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Old 01-03-2005, 01:38 PM
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Questions on brightness of old colour TVs

Hi all. I've in the past read about the early colour sets including RCA CT-100 giving rather dim pictures and people have to watch programs with the light switched off to give a bright picture.

Just wondering between say 1954 and 1965 which colour tellies gave bright pictures and which gave dim pictures. I heard that the CT-100s gave low current emissions to the tube, was this corrected when the 21-CT-55 was released?

I also looked at the propaganda of the 60s colour TV ads advertising colour tellies saying they give much brighter picture than any of the previous ones. What is the truth in this?
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Old 01-03-2005, 03:10 PM
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My understanding is they could,early on, get a bright green & blue but getting a bright red was a challenge. They had to scale back the green/blue to match. Then in the early 60s they came out with rare earth phosphors which allowed brighter reds, so all 3 colors could be boosted. I think the tube in the CT-100 was especially bad due to its unique construction, with extra layers of glass between the electron beam & the viewer. Gradual improvements, in both the crt's & the electronics, came along the way.
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Old 01-03-2005, 10:24 PM
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Here's a long reply, so take a break first, sit down with a drink and a snack, and read on!


There were a continuing series of color tube improvements over the years, involving not only phosphors but also the tube construction. Of course, when a big advantage was obtained by one company, others had to adopt it to stay competitive in that wall of TVs at the appliance store.

In the very first phosphors used experimentally, the red was so poor that a color filter was needed over the faceplate. By the time NTSC was adopted, this wasn't needed, but the red still needed about twice the drive of the green or blue. The green at that time was a willemite P1 green, more a pure green than used presently, and having a rather longish decay.

One early change was to go to all zinc-sulphide phosphors. The green became more yellow, and also had a shorter persistence, matching the other colors more closely in this regard. The red was somewhat more efficient, I believe, but nowhere near the later rare-earth reds.

The introduction of rare-earth red phosphors was a major revolution in brightness. ( I'm not sure off the top of my head, but I think Sylvania was first.) Now the current ratios fo the three guns was more nearly equal, and, depending on the white set-up color, the green might need a bit more current than the red. Also, it was discovered that adding cadmium to the green sulfide phosphor increased its efficiency, at the expense of making it even more yellow. This moved the cyan edge of the color triangle towards white, so really saturated cyan colors could not be produced. The Newport cigarette pack is an example of a color that is in the original NTSC gamut, but outside the range of modern phosphors (but cigarettes can't be advertised on TV now, anyway!). Cadmium was dropped eventually, because of problems of handling this toxic element, so tubes went back to the plain sulfide green, which gives a good gamut of colors, not quite as wide as the original NTSC.

Zenith introduced the black-matrix "negative guardband" tube. Black matirix means the phosphor dots are surrounded by black material to reduce screen reflectance. Negative guardband means that the phosphor dots are smaller than the holes in the shadow mask. Since the dots might vary in light ouptput over their surface, you could get color errors in old the positive guardband case when magnetic fields would make the electrons land on different parts of the phosphor dot, so purity adjustment was more critical. Essentially, the negative guardband tube allowed higher beam power for more brightness, since shadow mask expansion could go further before causing a problem. RCA, I believe, introduced invar shadow masks in some tubes, also as a measure to reduce effects of mask heating. The ultimate in this regard was the tension mask, which does not undergo any distortion until it becomes hot enough to relieve the pre-tensioning and sag.

Sylvania, if I remember correctly, had good results with changing the physical processing of the phosphors, adjusting the particle size and the thickness of the slurry used to deposit them. The thicker slurry required extra care to prevent swirl marks due to uneven application.

Sony's Trinitron introduced the tensioned shadow grill, which was more transparent to the electron beams and increased brightness (but lost contrast because the ratio of black matrix to phosphor area decreased). It also had an improved electron gun that could produce a better spot size at high currents. Better electron guns for the shadow mask tube were also developed, and the shadow mask tubes went to in-line guns and striped phosphors. The use of in-line guns made the vertical deflection of the electrons irrelevant to purity adjustments (if the beam moves vertically, it just stays on the same color stripe). This new degree of freedom allowed the development of self-converging deflection systems that needed no circuitry or adjustment once the yoke positon was set at the factory. This was a major breakthrough in reducing the cost of color TVs.

