Colour recovery

Colour recovery (or colour restoration) is a process which can restore lost colour, specifically to television programmes which were originally transmitted in colour, but for which only black & white copies remain archived. Not to be confused with colourisation, colour recovery is a newer process and is fundamentally different from colourisation for several reasons. Firstly, colour recovery can only be performed if the originally transmitted colour signal can be reconstructed or recovered from some source, whereas this is not usually the case for traditional colourisation. Secondly, colourisation can be used to colourise films and programmes that were made in black and white, using still colour photos and/or some educated guesswork to manually choose a colour palette. Conversely, the goal of colour recovery is to reinstate (as closely as possible) the colour signals of programmes originally made in colour as they were first seen. Colour recovery reconstructs the colour information from actual recovered signals and theoretically without depending on guesswork. As of 2010, colour recovery has successfully been applied to episodes of the BBC TV programmes Doctor Who,Dad's Army, and Are You Being Served?.

Due to the well-documented practice of wiping, many original videotape recordings of colour programmes were lost. However, in the case of the BBC, many telerecorded black & white film copies of affected programmes survived. These black & white copies were made for overseas commercial exploitation of BBC programmes. For a variety of technical and practical reasons (for example various incompatible international TV standards, and the then-high cost of videotape over that of film), black & white film copies were the preferred medium for selling programmes overseas. This practice ultimately led to many programmes which were originally made and transmitted in colour only existing in black and white form after the practise of wiping finally ceased.

During the 1970s, various off-air NTSC video-recordings were made by American and Canadian Doctor Who fans, which were later returned to the BBC. Whilst the quality of these early domestic video recordings was not suitable for broadcast, the lower-definition chrominance signal could be retrieved from them. This signal could be successfully combined with the luminance signal from digitally-scanned existing broadcast-quality monochrome telerecordings to make new colour master copies, suitable for broadcast and sales. In the 1990s this method was carried out by the Doctor Who Restoration Team. Several colour-restored Doctor Who serials were subsequently released on VHS. Combining the video-recorded colour signals with the monochrome telerecordings is a non-trivial task, requiring digital processing (for example matching up the different screen sizes of the two recordings). Thus, it wasn't until the early 1990s that cheaply available, sufficiently powerful computer hardware and software made this task particularly practical at that time.

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