Rca left everyone else at the alter

[tubesrule]

Hi old_tv_nut,
I think we're on the same page here. There are two effects that cause color seperation, movement in the source image using sequential scanning, and movement of the observers eyes, which is why I discussed these effects seperately. The source material issue can be controlled in a number of ways, one of which being using progressive material. The issue of movement of the observers eyes will always be a problem on field sequential displays like the CBS, DLP projectors, and many color industrial/medical displays currently in use. This is true when considering one effect at a time.

When considering both issues together, like the case of an object in motion with source seperation, and the observers eye following it, the background will have the expected seperation, but the object being followed will also show a color tail due to the persistance of a CRT. (assuming a CRT display type) This effect was observed during early testing using a computer generated, true 6 field sequential white square bouncing around the screen.

An interesting thing that came out of the demonstration last year was that the CBS color field rate seemed to be at the threshold of perception for some people. While many observers said they percieved no flicker or seperation, others said they could easily see the seperation. It would have been interesting to see how this effect would have been received 50 years later had the CBS system won out.

Darryl

Regarding flicker, I sometimes have trouble when viewing one of those automotive diagnostic scopes....you know the kind, the large machines at repair shops that display the spark plug firing lines.

I tend to see either a flicker or sometimes I don't see every line. Guess I don't have as much persistence of vision as others....although I more than make up for that with my persistence of annoyance!

Anthony

[old_tv_nut]

Yep, tubesrule - you have to consider the source and the display and what the eye is doing!

I went through some really dumb arguments with a person involved with the HDTV standards committees who insisted that progressive scan at 72 Hz would _eliminate_ judder on 24 fps film material. Well, it does not, although it is cleaner than the 12 Hz components you get with 3:2 pulldown and 60 Hz displays. I eventually wrote a little program to calculate the relative displacement over time oif the juddered images for any input and display rates.

I always hesitate pointing out the 3:2 judder to people who have not really paid attention to it, because once you notice it, it's hard to ignore.

By the way, film in theaters is shown with a double shutter so that the flicker rate goes up to 48 Hz. Some projectors have used triple shuttering to raise the rate to 72 Hz so the pictures could be brighter without visible flicker, but this usually results in poorer focus, as the film heats and expands between the three presentations of a single frame. Whether with double or triple shuttering, professional film makers are very careful to avoid bad pan rates or rates of motion across the screen, because the judder can look very bad. Micromirror pirojectors for digital cinema can eliminate much of this problem even when the source is only 24 fps, but good cinematographers still are careful.

For some of the tests of HDTV scan formats for the FCC ACATS, we used a ShowScan film, which is shot at 60 frames/second and therefore shows no judder when televised at 60 fps progressive. The ShowScan film is 70 mm, and at their facility they had a floor to ceiling screen that you viewed at about one picture height or less - much more detail than the 1 or 2 megapixel HDTV standards, and therefore an excellent, nearly transparent source material for HDTV tests.

[old_tv_nut]

Originally Posted by heathkit tv

Very early color film used a two color system...sometimes pretty effectively. Were there ever experiments with a similar arrangement for television?

Anthony

I believe Baird experimented with a 2-color electronic system in the 40's - have to go look it up. And there is a mention of a color system invented in Mexico, in their 1964 New York World's Fair brochure, which may have been 2-color.

Sometimes some of the very early two-color cartoons will show up on TV, but I have never seen one of the two-color live-action films televised.

[tubesrule]

Heh old_tv_nut,

"...progressive scan at 72 Hz would _eliminate_ judder on 24 fps film material. Well, it does not, although it is cleaner than the 12 Hz components you get with 3:2 pulldown and 60 Hz displays"

This does seem counter intuative doesn't it Changing rates is just such a hard thing to do, but native CRT 24fps HD displays have so much flicker That program you wrote to determine the judder sounds interesting.


"I always hesitate pointing out the 3:2 judder to people who have not really paid attention to it, because once you notice it, it's hard to ignore."

It also drives me nuts the way most broadcast TV is time compressed now with it's associated artifacts, but heh, if you can sell more commercial time per half hour, who cares


"By the way, film in theaters is shown with a double shutter so that the flicker rate goes up to 48 Hz."

That was such a cleaver method using a light cutter for reducing flicker in film, kind of like interlacing on television to reduce flicker, although interlacing has so many side effects.


"For some of the tests of HDTV scan formats for the FCC ACATS, we used a ShowScan film, which is shot at 60 frames/second and therefore shows no judder when televised at 60 fps progressive."

It's a shame that more film isn't overcranked, but few are willing to pay the price. Hopefully with the coming of HD more will be done in 720/60p. The sad part is the technology has progressed tremendously, but little can be said for the content


Hi Anthony,
Many of these industrial displays use light shutters or valves and do have a lot of visible flicker to them. One that comes to mind is a color Oscilloscope we have at work that is field sequential, and can be quite annoying as you look around at the front panel and see the three colors separate!

Darryl

[old_tv_nut]

Originally Posted by ceebee23

But on the other hand there would have been no phase error ..but then again extracting RBG would been fun ..and no saturation control....mmm...as for color fringing ...perhaps a quick check with the Early Television museum may clear that up ..as they have some CBS field sequential sets working????

