Quicktime File Format (2012-08-14).pdf

Media Data Atom TypesVideo MediaThe 'colr' atom contains four fields: a color parameter type and three indexes. The indexes are to a table ofprimaries, a table of transfer function coefficients, and a table of matrixes.Figure 4-1 (page 162) shows the layout of this atom.Figure 4-1The layout of a color atomBytesColor atomAtom sizeType = 'colr'44Color parameter type = 'nclc' 4Primaries index = 1 2Transfer function index = 1 2Matrix index = 12The table of matrixes specifies the matrix used during the translation, as shown in Figure 4-2 (page 163).Color parameter typeA 32-bit field containing a four-character code for the color parameter type. The currently defined typesare 'nclc' for video, and 'prof' for print. The color parameter type distinguishes between print andvideo mappings.If the color parameter type is 'prof', then this field is followed by an ICC profile. This is the color modelused by Apple’s ColorSync. The contents of this type are not defined in this document. Contact AppleComputer for more information on the 'prof' type 'colr' extension.If the color parameter type is 'nclc' then this atom contains the following fields:Primaries indexA 16-bit unsigned integer containing an index into a table specifying the CIE 1931 xy chromaticitycoordinates of the white point and the red, green, and blue primaries. The table of primaries specifiesthe white point and the red, green, and blue primary color points for a video system.Transfer function indexA 16-bit unsigned integer containing an index into a table specifying the nonlinear transfer functioncoefficients used to translate between RGB color space values and Y´CbCr values. The table of transferfunction coefficients specifies the nonlinear function coefficients used to translate between the storedY´CbCr values and a video capture or display system, as shown in Figure 4-2 (page 163).2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.162