Colour recovery from B&W kinescope films

[cbenham]

Originally Posted by Joel Cairo

So the short answer is: assuming the kinescope film was properly and professionally transferred, the full frames are all there-- it's just that their respective fields are slightly jumbled in places...
-Kevin

This thread began as a discussion of the process by which B&W kinescopes made from Pal colour video could be processed electronically to recover the
color information and restore the program to full colour.

This is only possible because both the PAL video system and the kinescope camera operate at 25 frames per second. Thus each frame of the resulting B&W film includes all of the video frames and fields, and more importantly the 8 field PAL colour sequence which is the key to the colour restoration process. Without the 8 field colour sequence recovery of the original colour program can not be done

In NTSC B&W kinescopes, the 4 field color sequence is lost because 12 video fields per second are not captured in the 30 to 24 frame per second conversion process thus breaking the color sequence and making recovery of the 4 field color sequence impossible.

If the original NTSC kinescope process had used a film camera operating at 30 frames per second then recovery of the 4 field color sequence would be possible and just as in the Pal kinescope method, the 30 fps NTSC kinescopes containing all the complete frames and fields, and more importantly, the 4 field color sequence could be processed to successfully recover the color signal.

Not being able to recover the 4 field color sequence from 24 frame kinescopes is the stumbling block in NTSC.

[Joel Cairo]

Originally Posted by cbenham

This thread began as a discussion of the process by which B&W kinescopes made from Pal colour video could be processed electronically to recover the
color information and restore the program to full colour.

This is only possible because both the PAL video system and the kinescope camera operate at 25 frames per second. Thus each frame of the resulting B&W film includes all of the video frames and fields, and more importantly the 8 field PAL colour sequence which is the key to the colour restoration process. Without the 8 field colour sequence recovery of the original colour program can not be done

In NTSC B&W kinescopes, the 4 field color sequence is lost because 12 video fields per second are not captured in the 30 to 24 frame per second conversion process thus breaking the color sequence and making recovery of the 4 field color sequence impossible.

If the original NTSC kinescope process had used a film camera operating at 30 frames per second then recovery of the 4 field color sequence would be possible and just as in the Pal kinescope method, the 30 fps NTSC kinescopes containing all the complete frames and fields, and more importantly, the 4 field color sequence could be processed to successfully recover the color signal.

Not being able to recover the 4 field color sequence from 24 frame kinescopes is the stumbling block in NTSC.

Well, not to put too fine a point on it, I think that the lack of color patterning on most NTSC kinescopes would be a much larger obstacle to the use of Richard's CR system... his telerecordings were created in a way that allowed the color signal to display itself as chroma patterning on top of the B&W luma signal-- ours (by and large-- there **are** exceptions) were not.

(But it's really a moot point anyway-- first you have to find US intellectual property owners that would actually pay for the upgraded [and necessary] HD transfers of their kinescoped materials in the first place... and believe me, **that's** probably not going to happen!)

-Kevin

[Aussie Bloke]

It's been very interesting reading all the posts in response to the subject, am learning a lot of great technical knowledge in regards to the kinescopes.

Something has just popped to mind, when BBC did experimental 405 line NTSC colour tests I am guessing (correct me if I'm wrong) that 16mm B&W kinescope films would of been made of those experimental casts. If it were true, I wonder if there might be a better chance (if a NTSC colour recovery program was made) of recovering the chroma off them films if the films were recorded to the same frame rate and there is patterning from the monitor?

[Joel Cairo]

Originally Posted by Aussie Bloke

It's been very interesting reading all the posts in response to the subject, am learning a lot of great technical knowledge in regards to the kinescopes.

Something has just popped to mind, when BBC did experimental 405 line NTSC colour tests I am guessing (correct me if I'm wrong) that 16mm B&W kinescope films would of been made of those experimental casts. If it were true, I wonder if there might be a better chance (if a NTSC colour recovery program was made) of recovering the chroma off them films if the films were recorded to the same frame rate and there is patterning from the monitor?

Theoretically, I suppose so-- however, the evidence I've seen appears to indicate that any kinescopes that were made of the after-hours BBC test broadcasts would only be of 16mm test footage and slides (as those were the sources that were broadcast), rather than actual programming, so I'm not certain there would be too much to gain in looking for such telerecordings... assuming they exist.

-Kevin

[NewVista]

Originally Posted by Aussie Bloke

http://www.techmind.org/colrec/
Makes me wonder ..a program ..to recover.. NTSC

Check out the diagonal lines on link foto; I'd forgotten how bad PAL was. With NTSC, dots don't align but are neatly 180 deg out of phase so TVs/ video effects can extract most luminance detail with a simple comb filter (can't do that with PAL). Also PAL decoding loses half chroma V resolution and every generation of co-dec displaces the chroma down one line! At least it's not as bad as SECAM which effects manufacturers wouldn't support.

[andy]

...

[NewVista]

Originally Posted by andy

The dots in PAL also line up 180 degrees out of phase on adjacent lines. .

It would have been good if they did, then PAL TV's could have implemented analog Y/C comb filters for sharper pictures since the 80's like the RCA Dimensia premium TV's since 1984

The NTSC developers foresaw this in the early 50s, but - 10 years later - the PAL developers screwed up - incorporating a 25Hz offset (to minimize dot crawl) resulting in an awkward 8-field 'Color Frame' sequence and really nasty artifacts like on those screen shots.

