I've just watched a clip (https://www.youtube.com/watch?v=_P09xG1clcg -
no, it wasn't to my taste) where clearly there is a significant time
offset between chroma and luma. It occurred to me that, when nowadays if
the only extant copy is a digitised version (the original analogue having been lost, or its source unknown), it'd be quite an interesting challenge
to correct it: I don't think there's anything in the digital domain that's analogous to the luma/chroma split, so presumably the chroma and luma
would have to be regenerated, then slewed back into approximate alignment.
(This one is slightly unusual in that the chroma appears to _lead_ the
luma rather than the usual lag.)
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf
interracial marriage was still illegal in 17 states in 1967.
I know what you mean. Some VCRs tended to smear the chroma and pulsate it as >well.
Brian
In message <u6juna$16m0b$1@dont-email.me> at Sat, 17 Jun 2023 10:28:23,
Brian Gaff <brian1gaff@gmail.com> writes
I know what you mean. Some VCRs tended to smear the chroma and pulsate it >>asI don't remember seeing a pulsating one! Though a multigenerational copy could get horrendous pretty quickly. Chroma _lag_ was common - I think
well.
Brian
most memorably on snooker; one got used to seeing a grey ball, with a
ghostly coloured one to its right, especially in a long shot (where a
fixed chroma offset was of course more noticeable).
My post was really just thinking - if all we have is a digitised copy,
it might be an interesting task how to correct such material, whether
it's chroma lag or lead (presumably both of similar difficulty).
I think the days of retrieving e. g. lost Dr. Who episodes from private copies were mostly still in the analogue days, or at least where the machinery in which the two signals were present was still in use, even
if the actual re-syncing was done digitally. (I think the most
fascinating aspect of that work was when someone realised that black-and-white film copies might still contain the colour subcarrier.)
"J. P. Gilliver" <G6JPG@255soft.uk> wrote in message >news:MNs1rVg1XZjkFwCi@255soft.uk...[]
My post was really just thinking - if all we have is a digitised copy,
it might be an interesting task how to correct such material, whether
it's chroma lag or lead (presumably both of similar difficulty).
I think the days of retrieving e. g. lost Dr. Who episodes from private
copies were mostly still in the analogue days, or at least where the
machinery in which the two signals were present was still in use, even
if the actual re-syncing was done digitally. (I think the most
fascinating aspect of that work was when someone realised that
black-and-white film copies might still contain the colour subcarrier.)
Digital colour photographs and videos are still stored as luminance and
some form of chrominance difference. And often the colour resolution is
half the luminance resolution in one or both directions, as for
analogue video.
It ought to be fairly easy to write a program that shifts the chroma
pixels sideways a bit compared with the luminance.
If you take a still photo (eg a JPEG or PNG) and make a black and white
copy, you can subtract this from the original photo (most image-editing >software such as Paint Shop Pro or Photoshop can do this), you can see
how blurred the remaining colour info is after you've subtracted the >luminance.
Here's an example: a colour photo of the famous clock on the city wall
in Chester, then a black and white version of it and then colour minus
BW (adding on 128 to each pixel to avoid "pixels with a negative
value"!) leaving just the chroma.
https://i.postimg.cc/7Y1Q6h1C/Chester-Colour.jpg >https://i.postimg.cc/1XhJR1fc/Chester-BW.jpg >https://i.postimg.cc/gjV4nth9/Chester-Colour-minus-BW.png
In message <u6kc37$18dig$1@dont-email.me> at Sat, 17 Jun 2023 14:22:32,
NY <me@privacy.invalid> writes
"J. P. Gilliver" <G6JPG@255soft.uk> wrote in message[]
news:MNs1rVg1XZjkFwCi@255soft.uk...
My post was really just thinking - if all we have is a digitised copy,
it might be an interesting task how to correct such material, whether
it's chroma lag or lead (presumably both of similar difficulty).
I think the days of retrieving e. g. lost Dr. Who episodes from private
copies were mostly still in the analogue days, or at least where the
machinery in which the two signals were present was still in use, even
if the actual re-syncing was done digitally. (I think the most
fascinating aspect of that work was when someone realised that
black-and-white film copies might still contain the colour subcarrier.)
Digital colour photographs and videos are still stored as luminance
and some form of chrominance difference. And often the colour
resolution is half the luminance resolution in one or both directions,
as for analogue video.
I didn't realise that was still the case.
Here's an example: a colour photo of the famous clock on the city wall
in Chester, then a black and white version of it and then colour minus
BW (adding on 128 to each pixel to avoid "pixels with a negative
value"!) leaving just the chroma.
https://i.postimg.cc/7Y1Q6h1C/Chester-Colour.jpg
https://i.postimg.cc/1XhJR1fc/Chester-BW.jpg
https://i.postimg.cc/gjV4nth9/Chester-Colour-minus-BW.png
That last one looks a lot sharper than what I used to see on a colour TV
when viewing only the colour information (I forget how - I think just
turning the contrast right down did it). That gave you no sharp edges at
all - just very smeary.
In message <u6juna$16m0b$1@dont-email.me> at Sat, 17 Jun 2023 10:28:23,
Brian Gaff <brian1gaff@gmail.com> writes
I know what you mean. Some VCRs tended to smear the chroma and pulsate it >>asI don't remember seeing a pulsating one! Though a multigenerational copy could get horrendous pretty quickly. Chroma _lag_ was common - I think
well.
Brian
most memorably on snooker; one got used to seeing a grey ball, with a
ghostly coloured one to its right, especially in a long shot (where a
fixed chroma offset was of course more noticeable).
