UIT - Secteur de la normalisation des télécommunications
ITU - Telecommunication Standardization Sector
UIT - Sector de Normalización de las Telecomunicaciones
Study Period 2001-2004
16 D.172 (WP 1/16)
Geneva, 5 – 15 February 2002
TITLE: Proposal to start the study of sYCC as the additional color space for color facsimile terminals
1. Background of color space selection for color facsimile terminals
The selection of an optimum color space for color facsimile was addressed (discussed) by ITU-T (formerly CCITT) / SG8 / WP C / Q4 during between 1991 and 1993. At that time, the “input and output” interface for facsimile terminal was limited to get a hard copy, and there was agreement to select a single color space with 8 bits color component for data exchange. These constraints were targeted to deliver desired quality with low cost. These studies resulted in acceptance of CIELAB (1976CIEL*a*b) as the mandatory color space for color facsimile terminals during the May ’93 ITU-T / SG8 Geneva meeting. Color space selection was followed by default illuminant and CIELAB range studies and selection. The ITU-T Recommendation T.42, tilted “continuous tone colour reproduction method for colour facsimile”, was completed in 1996. T.42 referenced as being required for ITU-T Recommendations on color G3/G4 facsimile terminals, such as T.4, T.4Annex E, T.30, T.30 Annex E, T.563, T.521, T.503 Annex B, T.43 and T.44.
2. sYCC as the additional color space
Recently, many color input devices, such as reflectance scanner, film scanner and digital camera, have become popular. In particular, the distribution of the digital data over the network, using YCC color space, has become widespread.
CIELAB is very useful for hard copy; however, it is not as effective for deal with digital camera data. This is due to the conversions required from YCC to CIELAB in the sender and from CIELAB to RGB for display at the receiver. These conversions would add undesirable complexity to color facsimile system that accepts digital camera out as an image source.
It is perceived that the market for color facsimile may be increased, if YCC is available for use in color facsimile as an additional color space. There are several flavours of YCC spaces, however, sYCC, which is under standardisation within IEC, may be the best candidate.
sRGB was standardised in 1998 by IEC, mainly as display color space. sYCC, which is the YCbCr style of sRGB, is under development as IEC 61966-2-1. The expansions of sRGB and sYCC are also under developing in IEC.
sRGB and the YCbCr style of sRGB are used in Exif ver.2.1, which is the standard format for digital camera in Japan.
Japan proposes to start the study of sYCC as an additional color space for color facsimile terminals.
In this study, the following points should be clarified.
Harmonisation with the sYCC standardisation effort in IEC:
- The standardisation in ITU-T should be harmonised with that in IEC.
- Expansions of sRGB and sYCC are also under developing in IEC.
- There should be discussion as to whether these expansions shall be included in the ITU-T Recommendation(s) on color facsimile terminals.
Necessity of Illuminant conversion :
- D65 of sYCC illuminant is different from D50 of ITU CIELAB illuminant.
- There should be discussion as to whether a description of the illuminant conversion method between D50 and D65 is necessary in the ITU-T Recommendation(s) on color facsimile terminals.
Necessity of Gamut Mapping:
- sYCC gamut is different from hard copy gamut.
- There should be discussion as to whether a description of gamut mapping method is necessary in the ITU-T Recommendation(s) on color facsimile terminals.
As an extension, the consideration of the applicability of sYCC to the other devices, like digital camera may be necessary.
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E-mail : Hiroaki.Ikegami@fujixerox.co.jp
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