1、 Copyright 2015 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved March 26, 2015 Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 2 1 Scope . 3 2 Conformance Notation . 3 3 Terms and Definitions 3 3.1 XYZ
2、 . 3 3.2 XYZ . 3 4 XYZ to YDZDX Computation 4 5 YDZDX to XYZ Computation 4 Annex A Example Digital Representation (Informative) . 5 A.1 Digital Representation . 5 A.2 Code Value Mapping. 5 A.3 Inverse Code Value Mapping 5 Annex B Color-Difference Weighting Coefficients (Informative) 6 B.1 Objective
3、of Weighting Coefficients 6 B.2 Calculation of Weighting Coefficients . 6 Annex C Bibliography (Informative) . 7 Page 1 of 7 pages SMPTE ST 2085:2015 SMPTE STANDARD YDZDX Color-Difference Computations for High Dynamic Range XYZ Signals SMPTE ST 2085:2015 Page 2 of 7 pages Foreword SMPTE (the Society
4、 of Motion Picture and Television Engineers) is an internationally-recognized standards developing organization. Headquartered and incorporated in the United States of America, SMPTE has members in over 80 countries on six continents. SMPTEs Engineering Documents, including Standards, Recommended Pr
5、actices, and Engineering Guidelines, are prepared by SMPTEs Technology Committees. Participation in these Committees is open to all with a bona fide interest in their work. SMPTE cooperates closely with other standards-developing organizations, including ISO, IEC and ITU. SMPTE Engineering Documents
6、 are drafted in accordance with the rules given in its Standards Operations Manual. SMPTE ST 2085 was prepared by Technology Committee 10E. Intellectual Property At the time of publication no notice had been received by SMPTE claiming patent rights essential to the implementation of this Standard. H
7、owever, attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. SMPTE shall not be held responsible for identifying any or all such patent rights. Introduction This section is entirely informative and does not form an integral part of thi
8、s Engineering Document. This standard defines the color-difference computation to be used with high dynamic range XYZ signals. The nonlinear encoding to XYZ affects the optimization of weighting coefficients, as does the selection of a target color for zero color-difference. The coefficients defined
9、 in this document have been optimized for XYZ encoded with the inverse of the EOTF defined in SMPTE ST 2084 to yield zero color-difference for a target of D65 (x,y chromaticity 0.3127, 0.3290, as specified in Section 3.1.1 of SMPTE RP 177) at 500 cd/m2. SMPTE ST 2085:2015 Page 3 of 7 pages 1 Scope T
10、his standard defines YDZDX color-difference computations to be used with high dynamic range XYZ signals. The computations have been optimized for the EOTF specified in SMPTE ST 2084, primarily for use in non-broadcast content. 2 Conformance Notation Normative text is text that describes elements of
11、the design that are indispensable or contains the conformance language keywords: “shall“, “should“, or “may“. Informative text is text that is potentially helpful to the user, but not indispensable, and can be removed, changed, or added editorially without affecting interoperability. Informative tex
12、t does not contain any conformance keywords. All text in this document is, by default, normative, except: the Introduction, any section explicitly labeled as “Informative“ or individual paragraphs that start with “Note:” The keywords “shall“ and “shall not“ indicate requirements strictly to be follo
13、wed in order to conform to the document and from which no deviation is permitted. The keywords, “should“ and “should not“ indicate that, among several possibilities, one is recommended as particularly suitable, without mentioning or excluding others; or that a certain course of action is preferred b
14、ut not necessarily required; or that (in the negative form) a certain possibility or course of action is deprecated but not prohibited. The keywords “may“ and “need not“ indicate courses of action permissible within the limits of the document. The keyword “reserved” indicates a provision that is not
15、 defined at this time, shall not be used, and may be defined in the future. The keyword “forbidden” indicates “reserved” and in addition indicates that the provision will never be defined in the future. A conformant implementation according to this document is one that includes all mandatory provisi
16、ons (“shall“) and, if implemented, all recommended provisions (“should“) as described. A conformant implementation need not implement optional provisions (“may“) and need not implement them as described. Unless otherwise specified, the order of precedence of the types of normative information in thi