My post was really just thinking - if all we have is a digitised copy,
it might be an interesting task how to correct such material, whether
it's chroma lag or lead (presumably both of similar difficulty).
I think the days of retrieving e. g. lost Dr. Who episodes from private copies were mostly still in the analogue days, or at least where the machinery in which the two signals were present was still in use, even
if the actual re-syncing was done digitally. (I think the most
fascinating aspect of that work was when someone realised that black-and-white film copies might still contain the colour subcarrier.)
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf
Madness takes its toll. Please have exact change
[via Penny Mayes (mayes@pmail.net)]
"J. P. Gilliver" <G6JPG@255soft.uk> wrote in message news:MNs1rVg1XZjkFwCi@255soft.uk...
In message <u6juna$16m0b$1@dont-email.me> at Sat, 17 Jun 2023 10:28:23,
Brian Gaff <brian1gaff@gmail.com> writes
I know what you mean. Some VCRs tended to smear the chroma and pulsate it >>>asI don't remember seeing a pulsating one! Though a multigenerational copy
well.
Brian
could get horrendous pretty quickly. Chroma _lag_ was common - I think
most memorably on snooker; one got used to seeing a grey ball, with a
ghostly coloured one to its right, especially in a long shot (where a
fixed chroma offset was of course more noticeable).
My post was really just thinking - if all we have is a digitised copy,
it might be an interesting task how to correct such material, whether
it's chroma lag or lead (presumably both of similar difficulty).
I think the days of retrieving e. g. lost Dr. Who episodes from private
copies were mostly still in the analogue days, or at least where the
machinery in which the two signals were present was still in use, even
if the actual re-syncing was done digitally. (I think the most
fascinating aspect of that work was when someone realised that
black-and-white film copies might still contain the colour subcarrier.)
Digital colour photographs and videos are still stored as luminance and
some form of chrominance difference. And often the colour resolution is
half the luminance resolution in one or both directions, as for analogue video.
It ought to be fairly easy to write a program that shifts the chroma
pixels sideways a bit compared with the luminance.
If you take a still photo (eg a JPEG or PNG) and make a black and white
copy, you can subtract this from the original photo (most image-editing software such as Paint Shop Pro or Photoshop can do this), you can see how blurred the remaining colour info is after you've subtracted the
luminance.
Here's an example: a colour photo of the famous clock on the city wall in Chester, then a black and white version of it and then colour minus BW (adding on 128 to each pixel to avoid "pixels with a negative value"!) leaving just the chroma.
https://i.postimg.cc/7Y1Q6h1C/Chester-Colour.jpg https://i.postimg.cc/1XhJR1fc/Chester-BW.jpg https://i.postimg.cc/gjV4nth9/Chester-Colour-minus-BW.png
Yes the colour definition was much less than the b/we and the brain >compensated for this smear to some extent.[]
I seem to recall the pulsating colour was mainly on the old Philips vcr >systems, of any of the speeds. There were on some colours a static
vertical striping in saturation effect. Seen moor on highly saturated >colours. It looked odd as it was static so when the camera panned it stayed >in the same place.
Some video 8 recordings had the leading colour effect, but as the format
never really caught on a body bothered. Video 2000 of course was known for >its video noise effects.
Vhs standard was crap definition and betamax was good if you used basf or
Fuji tapes on it.
I actually miss video recorders, despite their many moving parts, they
worked surprisingly well.
Brian
I often thought the manufacturers missed a chance by not releasing one
or two models with transparent housings so you could see them working;
OK, most people probably _wouldn't_ want to, but I'd have thought there
would be enough of us that would to justify one or two models. After
all, people love steam trains, and I'm sure that's part of the attraction.
I've just watched a clip (https://www.youtube.com/watch?v=_P09xG1clcg -
no, it wasn't to my taste) where clearly there is a significant time
offset between chroma and luma. It occurred to me that, when nowadays if
the only extant copy is a digitised version (the original analogue
having been lost, or its source unknown), it'd be quite an interesting >challenge to correct it: I don't think there's anything in the digital
domain that's analogous to the luma/chroma split, so presumably the
chroma and luma would have to be regenerated, then slewed back into >approximate alignment.
(This one is slightly unusual in that the chroma appears to _lead_ the
luma rather than the usual lag.)
I always wondered how the later VHS decks were able to maintain a tape library, so that when you inserted a given tape, the deck would display
all the programmes that were recorded on that tape. I realise that the
list was maintained, per tape, in non-volatile memory on the deck, and
was not stored on the tape itself. But how did the deck manage to
distinguish between one tape and another as soon as the tape was
inserted, so as to present the correct tape-contents list? Did all VHS
tapes contain a unique RFID tag, or was there some other way that a
unique tape ID was recorded all the way along the control track?
On 6/18/23 20:52, NY wrote:
<snip>
I always wondered how the later VHS decks were able to maintain a tape
library, so that when you inserted a given tape, the deck would display
all the programmes that were recorded on that tape. I realise that the
list was maintained, per tape, in non-volatile memory on the deck, and
was not stored on the tape itself. But how did the deck manage to
distinguish between one tape and another as soon as the tape was
inserted, so as to present the correct tape-contents list? Did all VHS
tapes contain a unique RFID tag, or was there some other way that a
unique tape ID was recorded all the way along the control track?
Dunno. First I heard of it :)
Panasonic NV-FJ760 Tape Library
https://www.youtube.com/watch?v=TNgaUd2CIfY
https://www.manualslib.com/manual/117527/Panasonic-Nv-Fj710-Series.html?page=26
Control track apparently.
https://en.wikipedia.org/wiki/Control_track
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