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Old 6th Mar 2008, 9:03 pm   #1
dave walsh
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Default B+W Telerecordings in Colour

Today's Technology Guardian reports that colour info can now be recovered from 16mm prints. Chromadot errors from the original transfer to b+w film can be used to regain colour info! Not colourisation but the original colour recording apparently! 13 episodes of Dr Who/Steptoe and Son have been done plus more interesting stuff like Nigel Kneale's "Year of the Sex Olympics" predicting the Big Brother era [CH4 that is]. Dave W
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Old 6th Mar 2008, 9:17 pm   #2
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Default Re: B+W Telerecordings in Colour

Full story here:-

http://www.guardian.co.uk/technology...6/research.bbc

Fascinating stuff...

Regards, Mick.
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Old 6th Mar 2008, 9:34 pm   #3
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Default Re: B+W Telerecordings in Colour

It makes sense. If you've ever looked at colour bars on a good monochrome monitor the different colours have very obviously different dot crawl patterns. The hard part is recovering what are likely to be some very faint residues of the dot pattern. It implies that the resolution on the film was high and must suffer badly from whatever methods were used to conceal the line structure.

Having got a good scan of the film it's case of throwing enough processing power at it to see if you can recover enough information to get useful colour.

Another approach that's been used to recover colour is to marry up the decent quality luminance from a film telerecording with the poor quality chrominance from domestic and other low quality VTRs.
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Old 8th Mar 2008, 7:42 pm   #4
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Default Re: B+W Telerecordings in Colour

Thanks for the link.
It's nice to know that this can now be done.
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Old 9th Mar 2008, 12:32 pm   #5
ENGLISH VICTOR
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Default Re: B+W Telerecordings in Colour

What an interesting report Dave posted and what important thoughts Jeffrey added regarding the recovery of colour from B.W. telerecordings, I read the full story "Thanks Mick for the pointer" I add to the problems already noted the following: Almost undreamt of horizontal linearity will be required even using the so called self referencing chroma lock techniques. There will be no reference burst captured on film because the monitor will have blanked it during H retrace and even if the monitors flyback were fast enough it would not have been displayed or filmed. The gamma of the best telerecordings I have seen are quite poor, usualy compressing high luminance levels i.e white, yellow and cyan.
Added to the above because of the need to avoid line aliasing and the visibilty of chroma crawl steps were normaly taken to minimise the chroma dot pattern being recorded, this often comprised the use of a fairly sharp notch filter at S.C. frequency leaving only chroma transients visible on the film. No niceties such as vel comp or chroma tec as used with tape are helpful and finaly we must not forget the physical accuracies needed on film proccesing and re scanning.
If what I have written seems to put the proposed idea in a negative light it is because the concept when analysed is fraught with problems, however I have learnt never to say "It won't work" because it just might.
I presume all the copies of Dr. Who and the other material that is to have it's colour reclaimed would have had the recording operator make the same error of switching off the chroma filter on the telicine monitor because without it there would be no dot pattern to process. Note also chroma filtering was also used to prevent halftone errors being recorded on film during high saturation scenes.
Finaly , filmed secam now that could be interesting!!!.
Victor.
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Old 9th Mar 2008, 1:09 pm   #6
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Default Re: B+W Telerecordings in Colour

At a slight tangent I remember someone from Philips R & D telling me
years ago that when ITV did a "Black & White" strike around 1970
preventing programmes recorded in colour being transmitted in colour
(think staff wanted more Pounds Shillings & Pence for colour TV working) basically the colour burst signal was removed/attenuated but everything
else was transmitted & colour could be recovered.
Don't think the Beeb were involved in this strike
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Old 9th Mar 2008, 2:29 pm   #7
dave walsh
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Default Re: B+W Telerecordings in Colour

I'm heartened by these responses. A lot of people just seem to want to get on with restoration work-fair enough on a great site like this of course
but there is always a wider picture [no pun intended].
I have [if any at all] more knowledge of technology history than actual theoretical understanding-can't even post the link for example.
Also I've got the time to pick out fascinating bits like this which I do at least understand the implications of [I think].
I still remember the time when even the prospect of making home video recordings seemed like an unimaginable dream!
Recovering a video signal like this is not quite on a par with getting Dinosaurs from DNA I realise but then who knows where software developements might go in the end-think of the "Stone Tapes" TV program. This is probaly more on a par with the decoding of early 30 line Baird TV images from 78's a few years ago-another surprise!
Will we ever recover lost layers on wiped 2" Videotape? Very far fetched I agree but what a difference this would make to the BBC's ["I'm sure we did have a copy once"] Archive. In the meantime it will be interesting
to see what else the Beeb can get back into colour. Aside from the B+W
transfers, I have recently seen one or two programs that I didn't even realise had been made in colour in the first place!

