is a poor choice if we want to take fulll 
advantage of that world.

Regards
Craig
 
 
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