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

Media Data Atom TypesVideo MediaMatrix indexA 16-bit unsigned integer containing an index into a table specifying the transformation matrix coefficientsused to translate between RGB color space values and Y´CbCr values. The table of matrixes specifies thematrix used during the translation, as shown in Figure 4-2 (page 163).The transfer function and matrix are used as shown in Figure 4-2 (page 163).Figure 4-2LightmeasuredbycameracircuitryTransfer between RGB and Y´CbCr color spacesRGBE W' = f(W)E W' = f(W)E W' = f(W)E R'E G'EB'MatrixE Y'E CbE CrNumericalcodinginQuickTimefileNumericalcodinginQuickTimefileE Y'E R'W = g(E W' )E Cr E B'W = g(E W' )E CbMatrix -1 E G'W = g(E W' )RGBDisplaycircuitryemitslightThe Y´CbCr values stored in a file are normalized to a range of [0,1]for Y´ and [-0.5, +0.5] for Cb and Cr whenperforming these operations. The normalized values are then scaled to the proper bit depth for a particularY´CbCr format before storage in the file as shown in Figure 4-3 (page 163).Figure 4-3Normalized values, using the symbol E with a subscript for Y´, Cb, or CrNote The symbols used for these values are not intended to correspond to the use of these samesymbols in other standards. In particular, "E" should not be interpreted as voltage.These normalized values can be mapped onto the stored integer values of a particular compression type's Y´,Cb, and Cr components using two different schemes, which we will call Scheme A and Scheme B.Warning Other, slightly different encoding/mapping schemes exist in the video industry, and dataencoded using these schemes must be converted to one of the QuickTime schemes defined here.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.163