Projection TV introduced new problems, since the sulfide phosphors (blue and green) tend to saturate and produce sub-linear output at high current densities (highlights go pink). this was solved in varioius ways by using non-linear circuits (mainly in the blue) or new phosphor formulations (mainly in the green).

The changes in phosphor color over the years, in order to obtain improved brightness, had effects on the color reproduction. It is possible to correct exactly for a change of phosphor primary colors, but this has to be done at the camera before the signals are "gamma-corrected" to match the non-linear electrical characteristics of the picture tube electron gun. When PAL was standardized, they settled on current phosphors (including the non-cadmium sulfide green). NTSC, however, has been operated under the FCC dictum that the encoding is "suitable for" the original NTSC phosphors. Therefore, receiver designers have put adjustments in the color decoder. The problem is that since sulfide green is too yellow, it's like getting some red you didn't want in every mixture of red and green, including fleshtones. So, you have to increase the R-Y color-difference gain, so when it goes negative (reduces red and increases green), you really reduce red a bit more. That means that when you increase red, you also increase it more than you would before. If everything were linear, this would be just right to correct the reproduced color. However, because of the non-linear characteristic of the electron gun, the turn-on gets enmphasized more than the turn-off, resulting in overly bright reds, while flesh tones and less saturated colors are correct. This situation has finally been corrected in the new HDTV standards, which have settled on a set of primary colors very similar to the PAL colors. These primary colors have also been carried over into digital cameras (and computers to some extent) as the "sRGB" standard.

By the way, although the green phosphor color has changed the most from the original NTSC, the blue has changed also, toward violet. This is sufficient to change fleshtones slightly greenish, since the yellow obtained from mixing red and green must be complementary to the blue phosphor. This change is also standardized in PAL and HDTV. The red has also wandered a bit toward orange and back, but it is still close to where it started. (By the way, traffic-signal red has always been outside the range of reproducible colors.)

The change in white color over the years is also worth mentioning. The NTSC settled on Illuminant C, an approximation to the light from an overcast day. (The modern equivalent is D65.) Nearly all sets from the earliest 21-inch RCAs onward, however, went to 9300 degrees Kelvin, which is quite blue. (Some had another preferred setting, but it typically wasn't Illuminant C.) This was partially a result of matching the black and white sets that people had gotten used to, partially to make the whites look "whiter", perhaps partially because 9300K is what you could get with reasonable current ratios for the three guns, and perhaps because the reds, yellows, etc really look brightly saturated when compared to a bluish white. The drawback is that color errors in fleshtones are exaggerated. One thing that drives videophiles crazy today is that some manufacturers still set the white point quite blue.

All the above applies to CRTs. Plasma screens use different types of phosphors that respond better to the UV discharge, and may have somewhat different primary colors. The first ones had much oranger red than CRTs. LCDs and micromirror (DLP) devices depend on the spectrum of the light source combined with color filters.
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Old 01-03-2005, 11:37 PM
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Thanks guys for the answers. Old TV Nut, your detailed response is very interesting in deed, certainly explains a lot.

One interesting thing I noticed with modern computer monitors is that when I've scanned a 12p emerald green UK queen head stamp on my scanner I don't get a matching emerald green, it looks like it has somewhat slightly more yellow in it, here's a couple of shots from a site of the stamp I'm talking about:


As you's notice they aren't as emerald as the actual stamp itself. I guess the phosphors you mention explain why a beautiful emerald green cannot really be achieved.

