[HN Gopher] PAL Colour Recovery from black-and-white 'telerecord...
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PAL Colour Recovery from black-and-white 'telerecordings' (2008)
Author : madflame991
Score : 72 points
Date : 2022-08-28 09:53 UTC (13 hours ago)
(HTM) web link (www.techmind.org)
(TXT) w3m dump (www.techmind.org)
| Jaruzel wrote:
| This was used to good effect to 'recolour' the black and white
| versions of old Dr Who episodes due to the colour originals
| having been lost/destroyed.
| timonoko wrote:
| Black&White-tv was almost HD, 625x625. Then they added 3Mhz
| color-carrier in 1966 and it was 300x300 with this color-furze on
| top. This sucked so much. There was nothing I wanted see in
| living color. Especially winter-sports were mostly BW.
|
| I remember that color movies sucked also in 1950s. Technicolor
| has annoying fuzziness around objects. See Wizard of Oz.
| avian wrote:
| > Black&White-tv was almost HD, 625x625. Then they added 3Mhz
| color-carrier in 1966 and it was 300x300
|
| Maybe adding color did decrease the luma bandwidth and hence
| the horizontal resolution. I'm not sure about that. I think bw
| signals just used less bandwidth overall.
|
| But in no way did color decrease the number of lines in the
| image. Those are defined by the scanning raster and remained
| the same in color and bw television.
| Taniwha wrote:
| It's more obvious in US NTSC that the PAL being discussed
| here .... essentially the colour subcarrier was put way out
| in the high freq part of the luma signal - display - anything
| with too high a bandwidth and it stomps on the colour -
| you've all seen this happen on analog TV ... and it has had
| profound effects on fashion .... let me explain ...
|
| So what does "high frequency luma" mean? it means that the
| brightness of a signal horizontally along a line goes rapidly
| from dark to bright and back again - if that happens it
| stomps on the colour sub carrier and the colour goes wonky.
|
| S-video is just a cable that puts the 2 signals on different
| wires so this doesn't happen.
|
| So it turns out that the things that are the worst for this
| are things like checked or p;laid shirts/ties/dresses,
| tartans, houndstooth jackets etc etc - Think about what
| happened to fashion in the 70s/80s as colour TV became
| ubiquitous, people on TV started wearing solid colours, they
| didn't want to be the person who's whole body was a crawling
| mess - and people in the rest of the world started wearing
| the same sorts of styles - all those 50s/early 60s styles
| with checks and plaids you see on old game shows, all gone,
| not because of some big change in fashion - but because they
| could no longer be represented in popular culture.
| [deleted]
| stuaxo wrote:
| I remember going to the US in 1998 and being shocked at how
| bad NTSC TV looked compared to PAL, the colours just looked
| wrong.
| lb1lf wrote:
| Back when I used to moonlight in video production, the
| quip was that NTSC was an acronym for 'Never Twice the
| Same Colour'.
|
| The French SECAM system? 'Something Essentially Contrary
| to the American Method'
|
| I'll lead myself out.
| cf100clunk wrote:
| SECAM was also jokingly called "Systeme Electronique pour
| Confondre les AMericains"
| cf100clunk wrote:
| For technical reasons inherent in the chosen standard,
| NTSC TV sets required hue and color knobs, unlike PAL and
| SECAM. This effectively left it up to the consumer to
| adjust those values, with no accounting for variances in
| eyesight or taste. Unfortunately it meant that entire
| households had to endure the choices of whomever (Dad?)
| controlled the TV. On visits to others' homes it was
| painful to see how apallingly bad some peoples'
| preferences were. With PAL and SECAM the hue and colors
| were set to a standard, and that was that. Having said
| all that, the 29.97fps frame rate of NTSC was much easier
| on the eyes than the flickering 25fps of PAL and SECAM.
| Aloha wrote:
| NTSC adopted the color system it did because the cost of
| delay lines was considered to be too high, PAL also was
| more technically complex and probably would have delayed
| the adoption of Color TV, which was unacceptable to RCA.