Devotees of the Blade Runner film [any version] may recall software processing that takes the detective into a video image of a room, into a mirror on the wall and effectively outside the frame and round the corner...we are not quite there yet but who knows? Dave W

Last edited by dave walsh; 9th Mar 2008 at 2:42 pm.
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Old 9th Mar 2008, 6:08 pm   #8
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Default Re: B+W Telerecordings in Colour

There was an article in the August 1976 issue of Television describing Chroma Lock Decoding where the colour information is extracted and decoded without using the PAL burst to lock the colour subcarrier.

It was apparently used by a small number of enthusiasts in Australia to decode PAL encoded signals with the burst suppressed before Australia officially went colour.

Keith
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Old 9th Mar 2008, 8:19 pm   #9
Andy Green
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Default Re: B+W Telerecordings in Colour

I suppose the principle of recovering lost colour is similar to colourising old Black and White films (which is a practice that is well advanced) - the main difference is that instead of guessing the colours, the software can get a 'clue' as to the correct colour to use. I would imagine that the process doesn't actually add the colour by decoding the PAL signal in the conventional way.

Dead interesting though!

With regard top recovering wiped tapes - this could theoretically be done also - techniques exist to used to recover wiped data on computer hard disks, it would then be necessary to use digital processing techniques to artificially improve the signal to noise ratio wich would be very poor.
= Certainly not beyond the bounds of possibility

Further reading of this technique (after originally posting ) says that it is definitely NOT similar to colourisation.
However, often two ways of conceptualising a solution to a problem end up essentially being the same - the matrix method and switching method of FM stereo coding, for example - mathematically they are almost identical.

Last edited by Andy Green; 9th Mar 2008 at 8:32 pm.
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Old 9th Mar 2008, 9:04 pm   #10
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Default Re: B+W Telerecordings in Colour

It is indeed fascinating. It seems, having heard some info from James Insell, that the same process could be applied to the 1950's 405 line NTSC tele-recordings, as the chroma dots are also present in those, so we may we be able to see the 405 NTSC tele-recordings restored to full colour.
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Old 10th Mar 2008, 11:50 am   #11
ENGLISH VICTOR
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Default Re: B+W Telerecordings in Colour

Replying to Keith it may be of interest to know that I was one of a number of people involved in the development of chroma lock techniques, not sure why the article appeared as late as Aug 76 because the official start of Colour was April 1 1975, I guess the time wasn't relevant. At the time of my development work I was working at one of Sydney's comercial T.V. channels, ATN 7. but my work was private and involved taking my one inch much modified Ampex VR7003 to work and dubbing British colour programmes from tape to my private one inch Ampex using full bandwidth recording and colour error correcting during replay without burst, some months later I was able to recover burst from one of the two inch high band recorders. I thus had a source of colour material that enabled me to emulate off air P.A.L with no burst present whenever I needed it. Time frame about 1970.
The burst was not removed by the T.V. stations on purpose it simply did not emerge from the VTRs because they were not fitted with color tec etc. and the station transmitter along with the studio equipment would have blanked out the burst in any case.
Hoping that was of interest to someone. I don't claim to be the inventor as I believe the technique was first described prior to my work by a German company for incorporation into a professional studio decoder.
Victor.

Last edited by ENGLISH VICTOR; 10th Mar 2008 at 12:03 pm. Reason: Vital word missing from the last sentence "inventor"
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Old 10th Jun 2008, 11:10 am   #12
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Default Re: B+W Telerecordings in Colour

ENGLISH VICTOR, do you have any other information, references or links regarding decoding colour without reference to the colour burst? I'd like to try this digitally, but see no reason to "re-invent the wheel" if a good method has been discovered before.

As you mention the 1970s, it gives me some comfort that I wouldn't be stepping on anyone's patents.

Many thanks for your help.