Just wondering though, the pure willemite P1 green phosphors, did it produce a nice emerald green colour to match that of a emerald 12p UK queen head stamp???
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Old 01-04-2005, 01:14 AM
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I know for sure that sets from from the early 60's on had pictures that were perfectly watchable in normal room lighting.
I hope to see a working CT-100 in person someday so I can report back on it
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Old 01-04-2005, 09:23 AM
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My buddy Steve D. has a working CT-100 and I've watched it several times. Works fine in normal light just like any color TV, old or new.
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Old 01-04-2005, 10:54 AM
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Yes, a brilliant pure emerald green cannot be achieved. The question of what particular color is actually displayed is much more complicated - was it sensed correctly by the input device? What color within the range of reproducible colors should it be translated to? In your case, the over-all system result moved its hue toward yellow. A correct hue (but with reduced saturation) might be more desirable. These considerations are of very practical importance when the color monitor is being used to represent some other reproduction device, such as the restricted range of newspaper inks. It is generally considered less important for the cases of objects that are outside the range of the monitor, since these are normally man-made and not likely to be a concern in ordinary pictures of scenes and people.

This is the subject of color managment systems. When dealing with these issues in Photoshop, for example, you may choose a working color space, and colors outside the range will be indicated on the monitor. Photoshop has a wider-range choice than sRGB, but the input device also has to support it, of course.

Colors that are unreproducible have to be translated to something, and this will be determined by the "rendering intent", a choice of an algorithm that maps input to output colors. For example,the rendering may compress mainly the colors that are outside the range, or it may compress all colors in some way so that their relative saturation percentage is maintained, etc. etc. It is not only the hue and saturation that have to be accomodated, but the brightness or density range. Reflective objects generally can have high saturation at low brightness but not at high brightness, while CRTs can have high saturation at high brightness, but not at low brightness (due to stray light reflectance).
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Old 01-04-2005, 10:57 AM
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Another note: the P1 is generally described as emerald green; don't know what the actual color of the stamp is, though, so can't say for sure if it is reproducible - however, my guess is that the P1 green would do it.
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Old 01-04-2005, 12:12 PM
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Old TV Nut, you were right... Long read! But very, very interesting!

I really don't know how they can say what any color "looks" like, since you can only describe a color by relating it to another... In other words, imagine trying to explain "blue" to a person who has been totally blind all thier life? It would be like trying to explain a mythical color like "koorange"* to anyone else.

This is making my head hurt.

*If I ever invent anything, I'm going to name it "koorange, plahboragne, etc" because I want to ruin that rule about "nothing rhymes with oragne".
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Old 01-04-2005, 02:49 PM
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Quote:
Originally Posted by old_tv_nut
Here's a long reply, so take a break first, sit down with a drink and a snack, and read on!
Thanks for the warning......I was beginning to prairie dog before I read your post!

Quote:
The change in white color over the years is also worth mentioning. The NTSC settled on Illuminant C, an approximation to the light from an overcast day. (The modern equivalent is D65.) Nearly all sets from the earliest 21-inch RCAs onward, however, went to 9300 degrees Kelvin, which is quite blue. (Some had another preferred setting, but it typically wasn't Illuminant C.) This was partially a result of matching the black and white sets that people had gotten used to, partially to make the whites look "whiter", perhaps partially because 9300K is what you could get with reasonable current ratios for the three guns, and perhaps because the reds, yellows, etc really look brightly saturated when compared to a bluish white. The drawback is that color errors in fleshtones are exaggerated. One thing that drives videophiles crazy today is that some manufacturers still set the white point quite blue.
This brings up something I've always noticed......you ever go by someone's house or apartment at night and see a darkened room lit by the TV? It's always blue light with flashes of color as the scene changes. It was the same way with B&W sets. Go figger. Thanks for the great post BTW!

Anthony
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Old 01-04-2005, 05:05 PM
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You are so right!

The basic science of color **reproduction** (get the basic meaning?) is color **matching**, that is how do you take a mixture of three primary colors and make it look exactly like the original color (match it or reproduce it), even though the spectra may be completely different. You have to be able to do this first, before making any of the appearance corrections mentioned below.