To comb filter a PAL TV, it requires expensive frame store digital processing chip-sets--not available until just before the phase out of PAL . Germany - where it started - ditched PAL for DTV a number of years ago.


Interesting link:
http://www.burnworld.com/dvd/primer/ntsc.htm

"Another important factor in choosing the new exact frame rate was to make sure that the color signal phase would be shifted exactly 180 degrees for each scanline. There are two reasons why this is important. First, the chroma signal does cause some distortion to older TV sets, especially those that were used at the time of the introduction of color TV and which didn't have notch filters to filter out the chroma information. In addition, early color tv sets (and newer cheap ones) suffer from imperfect luminance and chrominance separation, causing dots to appear near strong-colored edges. These dots are called creepy crawlies or, more commonly, dot crawl. They are particularly visible along vertical lines in the transmitted video, especially when SMPTE color bars are transmitted. The phase shift makes these dots non-stationary and thus reduces their visibility. The second reason to the phase shift is that it makes it possible to use a comb filter, which allows separating chrominance and luminance information with much better fidelity. While an exect 180 degree phase shift per scanline is not an absolute necessity for a comb filter to work, it makes implementation easier and also gives the best potential quality. This is a lesson that was later forgotten when developing the PAL color coding scheme. This probably didn't seem like a big omission at the time, since comb filters didn't become widely available in NTSC television sets before the 1980's (and, because of huge implementation difficulties, high-end PAL 100 Hz TV sets didn't get comb filters before the late 1990s). Nevertheless, the theoretical groundwork that made comb filters possible was there from the beginning"

[andy]

...

[old_tv_nut]

Slight correction about PAL chroma phasing:

The B-Y alternates from line to line due to the subcarrier frequency (plus has a slight offset due to the 25Hz frequency offset, which makes it slip phase slowly from the top to the bottom of the screen); the R-Y, due to "Phase Alternation by Line," does NOT alternate 180 degrees from line to line, and has only the slight diagonal offset due to the 25 Hz. This consistent phase should be very helpful in recovering the chroma from the subcarrier dots, I think.

The R-Y line-up can be analyzed in frequency domain also (perhaps making your brain hurt!) as modulation by a half-line-scan-rate (15625/2 Hz) square wave, which suppresses the original color subcarrier and sideband frequencies and creates double the number of sidebands, which are offset by +/- 7812.5 Hz. This can be shown (in either the frequency or time domain) to show that a simple one-line-delay comb filter will work for B-Y, but not for R-Y, since the R-Y dots line up just as though they were luminance stripes (except for that 25 Hz frame offset, of course).

You can draw some really pretty pictures of the 3-dimensional spectra (horizontal, vertical, and temporal frequency axes) of NTSC color and PAL color which show just what is necessary for comb filtering. but I'm not going to try that here. These also show all the flickering cross-color aliases for the two systems and show why some of the PAL crosscolor is more noticeable.

Edit: I forgot that the subcarrier frequency for PAL is also offset by a quarter cycle per line period to prevent the vertical line-up of the R-Y. Makes the cross-color not as bad as it could have been, but still a problem for comb filtering.

[dtuomi]

Actually most B&W kine's of color shows in the U.S. were made with B&W picture tubes. I had an engineer mentor of mine who used to get stuck babysitting one when he was a bad boy at ABC. Apparently they used blue phosphors in the tube because the film they used was most sensitive to that color (even though it was B&W).

Anyway, NTSC is real easy to notch filter out, and everyone did it to prevent the color info from causing any unwanted "random" patterns on the films. So almost no kinescopes of American color television would even have any color information in them at all.

David

[Joel Cairo]

Originally Posted by dtuomi

Actually most B&W kine's of color shows in the U.S. were made with B&W picture tubes. I had an engineer mentor of mine who used to get stuck babysitting one when he was a bad boy at ABC. Apparently they used blue phosphors in the tube because the film they used was most sensitive to that color (even though it was B&W).

David

At ABC and (until 1966) at CBS this was true, but NBC actually began shooting a portion of their kines off of color monitors starting back in the 50s.

And although CBS may have continued to use their old B&W kinescoping setups, once they switched over to color in 1966, they didn't really bother to filter their signals-- their kinescopes from that period forward are far inferior to the ones they produced in prior years.

- Kevin

[dtuomi]

That's interesting. I wonder if they were trying to use color film to capture the kine. I can't see any point in using one if you're just using B&W film. Anyway, I revise my statement, it was true of ABC.

David

[3Guncolor]

Also keep in mind most folks would be using quad video tape if there was a need to record live TV in the 60's. There would have to be a very good reason to use film kines they where bad for B/W and much worse for color.

[Joel Cairo]

Originally Posted by 3Guncolor

Also keep in mind most folks would be using quad video tape if there was a need to record live TV in the 60's. There would have to be a very good reason to use film kines they where bad for B/W and much worse for color.

Well, there were only three American networks at the time, so that really cuts down on the number of people that would be recording in the first place...

The reason for the creation film kines was usually due to:

1) Some affiliates (particularly those associated with ABC) couldn't afford the expense of videotape equipment for tape-delayed broadcast, so kinescope films were an inexpensive alternative-- they only required the use of a film chain, which was far more affordable in those days.

2) Kines were also created for program producers and sponsors, as a relatively inexpensive means to archive programs; and as a backup in the event that there was a question about something that occurred during the broadcast.

3) Even into the 60s, videotape remained a comparatively expensive format to utilize (much less archive); and really, it was essentially designed to be reusable-- so that's what people did.

-Kevin