1953 NTSC Color Gamut

[old_tv_nut]

Originally Posted by pidade

Thanks for the reply.

I think you may have answered this in your third point, but did receivers *always* adjust decoding of NTSC signals for newer phosphors after the '60s, even in the '90s or '00s, or was it ever designed out of the standard, i.e. encoding directly for SMPTE-C, receivers decoding without assuming 1953 NTSC? It seems nonsensical that they would continue encoding for, really, a dead standard decades after the last full NTSC sets were produced, but then if they did alter the target, that would probably wreak havoc with receivers that adjusted decoding.

Also, is "R-Y, B-Y, G-Y" just the decoded R'G'B' in the receiver?

Analog NTSC receivers continued to have modified decoding until the end.
The major decoding adjustment is increased R-Y gain to compensate for the excess of effective red content in the yellower green phosphor. Because the yellowish green was like having extra red whenever the green was turned on, it reduced the hue shift between red and green. The R-Y signal controls the balance of red in a given color, so increasing R-Y means that the difference in red as the transmitted hue changes is emphasized. This only works up to a point with the non-linear CRT and new phosphors, because 1) it can't really change the hue of the pure yellow-green phosphor when pure green is called for, and 2) it adds too much red on bright red colors.

R-Y, G-Y, and B-Y should really be all primed, e.g. R'-Y', because they are derived from R', G', and B' in the encoder, but the primes are usually omitted, just like they are for I and Q. They are the color difference signals that are derived from the chroma signal in the receiver, and can be obtained either by wideband IQ demodulation and matrixing or by equiband direct demodulation on the appropriate three different axes. These three color difference signals are then added to Y' in the receiver to get R', G', and B' drives for the picture tube. The CT-100 did the adding in external matrix circuits and then drove the 15GP22 grids. In many tube receivers that followed, the final addition was done in the picture tube by applying Y' to all three cathodes and R-Y, G-Y or B-Y to the appropriate grid (G1). Later tube designs that did not have separate grids required adding the Y' and color difference signals in the circuits before driving the picture tube cathodes.

R-Y, G-Y and B-Y are not independent, and any one can be derived from the other two, just as any one can be derived from I and Q. So some tube sets had R-Y and B-Y demodulators with a matrix for G-Y, a few had a different choice of the two axes and matrix, and a few had three separate demodulators and needed no matrix.

RCA chassis from CTC-7 onward for several years used a clever matrix that included DC restoration for the signals, but had some cross coupling between R-Y and B-Y outputs, so the demodulator axes were adjusted to compensate, and were called X and Z axes. The signals to drive the CRT grids then came out to be R-Y, G-Y and B-Y, but were adjusted further in later chassis to get approximate compensation for the newer phosphors, as discussed in previous posts.

[pidade]

Originally Posted by old_tv_nut

Analog NTSC receivers continued to have modified decoding until the end.
The major decoding adjustment is increased R-Y gain to compensate for the excess of effective red content in the yellower green phosphor. Because the yellowish green was like having extra red whenever the green was turned on, it reduced the hue shift between red and green. The R-Y signal controls the balance of red in a given color, so increasing R-Y means that the difference in red as the transmitted hue changes is emphasized. This only works up to a point with the non-linear CRT and new phosphors, because 1) it can't really change the hue of the pure yellow-green phosphor when pure green is called for, and 2) it adds too much red on bright red colors.

R-Y, G-Y, and B-Y should really be all primed, e.g. R'-Y', because they are derived from R', G', and B' in the encoder, but the primes are usually omitted, just like they are for I and Q. They are the color difference signals that are derived from the chroma signal in the receiver, and can be obtained either by wideband IQ demodulation and matrixing or by equiband direct demodulation on the appropriate three different axes. These three color difference signals are then added to Y' in the receiver to get R', G', and B' drives for the picture tube. The CT-100 did the adding in external matrix circuits and then drove the 15GP22 grids. In many tube receivers that followed, the final addition was done in the picture tube by applying Y' to all three cathodes and R-Y, G-Y or B-Y to the appropriate grid (G1). Later tube designs that did not have separate grids required adding the Y' and color difference signals in the circuits before driving the picture tube cathodes.