|
| The US oft has this problem, we tend to be early adopters
| of technology on a wide scale, so by the time a thing
| comes along that solves most of the inherent problems in
| the v1, we already have a wide scale implementation of
| the thing. This happened with TV color, phones (24
| Channel T1 vs 32 channel E1 and aLaw/uLaw), credit cards
| (mag stripes), and all sorts of other things.
|
| SECAM had some real advantages, but made working with
| composite signals hard, because of their FM nature. PAL
| and NTSC are reasonably close conceptually, and frankly
| so is PAL, you can easily encode PAL into SECAM, because
| it's mostly the composite signals that are different.
|
| NTSC was originally 525 lines/60 fields per second
| (odd/even lines) giving an effective refresh of 30 fps,
| the 525 lines itself was dictated by our 6MHz channel
| width, and the field refresh by our 60Hz power. When they
| added color, they dropped the field refresh down to 59.97
| to deal with a beat frequency issue between the color
| subcarrier and the audio subcarrier.
| Aloha wrote:
| NTSC and PAL had very very different color gamuts.
| Taniwha wrote:
| Yes - in the US HDTV was a revelation for many people
| because of the much larger colour gamut, it was just so
| much better, in Europe is was mostly just bigger
| avian wrote:
| None of this supports the parent's claim that TV went "from
| black&white 625x625 to color 300x300", which is just wrong
| on several levels.
| timonoko wrote:
| > None of this supports the parent's claim that TV went
| "from black&white 625x625 to color 300x300", which is
| just wrong on several levels.
|
| Obviously no one here has experienced pure crystal-clear
| BW-tv and what happened when they turned the color-
| carrier on. You had to adjust the focus so that
| horizontal resolution was below 320. And of course the
| vertical focus was similarly affected, as there was no
| separate screws for that.
| fortran77 wrote:
| But there's some truth in this statement!
|
| The "Luma" resolution is, in theory 625x625, but the
| "chroma" resolution is approximately 1/4 of that. That's
| OK, because the way our eyes work.
|
| So "detail" remains at the 625x625 resolution, but the
| color information isn't that high. And our brains fill in
| the rest.
| tialaramex wrote:
| Digital video chroma sub-sampling _literally_ has quarter
| chroma resolution in 4:2:0 video which is or at least was
| fairly common for live action stuff. It 's obviously not
| going to be great for recording output from a computer,
| with sharp coloured edges, but live action scenes look
| fine.
|
| I don't think anybody would claim that their 4:2:0 Blu
| ray has "low resolution" because it used chroma sub-
| sampling.
| mhalle wrote:
| Crosstalk between luminance and chrominance signals are
| called dot crawl (chominance signal interfering with the
| luminance signal causing spatial artifacts) and chroma
| crawl (luminance signal stepping on the chrominance signal
| causing color artifacts).
|
| I believe chroma crawl was generally more of an issue with
| NTSC, if the luminance signal wasn't sufficiently band
| limited.
| timonoko wrote:
| > But in no way did color decrease the number of lines in the
| image.
|
| But it did. If you did not want to see the annoying 3Mhz
| color-carrier on your BW-TV, you had adjust the focus to 300
| horizontal lines, which affected the vertical focus too.
| timonoko wrote:
| Had to correct numbers:
|
| Super-good BW-TV was 625 x 625 x 25 = 10 Mhz. The color-carrier
| was 4.3 Mhz. So if you did not want to see the color-shit on
| your BW-TV, you had adjust the focus so that less than 625 x
| (4.3e6/(625 x 625 x 25)) == 275 horizontal lines were visible.
| TVs did not had separate adjustement for vertical focus. So all
| you really had was 270x270 TV.
|
| Except of course there never was 10Mhz TV-channels. It was
| below 8 Mhz, which was needed for full color. So there was
| moment of time, when we could enjoy 8Mhz black and white for a
| year. Almost 600 horizontal lines. And then they turned the
| color on and party was over.
| adrian_b wrote:
| Actually in the 625-line TV standard there are only 576
| visible lines.
|
| The other lines are for the vertical retrace, when the video
| signal is blanked.
|
| With square pixels, the B&W image would have been 576 x 768,
| which requires a 7.5 MHz analog video bandwidth (@ 50 Hz
| vertical & 15625 Hz horizontal frequencies).
