Colour recovery
Encyclopedia
Colour recovery 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 Conversely, the goal of colour recovery is to reinstate (as closely as possible) the colour signals of programmes originally made in colour as they were first seen.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?
.
, many original videotape copies 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 This practice ultimately led to many programmes which were originally made and transmitted in colour only existing in black and white form after the regime of wiping finally ceased.
video-recordings were made by American and Canadian Doctor Who fans and 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
. Later, an improved process of converting NTSC colour back to PAL
known as Reverse Standards Conversion
was used, improving the picture quality of colour-restored episodes even further. Amongst others, in 2005, The Claws of Axos
was released on DVD having undergone this improved process. 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.
on a fixed frequency, known as the colour subcarrier. Black and white televisions do not decode this extra colour information in the subcarrier
, using only the luminance to provide a monochrome picture. However, due to limited bandwidth in the video channel, the chrominance and luminance signals bleed into each other considerably, resulting in the colour information showing up visibly as Chroma Crawl
, or Chroma dots
on black & white TV sets. This is normally considered a nuisance in analogue broadcasting. However, since telerecordings were made from black & white TV screens and technicians at the time often decided not to apply a filter to remove this interference, these patterns are retained even in the existing monochrome film prints and theoretically contain the original colour information. (Occasionally the colour information was filtered out using a notch filter and is lost.) The idea to recover this information was originally suggested by BBC researcher, James Insell.
In practice however, the recovery of this colour information from telerecordings is highly complex for several reasons. Firstly, the colour reference timing signal, known as the colour burst, is absent from telerecordings, as it is nominally off the edge of the visible screen area being recorded. This timing has to effectively be recovered since the phase of the chroma dots, which is represented by their horizontal position on the screen, determines the hue of the reconstructed colours. Distortions in the geometry of the telerecordings due to the nature of physically recording from a non-flat CRT screen onto film means that a transformation has to be applied in order to infer the original positions of the chroma dots within the broadcast.
However, these technical obstacles were finally overcome in 2008, and software written by developer Richard Russell
at the informal Colour Recovery Working Group was put to use, finally resulting in the broadcast and release of colour-recovered episodes of Dad's Army and Doctor Who.
Film colorization
Film colorization is any process that adds color to black-and-white, sepia or monochrome moving-picture images. It may be done as a special effect, or to modernize black-and-white films, or to restore color films...
, 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
Doctor Who
Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...
, Dad's Army
Dad's Army
Dad's Army is a British sitcom about the Home Guard during the Second World War. It was written by Jimmy Perry and David Croft and broadcast on BBC television between 1968 and 1977. The series ran for 9 series and 80 episodes in total, plus a radio series, a feature film and a stage show...
and Are You Being Served?
Are You Being Served?
Are You Being Served? is a British sitcom broadcast from 1972 to 1985. It was set in the ladies' and gentlemen's clothing departments of Grace Brothers, a large, fictional London department store. It was written mainly by Jeremy Lloyd and David Croft, with contributions by Michael Knowles and John...
.
Background
Due to the well-documented practice of wipingWiping
Wiping or junking is a colloquial term for action taken by radio and television production and broadcasting companies, in which old audiotapes, videotapes, and telerecordings , are erased, reused, or destroyed after several uses...
, many original videotape copies of colour programmes were lost. However, in the case of the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
, 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 regime of wiping finally ceased.
From off-air recordings
During the 1970s, various off-air NTSCNTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
video-recordings were made by American and Canadian Doctor Who fans and returned to the BBC. Whilst the quality of these early domestic video recordings was not suitable for broadcast, the lower-definition chrominance
Chrominance
Chrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal . Chrominance is usually represented as two color-difference components: U = B' − Y' and V = R' − Y'...
signal could be retrieved from them. This signal could be successfully combined with the luminance
Luma (video)
In video, luma, sometimes called luminance, represents the brightness in an image . Luma is typically paired with chrominance. Luma represents the achromatic image without any color, while the chroma components represent the color information...
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
Doctor Who Restoration Team
The Doctor Who Restoration Team is a loose collection of Doctor Who fans, many within the television industry, who restore Doctor Who episodes for release on DVD....
. Several colour-restored Doctor Who serials were subsequently released on VHS
VHS
The Video Home System is a consumer-level analog recording videocassette standard developed by Victor Company of Japan ....
. Later, an improved process of converting NTSC colour back to PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
known as Reverse Standards Conversion
Reverse Standards Conversion
Reverse Standards Conversion or RSC is a process developed by a team led by James Insell at the BBC for the restoration of video recordings which have already been converted between different video standards using early conversion techniques....
was used, improving the picture quality of colour-restored episodes even further. Amongst others, in 2005, The Claws of Axos
The Claws of Axos
-Writing:In late 1969, script editor Terrance Dicks contacted new writing duo Bob Baker and Dave Martin after reading a draft script they had sent around the BBC for another production, A Man's Life. After offering the duo a seven-part story in November 1969 for Doctor Whos eighth season, Baker and...
was released on DVD having undergone this improved process. 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.
From chroma crawl
Black & white TV systems predate colour, and so subsequent analogue colour broadcast systems have been designed with backwards-compatibility in mind (known as a compatible colour system). Thus, the chrominance (colour) signal is typically 'shoe-horned' into the same channel as the luminance (brightness) signal, modulatedModulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
on a fixed frequency, known as the colour subcarrier. Black and white televisions do not decode this extra colour information in the subcarrier
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
, using only the luminance to provide a monochrome picture. However, due to limited bandwidth in the video channel, the chrominance and luminance signals bleed into each other considerably, resulting in the colour information showing up visibly as Chroma Crawl
Dot crawl
Dot crawl is the popular name for a visual defect of color analog video standards when signals are transmitted as composite video, as in terrestrial broadcast television. It consists of animated checkerboard patterns which appear along vertical color transitions...
, or Chroma dots
Chroma dots
Chroma dots are visual artefacts caused by displaying an unfiltered analogue colour video signal on a black and white television or monitor. They are commonly found on black and white recordings of television programmes originally made in colour...
on black & white TV sets. This is normally considered a nuisance in analogue broadcasting. However, since telerecordings were made from black & white TV screens and technicians at the time often decided not to apply a filter to remove this interference, these patterns are retained even in the existing monochrome film prints and theoretically contain the original colour information. (Occasionally the colour information was filtered out using a notch filter and is lost.) The idea to recover this information was originally suggested by BBC researcher, James Insell.
In practice however, the recovery of this colour information from telerecordings is highly complex for several reasons. Firstly, the colour reference timing signal, known as the colour burst, is absent from telerecordings, as it is nominally off the edge of the visible screen area being recorded. This timing has to effectively be recovered since the phase of the chroma dots, which is represented by their horizontal position on the screen, determines the hue of the reconstructed colours. Distortions in the geometry of the telerecordings due to the nature of physically recording from a non-flat CRT screen onto film means that a transformation has to be applied in order to infer the original positions of the chroma dots within the broadcast.
However, these technical obstacles were finally overcome in 2008, and software written by developer Richard Russell
Richard T. Russell
Richard Thomas Russell is the creator of the BBC Basic for Windows programming language and the author of the Z80 and MS-DOS versions of BBC BASIC....
at the informal Colour Recovery Working Group was put to use, finally resulting in the broadcast and release of colour-recovered episodes of Dad's Army and Doctor Who.