R-Y, G-Y and B-Y are not independent, and any one can be derived from the other two, just as any one can be derived from I and Q. So some tube sets had R-Y and B-Y demodulators with a matrix for G-Y, a few had a different choice of the two axes and matrix, and a few had three separate demodulators and needed no matrix.

RCA chassis from CTC-7 onward for several years used a clever matrix that included DC restoration for the signals, but had some cross coupling between R-Y and B-Y outputs, so the demodulator axes were adjusted to compensate, and were called X and Z axes. The signals to drive the CRT grids then came out to be R-Y, G-Y and B-Y, but were adjusted further in later chassis to get approximate compensation for the newer phosphors, as discussed in previous posts.

Some fascinating reading in all of the engineering involved in analogue color TV, thanks for the insight. Literally couldn't find any information about modified NTSC decoding outside of a vague mention here or there in a couple ITU or SMPTE papers, though it seems kind of significant.

Was there ever a standard set for this modified decoding, considering the phosphors used were generally fairly consistent across different tubes from the '70s onwards? I also wonder how white balance affected it (FCC specified CIE Illuminant C, SMPTE specified D65, TV manufacturers generally went for ~D93). I found this 1969 patent, though it could just be one of many kinds of decoders (or unrelated).

[pidade]

I guess, to help wrap my head around this, it would be very roughly equivalent to a modern camera shooting for Rec.2020, being graded at the studio on Rec.709 monitors essentially doing an on the fly internal conversion, possibly a lot better than they could back in the NTSC days, being transmitted as Rec.2020, and then being received at home on a Rec.709 display doing its own conversion?

[old_tv_nut]

Originally Posted by pidade

... Literally couldn't find any information about modified NTSC decoding outside of a vague mention here or there in a couple ITU or SMPTE papers, though it seems kind of significant.

Was there ever a standard set for this modified decoding, considering the phosphors used were generally fairly consistent across different tubes from the '70s onwards? I also wonder how white balance affected it (FCC specified CIE Illuminant C, SMPTE specified D65, TV manufacturers generally went for ~D93).

Some papers on modified chroma decoding were published in the IEEE Transactioins on Broadcast and Television Receivers.

The SMPTE-recommended switchable matrix for monitors was the only standard one I know of. TV makers did their own thing, based on their own subjective views. One of the things that affected the TV makers decision was the decidedly cyan white balance of receivers for many years. The subjective effect of white balance is dependent on surround conditions, which vary greatly in the home. The effects are much smaller in a dark theater environment with a screen occupying much of your view.

Referring to it as D93 is incorrect, as the D series of daylight colors had not been established. It was labeled as 9300K + 27 mpcd. This means it coreesponds to a black body color at 9300K and an adjustment perpendicular to the black body locus towards blue-green by 27 minimum perceptible color differences. It really was Illuminant C with the red reduced, so it was off the daylight locus toward cyan. This was strictly a measure to reduce the ratio of red gun current to the other guns, as obtaining daylight color ran the risk of spot blooming in the red highlights. Professional monitors could get away with actual daylight white (and unequal beam currents) because they weren't intended to be searchlight-bright in a store showroom. Not all manufacturers used 9300K. One of Zenith's secrets was its specified white point, which was less blue than others. Some manufacturers (Mitsubishi large screen rear projectors in particular) maintained the extreme cyan white balance forever, even when most others were offering a customer choice of a cool or warm (at least not so blue) setting.

[etype2]

I find this entire subject interesting. It is my understanding that the 1953 color gamut standard was never exploited even to this day. While DCI P3 comes close, Rec. 2020 exceeds the 1953 color gamut. I see a clear difference in NTSC 1953 green on my 15GP22 compared to my modern displays.

This Power Point by ISF (Imaging Science Foundation) address the subject well.
https://visions4netjournal.com/wp-co...-2017-33.3.pdf

[etype2]

Recently we re-read the RCA VS PHILCO court case, Re: Apple Tube. Philco built many CRT’s and each had unsatisfactory tech notes from the engineers, too hazy, fringe, rosey cast, green cast, bullseye, etc., and labeled unsatisfactory. As evidence, the lawyers showed photographic exhibits of screenshots of the Apple tube and an industry standard fruit bowl image used by Philco, Westinghouse, GE, RCA, Admiral and others.

