ANSI/NIST-ITL 1-2011 - NIST Visual Image Processing Group ...
ANSI/NIST-ITL 1-2011 - NIST Visual Image Processing Group ... ANSI/NIST-ITL 1-2011 - NIST Visual Image Processing Group ...
ANSI/NIST-ITL 1-2011Data Format for the Interchange of Biometric and Forensic InformationTable 1 Color spacesCode DescriptionUNK UndefinedGRAY Grayscale (monochrome)RGB Undetermined color space for an RGB imageSRGB sRGB (IEC 61966-2-1)YCC YCbCr (legacy)SYCC YCbCr (JPEG 2000 compressed)4.5.1 Backwards compatibility of color spaceIn versions of this standard prior to 2007, the term “color space” referred todevice-dependent color information with a particular sequence and range for thethree color channels. The choice was either RGB or an RGB-derivative spaceknown as YCC. Neither space provides an objective definition of a particularcolor or relates to the way in which humans perceive color.Although sRGB is the preferred color space for compressed images for thisversion, in the 2000 version of this standard, it was stated that “the preferredcolor space for compressed images using baseline JPEG and JFIF is YCbCr tobe coded as ‛YCC’,” while the color space for uncompressed color images was tobe labeled RGB. Therefore, for backwards compatibility purposes, new systemsshall accommodate JPEG images that have been labeled as using the YCC colorspace. Specifically, systems conformant with this standard shall accept an entryof YCC and interpret it as meaning a (device-dependent) RGB color space.4.5.2 Color space sRGBTo ensure that color images exchanged between differing systems can becorrectly displayed or printed, images should be converted to the deviceindependentcolor space, sRGB 6 , before compression or transmission to anothersystem. As defined by IEC 61966-2-1, sRGB is a non-linear display profile thataccommodates the voltage-to-color response characteristics of most high quality6 For information on sRGB, see http://www.w3.org/Graphics/Color/sRGB or many of the white papers available athttp://www.color.org.•6DRAFT 2
ANSI/NIST-ITL 1-2011Data Format for the Interchange of Biometric and Forensic InformationCRT monitors. The colors of the red, green, and blue phosphors (primaries) andthe white point setting of an sRGB-conformant monitor are specified in the IECdocument.The relationship between sRGB and a linear RGB space having the IEC-definedprimaries and white point is as follows:valuesRGB⎧12.92valuelin,for valuelin≤ 0.0031308= ⎨( 1/2.4 )⎩1055. valuelin− 0.055,for valuelin> 0.0031308where value is an R, G, or B value in linear RGB spacelin(with a range of0 to1) andR, G, or B value in non - linearrange of 0 to1). To convert from/to the range of 0 to 255,divide/multiply by 255.valuesRGBis the correspondingsRGB space (also with aTypically, modern digital cameras, desktop scanners, LCD monitors, andprinters, although they do not inherently operate in sRGB space, are designedwith circuitry or software to produce sRGB output or to accommodate sRGB asan input space. If an image acquisition device's color space is unknown, sRGBis usually a reasonable choice. If an acquisition device and its software cannotprovide sRGB output, various color management products are availablecommercially that use its color profile, often available from its manufacturer, toconvert images in its native color space to sRGB.4.6 Compression algorithmsCompressed image data shall adhere to the requirements of the algorithm used.Table 2 lists the binary (shown here in base 10 and used only in Record Type-4)and ASCII codes to be used for the available compression methods for encodinggrayscale and color images described by this standard. The type of data beingexchanged (fingerprint, face, etc.) limits the choice of compression algorithms.The description for each type of data exchange lists the legitimate compressionalgorithms that can be used for that type.Brad Wing 6/19/10 5:07 PMComment: Note the removal of the section onbinary compression algorithms since RecordTypes 3, 5, and 6 are deprecated.Brad Wing 6/19/10 5:07 PMComment: Clarification that the first column isonly applicable to Record Type-4.Table 2 Grayscale & color image compression codesAlgorithm NameBinaryCode(InBase 10)ASCIICodeUncompressed 0 NONE7DRAFT 2
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<strong>ANSI</strong>/<strong>NIST</strong>-<strong>ITL</strong> 1-<strong>2011</strong>Data Format for the Interchange of Biometric and Forensic InformationTable 1 Color spacesCode DescriptionUNK UndefinedGRAY Grayscale (monochrome)RGB Undetermined color space for an RGB imageSRGB sRGB (IEC 61966-2-1)YCC YCbCr (legacy)SYCC YCbCr (JPEG 2000 compressed)4.5.1 Backwards compatibility of color spaceIn versions of this standard prior to 2007, the term “color space” referred todevice-dependent color information with a particular sequence and range for thethree color channels. The choice was either RGB or an RGB-derivative spaceknown as YCC. Neither space provides an objective definition of a particularcolor or relates to the way in which humans perceive color.Although sRGB is the preferred color space for compressed images for thisversion, in the 2000 version of this standard, it was stated that “the preferredcolor space for compressed images using baseline JPEG and JFIF is YCbCr tobe coded as ‛YCC’,” while the color space for uncompressed color images was tobe labeled RGB. Therefore, for backwards compatibility purposes, new systemsshall accommodate JPEG images that have been labeled as using the YCC colorspace. Specifically, systems conformant with this standard shall accept an entryof YCC and interpret it as meaning a (device-dependent) RGB color space.4.5.2 Color space sRGBTo ensure that color images exchanged between differing systems can becorrectly displayed or printed, images should be converted to the deviceindependentcolor space, sRGB 6 , before compression or transmission to anothersystem. As defined by IEC 61966-2-1, sRGB is a non-linear display profile thataccommodates the voltage-to-color response characteristics of most high quality6 For information on sRGB, see http://www.w3.org/Graphics/Color/sRGB or many of the white papers available athttp://www.color.org.•6DRAFT 2
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