digital archeology, finding traces in the bits

in

This

article in Guardian
today is describing a method of restoring colour to

some original BBC tv shows whose master tapes were wiped in a purge of the

BBC archives.

The shows were originally made in colour, then the master tapes were

destroyed to make more room in the BBC archive, however black and white

copies were made for distribution to countries which didn't have colour TV

capability. The black and white versions were on a smaller format (16 mm)

and of a lower resolution.



The method of recording was the following, the colour shows were displayed

on a large screen and this was re-recorded onto the 16mm tape.



During this process owing to an artifact from the colour, on the black and

white film there is a speckled fingeing error.



It describes this problem in the article as follows: "However, there is a

more relevant problem. Any black and white telerecording of a colour

programme is prone to pick up interference from the colour encoded video

signal. This manifests itself as a pattern of small grey dots, called

chroma-dots, across the picture."



A filter used in the re-recording process could eliminate this error, but at

the time of the recordings the error was considered so minor that often the

filter was omitted. Back then TV was throwaway and space in a basement was

considered more valuable than any idea of cultural heritage. Now we look

back at the decision to scrap the original recordings as somwhat akin to the

burning of the library of Alexandria. Storage, especially digital, is

bountiful.



However, owing to what was then considered to be noise, an error, an

imperfection in the process, James Insell has devised a technique to map

back from these chroma-dots to the original colour. And so by looking at the

finest structure of the current artifact through HD recordings of the 16mm

film we can recapture a state of the past that might have been lost to us.



Digging in the digital detritus has uncovered gold.



The formats of our cultural heritage are changing, and there is ever the

danger that we might loose large chunks of our past when the ability read a

certain format disappears. For specialist cases, such as the BBC archive,

there will be, for some time to come, the likes of James Insell who will be

willing to do the archeology needed to reconstruct from the remnants, but

looking at the growing sprawl of media in my home I have a number of digital

cards that can't be read any more, a zip drive that may or may not contain

code from a summer of astrophysics, and some very personal movies on

betamax, that lie in their boxes, becoming more tomb-like as the years roll

by.



Aside from the personal onus to maintain my own history, I was really

excited by this guardian article. I loved the idea of recovery from

the minutia. It is an interesting example for the need for losses

compression techniques.


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