You are right, the way a color looks depends on the visual environment. This observation is the basis of more recent "color appearance" models that attempt to determine how the color should be reproduced in a new environment so it looks like it did in the old environment. There are a lot of things going on in the human visual system that affect these results, some of them very weird. For example, you might think that in a room lighted with orangey incandescent light bulbs, the TV reproduction should be adjusted to the same orangey white. (After all, a photograph seen in this light has all its colors biased towards orange.) But NO! when you do this to a TV, it looks way too orange - something more towards daylight-white color looks better.

NTSC, because of the phosphor changes, has for many years violated the first criterion of being able to accurately match colors over the whole range simultaneously(mostly that green phosphor change bieng compensated at the receiver instead of the transmitter, and a few other things like overly-blue white color, partial DC coupling in older sets, etc.). The phosphor errors mean that the viewer can match one or two colors to his/her preferred memory (usually fleshtones and near-by colors), while other colors have errors (strong reds too bright, cyans too dim)

PAL, and the new HDTV transmissions, at least get the color-matching capability reasonably in hand, so appearance adjustments can be made based on that. Since both the studio and the home viewer are then viewing the same reproduction, there is a chance for the artistic people to decide how they want things portrayed and get that result at home (or for the technical people to just be assured that the set-up is accurate). This standardization also makes possible the good results that are obtained with digital still cameras these days.
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Old 01-04-2005, 08:21 PM
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Last edited by andy; 12-08-2021 at 04:12 PM.
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Old 01-04-2005, 08:50 PM
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I made a post about color reproduction a while back on this one TV I have. It is this 1972 Sears 8" portable color solid state set I have. It has a delta gun tube, and no black matrix. I made sure and double checked that I had proper greyscale and background setups. I try to set all my sets for 6500K for a neutral white. I used a split field NTSC EIA color bar pattern to adjust my color saturation and hue properly. I have the brightness and contrast adjusted correctly. What clearly stands out is the green is actually green and not yellowish. It is a very distinct difference that stands right out. And the red is actually red and not orangish. Blue looks about the same, but looks like it has more contrast in it. What I have noticed is the yellow reproduction is a bit weak. But overall, it looks very different and good.

This is the only TV so far I've seen look this way. Forgive me on this as this is the oldest color set I've used in my life so far. It is a Japanese make, and the picture tube # is 250TB22.

Last edited by tv beta guy; 01-04-2005 at 09:36 PM.
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Old 01-06-2005, 11:10 PM
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>>>I've been disappointed to see that HDTVs still let you (mis)adjust the color and tint even on digital signals. I was hoping the switch from NTSC to ATSC would finally put an end to those adjustments. There is absolutely no need for them since there is no way for the color to get shifted in transmission. I wonder if the factory defaults will even be correct, or if they will insist on sticking to a massively oversaturated picture?>>>

Probably just done for people's differing tastes, plus you can still be watching some old show or film on an HDTV that is faded, tinted, color normally tinted but washed out etc. from age or inferior color control on old tv shows. Not that I've ever needed to tweak my HDTV set just for that but I guess it's a legitimate argument. Plus tubes, plasmas etc can age differently in the 3 colors can't they? So wouldn't you need to possibly tweak them a little over time? Sure not as much as people needed it in 1959 or something where every channel was tinted slightly differently due to the accuracy back then in transmission, but I definitely want any set I own to be adjustable as per color...Frenchy
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Old 12-08-2007, 04:39 PM
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Remembering old_tv_nuts excellent contribution in this thread, I have created a plot showing the different gamuts for NTSC color television and PAL color television. When you compare the color triangles for NTSC and PAL, you can see that the color space for NTSC is larger than for PAL. Especially the difference for the green point is the farthest. The coordinates in the color triangle for NTSC (1954) are red .67, .33, green .21, .71 and blue 0.14, 0.8. The coordinates for PAL (1974) are red .64, .33, green .29, .60 and blue 0.15, 0.6.

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Last edited by yagosaga; 12-09-2007 at 05:06 AM. Reason: coordinates in color space added
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