I found the fruit bowl image and believe it to be a reproduction of the original NTSC color image from an unknown color CRT, but probably RCA’s image from their prototype 15GP22.



Here is a prototype Philco with a “rosey” image of the same fruit bowl. We found an image at last.



I’d like to order up a copy of the court transcript from the National Archives, hopefully to retrieve reproductions of the various screenshot images. However the transcript may only mark the photographs as EXHIBIT A,B, C and so on.

EDIT: An excellent link with additional images and commentary.
https://sterneworks.org/Mulvin-Sterne-Scenes.pdf

EDIT: 1949 RCA
https://visions4netjournal.com/wp-co...1A8942AA2.webp

1950 RCA
https://visions4netjournal.com/wp-co...F02E14EAA.webp

One more: Faye Emerson screenshot off RCA experimental television during a later trial to the public.

[old_tv_nut]

I just read a few bits of Mulvin-Sterne and think it should be taken with a grain of salt. It is an earnest attempt to analyze sociological aspects of color TV development, but some of its claims about the choice of test slides and names given to them are a stretch, and ignore the obvious.

For eample, they expound on the name "motion" for a slide of two running little boys that was obviously a still image. The obvious reason for naming the slide motion is not that anyone thought it would represent a live moving image, but because an evocative name is needed for each slide for quick and easy reference in conversation.

They also fall in the trap of assuming that the predominance of white people in the images meant that the reproduction of dark skin tones was ignored. This is only partially true, as it was well known that shading and black level balance in the early cameras could produce color shifts in darker colors. While this was not studied with Black models, it was continually studied with test charts, and live (white) models were chosen for their dark hair shades. For example, Marie McNamara, the most famous NBC "Miss Color TV" had dark auburn hair that was specifically noted as difficult to reproduce well as camera circuits drifted.

I need a more thorough read of this report, obviously, but I wonder if they give equal time to the difficulties of rendering blond hair without a green tinge in live broadcasts?

[old_tv_nut]

Regarding the request the NTSC made for additional slides with strong green elements:
It is well known that fairly satisfactory color images can be made with the Q channel turned off, since skin tones (light or dark) lie on or near the I axis. But the need to keep skin tone hue consistent was known to Kodak as well, resulting in film formulations that suppressed any tendency to shift skin towards green or magenta. As a result, most slides that would have been available would have little strong green or magenta content.

The provision of slides with plants against light and dark backgrounds would also be a substitute for critical shifts in color balance with dark and light subjects including skin tones. This is not to say that the lack of dark-skinned subjects was totally compensated by the range of test slides used. It certainly would have been an improvement to include a range of skin tones. However, there were similar problems in shadow color balance and contrast range in color film. If you review photography texts of the time, it is always stressed that exposure must be adjusted for photos of dark skinned people, and photos of groups with mixed skin colors usually needed careful lighting to not disfavor darker or lighter skin. Simple snapshots with non-adjustable cameras always had variations in skin tone, both White and Black. Professional photographers would control lighting and exposure and also use color balancing filters that were determined by Kodak and specified with each batch of professional film. Even then, precise results could not be achieved with slide film, as the processing could still affect color balance. Precise film color was only achieved in negative/positive processes where the color of the print was adjustable by trial and error. Color TV was held to a much stricter standard, as the off-balance could be adjusted in real time by turning the right knobs.

The problem of precise balance in darker tones was repeatedly raised over the years; advertisers of wood furniture complained when magazine images didn't match what they wanted. Dark skinned people have (rightly) been dissatisfied with the poor tolerance on their skin tones, but it really has not occurred because the problem was ignored, but because it is much more difficult to control the balance of dark tones in film (where dye concentration is max) than light tones.

In movies, the problem was reduced by throwing money (personnel and time for print adjustment) at it.

In television and eventually movies and still photography, the problem has been reduced with each major development in camera technology; first better analog cameras for TV, and then digital cameras for TV, movies, and amateurs.