Cheers,
David.
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Old 10th Jun 2008, 1:35 pm   #13
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Default Re: B+W Telerecordings in Colour

This will give you some idea of the results to date:

http://colour-recovery.wikispaces.co...olour+recovery
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Old 10th Jun 2008, 3:56 pm   #14
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Default Re: B+W Telerecordings in Colour

Thank you for that link Paolo - that's fascinating.

I was hoping ENGLISH VICTOR could provide some information on the "simpler" task of decoding a video signal without the colour burst which he mentioned, rather than the more challenging topic discussed at the start of this thread (working from a film frame with the geometry and line structure of the original video signal hidden).

Cheers,
David.
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Old 11th Jun 2008, 12:08 am   #15
dave walsh
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Default Re: B+W Telerecordings in Colour

Although I don't even follow a lot of this very well, I'm glad I flagged up the original article because the potential seems to be still very much unexplored [as I tried to suggest with my crude cinematic analogy].Actually I expected the experts [like ENGLISH VICTOR and everybody else] to say this is rubbish! Thanks Paulo! Keep it coming please.
Dave W

I've taken the liberty of sending an e-mail to E Victor. [In my experience, this can get peoples attention when they aren't watching the site anymore].
I'd like to know what he thinks as well.

Last edited by dave walsh; 11th Jun 2008 at 12:27 am.
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Old 11th Jun 2008, 2:03 am   #16
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Default Re: B+W Telerecordings in Colour

Quote:
Originally Posted by DoctorWho View Post
It is indeed fascinating. It seems, having heard some info from James Insell, that the same process could be applied to the 1950's 405 line NTSC tele-recordings, as the chroma dots are also present in those, so we may we be able to see the 405 NTSC tele-recordings restored to full colour.
Hopefully the line structure won't have been hidden in these films, as is the case with many early telecine recordings - meaning it will be possible to recover the original "signal" as it were!


BG
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Old 11th Jun 2008, 12:40 pm   #17
ENGLISH VICTOR
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Default Re: B+W Telerecordings in Colour

2Bdecided,
I have only just noticed the query from early this year. Basicaly instead of using reference burst a synthesised reference is generated by employing the chroma signal.
Both U and V signals from the 1H delay add and subtract circuits are frequency doubled to remove phase ambiguity and then limited in an attempt to remove some of the amplitude modulation, one of the signals will need to be phase shifted to match the other, the two signals are then added together producing an 8.8672 MHz signal this is then frequency divided by 2 to bring it back to 4.4336 MHz. the signal is then used to phase lock the xtal reference generator throughout the entire line rather than during back porch period. This is only a very rough sketch of the principle I employed and does rely upon manualy correcting U and V phases. I used to re- form the missing Bruch burst and combine it with the composite video and record it for future use on a standard pal receiver.
BTW the system was far from perfect but produced acceptable pictures when BW was the alternative.
I should mention that the burstless composite signal still needs to be fairly stable, I think the max error from the B.W. playback VTRs was of the order of 15 ns 30ns max from the tv station.
Victor

Last edited by ENGLISH VICTOR; 11th Jun 2008 at 12:51 pm. Reason: Spelling error
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Old 11th Jun 2008, 12:51 pm   #18
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Default Re: B+W Telerecordings in Colour

Lack of burst is the least of the problems when trying to decipher the colour dot crawl pattern from a telerecording.

Decades ago there were chroma lock decoders that could decode a PAL or NTSC signal in the absence of burst. If the signal is otherwise in good condition this isn't particularly difficult.
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Old 11th Jun 2008, 12:52 pm   #19
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Default Re: B+W Telerecordings in Colour

Thank you ENGLISH VICTOR - I think I understand that.

From what you've said, i.e. that it "does rely upon manually correcting U and V phases", it sounds like you hit the same problem the Colour-Recovery guys hit - i.e. which quadrant is it supposed to be in? I assume with a stable source you'd only have to "tell" it once, rather than having the problem re-occur all over the frame as in the present Colour Recovery from film work.

Is that right, or have I misunderstood?

Cheers,
David.
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Old 11th Jun 2008, 12:55 pm   #20
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Default Re: B+W Telerecordings in Colour

Quote:
Originally Posted by ppppenguin View Post
Decades ago there were chroma lock decoders that could decode a PAL or NTSC signal in the absence of burst. If the signal is otherwise in good condition this isn't particularly difficult.
Please share some links or further info if you have it - I know it's off topic, but this is exactly what I'm looking for. If it works well for NTSC too it might be different from what ENGLISH VICTOR has described.

Cheers,
David.
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