17、s document shall be as follows: normative prose shall be the authoritative definition; tables shall be next; followed by formal languages; then figures; and then any other language forms. 3 Terms and Definitions The following terms and definitions are used in this document: 3.1 XYZ The linear tristi
18、mulus values as defined in CIE 1931 standard colorimetric system. 3.2 XYZ XYZ tristimulus values encoded as nonlinear values. SMPTE ST 2085:2015 Page 4 of 7 pages 4 XYZ to YDZDX Computation The luminance component value Y shall be preserved. Color-difference component values DZ and DX shall be compu
19、ted as follows: = 1 2.0 = 22.0 where 1 = 0.986566 2 = 0.991902 DX and DZ are in the range -0.5, 0.5 X, Y and Z are in the range 0.0, 1.0 The coefficients 1 and 2 have been optimized for the target of D65 with the inverse-EOTF specified in SMPTE ST 2084 at 500 cd/m2. Annex B describes the derivation
20、of 1 and 2. DZ and DX may be further quantized for digital representation. An example digital representation can be found in Annex A. 5 YDZDX to XYZ Computation The YDZDX color-difference computation is invertible using its mathematical inverse to compute X, Y and Z. The luminance component value Y
21、shall be preserved. X and Z shall be computed from the YDZDX color-difference values as follows: = 2 + 2 = (2 + )/1 where 1 = 0.986566 2 = 0.991902 DX and DZ are in the range -0.5, 0.5 X, Y and Z are in the range 0.0, 1.0 The coefficients 1 and 2 have been optimized for the target of D65 with the in
22、verse-EOTF specified in SMPTE ST 2084 at 500 cd/m2. Annex B describes the derivation of 1 and 2. SMPTE ST 2085:2015 Page 5 of 7 pages Annex A Example Digital Representation (Informative) A.1 Digital Representation An example digital representation is shown which encodes color-difference values into
23、digital code values. A.2 Code Value Mapping Digital code values are computed as follows: = Floor(876 + 64 + 0.5) = Floor(896 + 512 + 0.5) where Y is the luminance component value in the range 0.0, 1.0 YD is the resulting luminance digital code D is the color-difference component value in the range -
24、0.5, 0.5 DD is the resulting color-difference digital code = 210 is an integer greater than or equal to 10, corresponding to the number of bits per code value The unary function Floor yields the largest integer not greater than its argument. This scaling places the extrema of Y at code words 040h(64
25、) and 3ACh(940) and the extrema of DX and DZ at code words 040h(64) and 3C0h(960) in a 10-bit representation. A.3 Inverse Code Value Mapping Color-difference values are computed from their digital code values as follows: = ( 64 ) (876 ) = ( 512 ) (896 ) where YD is the luminance digital code Y is th
26、e resulting luminance component value in the range 0.0, 1.0 DD is the color-difference digital code D is the resulting color-difference component value in the range -0.5, 0.5 = 210 is an integer greater than or equal to 10, corresponding to the number of bits per code value SMPTE ST 2085:2015 Page 6
27、 of 7 pages Annex B Color-Difference Weighting Coefficients (Informative) B.1 Objective of Weighting Coefficients Color-difference signals are calculated as a weighted difference. The weighting coefficients determine the target color for which the color-difference signal will have zero value. If equ
28、al weighting were utilized, zero color-difference would be aligned with the XYZ equal energy neutral axis. Zero color-difference can be aligned more optimally with the picture content white by adjusting the weighting. The nonlinear encoding of XYZ using the inverse of an EOTF can introduce a curvatu
29、re in the alignment of color-difference values, as is the case for the inverse of the SMPTE ST 2084 EOTF. Therefore the weighting can be optimized for a specific chromaticity and luminance level, such as D65 (x,y chromaticity 0.3127, 0.3290, as specified in Section 3.1.1 of SMPTE RP 177) at 500 cd/m
30、2. B.2 Calculation of Weighting Coefficients The weighting coefficients are dependent on the encoding to XYZ according to an inverse-EOTF. The method takes as its input the XYZ values of the target chromaticity and luminance with zero color-difference. The following steps are used to calculate the c
31、oefficients: Step 1: Intermediate scaling coefficients are computed as follows: = = = (1,1 ) = (1,1 ) Step 2: The color-difference scaling coefficients are computed as follows: = = = = = 0 2 2 2 2 0 For the specified optimization target, the scaling coefficients and evaluate to 1, resulting in the s
32、implified equations of Section 4 and Section 5 with the scaling coefficients 1 and 2 taking the values of and , respectively. SMPTE ST 2085:2015 Page 7 of 7 pages Annex C Bibliography (Informative) CIE S 014-2/E:2006, Colorimetry Part 2: CIE Standard Illuminants ISO 11664-2:2007 SMPTE RP 177-1993, Derivation of Basic Color Television Equations SMPTE ST 2084:2014, High Dynamic Range Electro-Optical Transfer Function of Mastering Reference Displays