|
| Most 625-line B&W TV sets could display 576 x 768 images very
| well and some of the early personal computers with video
| outputs for TV used this format.
|
| Nevertheless the broadcast TV signal was limited by a low-
| pass filter to lower horizontal resolutions, corresponding to
| 5 MHz analog video bandwidth in Western Europe and to 6 MHz
| analog video bandwidth in Eastern Europe. The reason was to
| provide space in the TV frequency channel for the audio
| signal, which used a carrier offset from the video carrier by
| 5.5 MHz in Western Europe and by 6.5 MHz in Eastern Europe.
|
| So the broadcast B&W signal was worse than what the B&W TV
| sets could display, corresponding to 576 vertical pixels by
| about 510 to 620 horizontal pixels (depending on the
| country).
| hilbert42 wrote:
| In Australia before the official introduction/launch date of PAL
| colour television in 1975 it was a requirement of the then, now
| defunct, broadcasting regulator, the ABCB - Australian
| Broadcasting Control Board for television stations to remove any
| colour content from their TV broadcasts. (During the conversion
| period leading up to the launch stations would run a mixture of
| B&W and colour material within their stations).
|
| To comply, stations would strip the colour burst from the TV
| video sync block before it was broadcast. This infuriated many
| propeller-head techies and nerds, myself included.
|
| To overcome the problem, the 4.43 MHz colour subcarrier in the
| broadcast video which wasn't deliberately stripped out was used
| to reconstitute the colour burst. This was achieved by modifying
| standard PAL colour TV sets (which weren't that difficult to
| obtain) with the addition of some subcarrier-extracting filters
| and appropriate phase-locking/modifying circuitry. This was a bit
| tricky, as the reference phase was no longer there and the fact
| that it was a PAL signal (PAL - Phase Alternating Line encoding).
|
| In fact, I recall at the station I was working for at the time we
| had a modified TV set in the engineering department working in
| colour from off-air signals (one of my colleagues was a past
| master at tweaking up sets this way).
|
| Perhaps a bit of broadcasting history trivia but it sure shows
| the colour recovery technique in this story wasn't the first
| effort.
|
| _Edit: Incidentally, the same trick was used on source material
| such as quadruplex videotape that already had the burst stripped
| at other locations._
| dannyw wrote:
| What was the benefit / reasoning for removing colour content?
| hilbert42 wrote:
| The usual bureaucratic crap, the government wanted the kudos
| - grand opening etc. There was also the legitimate problem
| that some stations would be ready before others and thus have
| a leading economic advantage. (Also, there had to be a
| reasonable supply TV sets available.)
| maratc wrote:
| Can't speak for Australia, but Israel in 1970's considered
| colour television as "a luxury that would increase social
| gaps"[0], and a similar colour burst erasing happened. This
| has lead to a rise of anti-erasing devices that reconstructed
| the colour burst, returning the colours.
|
| [0] https://en.wikipedia.org/wiki/Color_killer
| immibis wrote:
| Wow, caring about social gaps. Unthinkable today.
| CamperBob2 wrote:
| Unthinkable because government control at that level of
| granularity is such a stupid and downright offensive idea
| to begin with, or because it just plain doesn't work?
| zymhan wrote:
| False dichotomy alert
| immibis wrote:
| Yes, unthinkable because people generally find that the
| idea of fixing social problems is offensive, and just
| blame the victims for not fixing the problems they are
| suffering from.
| [deleted]
| powlow wrote:
| This is from 2008 - what are the newer developments in this
| space?
| dehrmann wrote:
| Since it should be easy-ish to synthesize training data, I'd
| think combining this with deep learning could produce some good
| results.
| cf100clunk wrote:
| Digitization, colourization, audio resampling, and other
| computer-based treatments of original recordings have taken
| over as restoration techniques from what are now archaic
| analogue-based techniques.
| dannyw wrote:
| A great video series on analog TV and color:
|
| https://youtu.be/dX649lnKAU0
|
| https://youtu.be/InrDRGTPqnE
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(page generated 2022-08-28 23:01 UTC)