Of course just as CBS did the blue banana trick RCA had swirling batons which very neatly showed this problem! ...aaaagh fun and joy

Having no phase error was true IF the camera tube discharged completely on each field. So, image orthicons worked OK, but vidicon cameras using a color wheel would have contamination from one color into the next, requiring a complex apparatus to store frames if you wanted to fix it. (Or I suppose you could cheat and change the colors of the filters slightly.)

Also, the bit about no convergence errors is only true if the power supplies in the receiver are good. They must have good high voltage regulation so the raster doesn't change size between fields, even if the scene is mostly one color. My old boss who saw the original CBS tests talked about this problem in receiver design. Also, the power supply had to be low ripple, because the 60 Hz line was not in sync with the sweep. The monitors we saw at ETF last year seemed OK in this regard.

[tubesrule]

[QUOTE=old_tv_nut]I believe Baird experimented with a 2-color electronic system in the 40's - have to go look it up. And there is a mention of a color system invented in Mexico, in their 1964 New York World's Fair brochure, which may have been 2-color.

Not sure of the model or make, but I remeber an early 2 color projection television at a store I worked at in the late 70's. It was an all-in-one, front projection unit in an upright cabinet, and the two crts pointed forward onto a small, flip down mirror that projected the image back onto the front of the screen at the top. Not sure how well I'm describing it, but I think it might have been a Sony. Maybe someone else remebers it.

Darryl

[old_tv_nut]

[QUOTE=tubesrule
Not sure of the model or make, but I remeber an early 2 color projection television at a store I worked at in the late 70's. It was an all-in-one, front projection unit in an upright cabinet, and the two crts pointed forward onto a small, flip down mirror that projected the image back onto the front of the screen at the top. Not sure how well I'm describing it, but I think it might have been a Sony. Maybe someone else remebers it.

Darryl[/QUOTE]

I think I remember a design that was actually 3-color, but two of the colors were combined optically through one lens???? Could it have been something like that?

[Sandy G]

Weren't the 1st color TV shots from the Moon-Apollo 12-NOT 11-done in field sequential color? Seems like I remember some sort of blather about that-may have dreamed it. 1969 was a LOOOOOOONG time ago...-Sandy G.

[tubesrule]

Originally Posted by old_tv_nut

I think I remember a design that was actually 3-color, but two of the colors were combined optically through one lens???? Could it have been something like that?

It's possible as I did not have the opportunity to look inside. I do remember that the two colors where cyan and a magenta/orange which would make sense. I think I remember being able to see the targets inside the crt's, but it was so long ago. I hope someone else remebers this set.


And you are correct about the 60Hz power line on a 24Hz television. This could cause all sorts of misregistration between fields. There was also a discussion last year about how relatively quickly the color filters would have faded in use, and since there was no tint or gain control, nothing could be done at the user end, so changing your filters may have become a common service call.
I also didn't realize that the CBS sets did not have a way of locking to the color signal, and you had a one in three chance of it coming up correctly. This means that just changing the channel between two CBS color stations (not that this ever happened) meant you had a 33% chance of the colors coming up right! The Gray Research monitor added a "red field" pulse to phase lock it's color wheel automatically, and it was pretty cool seeing this in action on Steve's set. I assume CBS would have adopted this method had they won out.

Darryl

[andy]

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[old_tv_nut]

Orange and Cyan would be right for a 2-color system. I was thinking maybe green in one lense and red+blue in the other.

The red field pulse was in the CBS system, just a matter of whether the receiver paid attention to it. I cna't believe that the recievers built by Zenith and used in demonstrations of medical color TV didn't have automatic phasing.

[domfjbrown]

Originally Posted by Sandy G

Weren't the 1st color TV shots from the Moon-Apollo 12-NOT 11-done in field sequential color? Seems like I remember some sort of blather about that-may have dreamed it. 1969 was a LOOOOOOONG time ago...-Sandy G.

Yep; there's an image somewhere of the camera, internal and external, with the colour wheel. Someone on here mentioned it a while back...

I have enough problems with flicker (due to my nystagmus) - I can see screen flicker and/or colour banding at 72 hz on many monitors, and our PAL TVs REALLY show up flicker on, for example, chrome trim on cars (a REALLY bad example is Robin Williams' car in "Mrs Doubtfire"!). That said, I'd rather have flicker at 50 Hz than digital nasties and smears at 100 Hz (I've still not seen a 100 Hz PAL TV I could live with - they all look crap even if they ARE stable!).

BTW - is it my imagination, or did the NTSC Region 1 version of "Blair witch project" NOT have the 3:2 pulldown effect on the hi-8 sourced bits, or am I imagining it (was very drunk when I watched it)? I *loathe* 3:2 pulldown, but I *really loathe* the BBFC, so would rather import a US film that's NOT been hacked with a chainsaw than get a 4% fast, censored to hell British cut of a film. "Enter the dragon" springs to mind - I got the NTSC version as I'd never seen the nunchuckers (sp?) etc - Nanny State Britain is so bad that even the "Teenage mutant ninja turtles" had to be renamed to "Teenage mutant hero turtles" (no, I'm NOT joking!). "Enter the dragon" is now out on UK DVD with the full scenes intact, but it took 3 years...