The Unofficial Colour Recovery Wiki



Welcome to the The Unofficial Colour Recovery Wiki
I have set up this Wiki, not in competition with the official Colour Recovery Working Group Wiki, but to provide an alternative place to record developments in Colour Recovery technology which is independent of any one broadcaster or set of users. I feel this is especially important given that the role of the Working Group is changing from that of 'advancement of technology' to one of gatekeeper for the use of Colour Recovery technology, something with which I am not comfortable.

It also gives me an opportunity to report on developments in my own Colour Recovery process which cannot be recorded on the 'official' Wiki since I no longer have the ability to edit that.

Background Information
During the late 1960s and early 1970s many television programmes were archived by being recorded onto black and white movie film. Such telerecordings were often made from PAL-coded material and, although occasionally filtered out, commonly there is evidence of the colour subcarrier in the form of a fine pattern of stripes over originally-coloured areas of the recorded picture.

In the past such chroma patterning has been regarded as a nuisance, since the viewer sees it as picture detail which wasn't present in the original scene. The scanning and display of the films with the use of PAL equipment can also give rise to problems, since the chroma patterning can be misinterpreted by a PAL decoder as a real chrominance signal and result in flashing or rainbow-coloured interference.

More recently it has been realised that it might be possible to use the recorded chroma patterning to recover the missing colour information, either directly or to assist a separate process of colourisation. Thus a full-colour version of a programme could be restored despite the absence of any conventional colour recording.

During 2008 the first practical realisations of a Colour Recovery process were achieved, under the auspices of the Working Group. The main players in these developments were Andrew Browne, who was probably the first to recover any true colour from the chroma patterning in a Film Recording, Andrew Steer, who developed the first working intra-frame process (although it was only able to recover one quadrant of the colour space) and Richard Russell who finally cracked the problem of recovering the full gamut of colours.

Contents
Richard Russell's early experiments
 * A diary of preliminary experiments in 'single quadrant colour recovery'.

Full gamut colour recovery

Full gamut colour recovery (continued)

Full gamut colour recovery (yet more)
 * A chronological record of the work that culminated in successful 'full gamut colour recovery'.

How colour recovery works
 * A technical, but non-mathematical, explanation of Richard Russell's colour recovery process.

Limitations of the process
 * A discussion of the main reasons why the existing colour recovery process can fail.

Ongoing developments
 * An account of developments in the technology of colour recovery.

Process noise spectra
 * 2-dimensional spectra of various internal signals when fed with white noise.

Processed programmes
 * A list of full-length programmes which have undergone the colour recovery process.

Response curves
 * Response curves of the main digital filters used in Richard Russell's colour recovery process.

Software versions
 * A list of the major versions of Richard Russell's Colour Recovery software application, including download and installation information.

Source file specification
 * A detailed specification of the input file format used by Richard Russell's Colour Recovery software.

Spectra of film recordings
 * Some plots of 2D spectra, showing how the levels of the chrominance signals vary and giving some indication of geometric distortion.

Tools and utilities
 * Descriptions of the software tools which have been developed to support the Colour Recovery application.

Latest activity




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