[etype2]

Re: Your comments Wayne.
Agreed, I detected bias.
And now we are about to enter HFR (high frame rate) which should reduced artifacts generated by correction algorithms. Micro LED. Non organic, elf emitting (no backlighting, no filters) color displays.

[dtvmcdonald]

etype2: "And now we are about to enter HFR (high frame rate) which should reduced artifacts
generated by correction algorithms. Micro LED. Non organic, elf emitting (no backlighting, no filters) color displays. "

Who the f***gerund cares? Except for the rare BluRay disk, all
moving signals one gets are utter, complete, abysmally awful, infuriatingly bad,
intentionally horrible. I have seen no good quality signals recently from any purveyor
be it OTA, cable, or anything, except Bluray disks or direct playback from my Canon
5D Mk3 of scenes I myself took. The Canon pictures are stunningly good on either my
semi-calibrated computer monitor sold specifically for Photoshop work, my 55 inch Sony TV (LCD) or
my CT-100 (lower resolution).

All else is pixellated terrible resolution trash. Single OTS transmitters transmitting up to 9 channels!,
some with three so-called HD channels and a couple of SDTV ones for old episodes of "Bonanza" or
"Dick Van Dyke Show" (yes, the Dick Van Dyke of the appliance store
just down the I74 me.)

Even the NFL conference finals were pixellated crap from all sources. Like in one case the
football itself seemed to disappear!

And did I mention that Xfinity boxes are buggy? [living and breeding German cockroaches]

That's what program material purveyors think of quality.

[ChrisW6ATV]

Originally Posted by dtvmcdonald

That's what program material purveyors think of quality.

High-quality displays and improved technology can and will be used for high-quality video content, and many of us appreciate the improvements as we pursue such high-quality content.

It seems to me that a big difference between the early days of color-TV development/broadcasting and today, is this: In the 1950s they wanted/needed to create the best possible signals and displays (within the limits of technology and potential consumer budgets) in order to convince the public to buy into color TV at all. But, in the 2020s, there is little need to put real quality into most live/ongoing content, since most customers pay relatively little attention to quality in such content these days. (One could argue that it has been that way all along; remember how most people set their color TV sets for garish, excessive pictures for decades, and how they just accepted B&W TV sets without DC restoration, and so on.)

As you said, most live/ongoing content these days has pathetically low quality. I have always figured "you get what you pay for", so I cannot complain about over-the-air audio or video quality since it is all free. But that same logic is why I do not use -any- pay-TV (or paid satellite radio) services. Plenty of Blu-Ray and UHD discs and CDs are very high quality by comparison.

[etype2]

“ High-quality displays and improved technology can and will be used for high-quality video content, and many of us appreciate the improvements as we pursue such high-quality content.”

Agree. Look for it and you will find it.

Another analogy. The pursuit of perfection is a human trait that all of us strive to achieve in some form or fashion. We cannot rest on our past achievements and dismiss new ideas. As audiophiles seek excellence in sound, a subset of folks seek out the best available video equipment.

With regard to Wi-Fi signal content, high speed internet is a must to start with.
Research will show that fiber cable is the best available transmission service at the moment.
Service provider, Apple TV currently offers the highest bit rate transmission at the moment.

[Titan1a]

Broadcast television is the very last place you'll ever find quality pictures. Even VCR's with abysmal video s/n do better.

[KentTeffeteller]

Originally Posted by Titan1a

Broadcast television is the very last place you'll ever find quality pictures. Even VCR's with abysmal video s/n do better.

What VCR and it's picture are you discussing? Home machines running color under, and with their jittery picture aren't it. Once upon a time, even 3/4" U-Matic was not broadcast legal. Time Base Correctors changed that. Before they were affordable to TV stations, you usually used 2" Quadruplex and later 1" when Type C became the standard.

[Titan1a]

Discussing prerecorded VHS or Beta using a nearly new or well maintained player. It's obvious that recording bad quality over the air on a good recorder with quality tape is a waste unless the program would merit this. BTW I once saw first-rate television at 1080p from the ISS on cable before the resolution was dropped to 720i. I've never seen anything so good on any broadcast media since. Buy a 4K TV for this? You're throwing money away! Buy a used 720K CRT set or go back to radio! You don't need HiFi for mono news.