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06f084468e
The existing av_csp_trc_func_from_id() mostly implements the OETF, except for PQ. As such, we are currently missing a precise definition of an ITU-R EOTF. Introduce the new functions av_csp_itu_eotf() and av_csp_itu_eotf_inv(), to fill this void. Note that this is not possible in all cases, e.g. AVCOL_TRC_LOG which has no corresponding EOTF definition in any ITU-R standard. Note that we cannot implement the proper HLG and SMPTE 428 OOTFs without access to all three color channels, because they are not independent per channel. As a result, we need to define them on double[3] instead of double (*func)(double).
193 lines
6.5 KiB
C
193 lines
6.5 KiB
C
/*
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* Copyright (c) 2015 Kevin Wheatley <kevin.j.wheatley@gmail.com>
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* Copyright (c) 2016 Ronald S. Bultje <rsbultje@gmail.com>
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* Copyright (c) 2023 Leo Izen <leo.izen@gmail.com>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef AVUTIL_CSP_H
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#define AVUTIL_CSP_H
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#include "pixfmt.h"
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#include "rational.h"
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/**
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* @file
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* Colorspace value utility functions for libavutil.
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* @ingroup lavu_math_csp
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* @author Ronald S. Bultje <rsbultje@gmail.com>
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* @author Leo Izen <leo.izen@gmail.com>
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* @author Kevin Wheatley <kevin.j.wheatley@gmail.com>
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*/
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/**
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* @defgroup lavu_math_csp Colorspace Utility
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* @ingroup lavu_math
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* @{
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*/
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/**
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* Struct containing luma coefficients to be used for RGB to YUV/YCoCg, or similar
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* calculations.
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*/
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typedef struct AVLumaCoefficients {
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AVRational cr, cg, cb;
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} AVLumaCoefficients;
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/**
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* Struct containing chromaticity x and y values for the standard CIE 1931
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* chromaticity definition.
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*/
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typedef struct AVCIExy {
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AVRational x, y;
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} AVCIExy;
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/**
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* Struct defining the red, green, and blue primary locations in terms of CIE
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* 1931 chromaticity x and y.
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*/
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typedef struct AVPrimaryCoefficients {
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AVCIExy r, g, b;
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} AVPrimaryCoefficients;
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/**
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* Struct defining white point location in terms of CIE 1931 chromaticity x
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* and y.
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*/
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typedef AVCIExy AVWhitepointCoefficients;
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/**
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* Struct that contains both white point location and primaries location, providing
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* the complete description of a color gamut.
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*/
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typedef struct AVColorPrimariesDesc {
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AVWhitepointCoefficients wp;
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AVPrimaryCoefficients prim;
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} AVColorPrimariesDesc;
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/**
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* Function pointer representing a double -> double transfer function that
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* performs either an OETF transfer function, or alternatively an inverse EOTF
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* function (in particular, for SMPTE ST 2084 / PQ). This function inputs
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* linear light, and outputs gamma encoded light.
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*
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* See ITU-T H.273 for more information.
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*/
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typedef double (*av_csp_trc_function)(double);
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/**
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* Retrieves the Luma coefficients necessary to construct a conversion matrix
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* from an enum constant describing the colorspace.
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* @param csp An enum constant indicating YUV or similar colorspace.
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* @return The Luma coefficients associated with that colorspace, or NULL
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* if the constant is unknown to libavutil.
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*/
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const AVLumaCoefficients *av_csp_luma_coeffs_from_avcsp(enum AVColorSpace csp);
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/**
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* Retrieves a complete gamut description from an enum constant describing the
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* color primaries.
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* @param prm An enum constant indicating primaries
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* @return A description of the colorspace gamut associated with that enum
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* constant, or NULL if the constant is unknown to libavutil.
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*/
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const AVColorPrimariesDesc *av_csp_primaries_desc_from_id(enum AVColorPrimaries prm);
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/**
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* Detects which enum AVColorPrimaries constant corresponds to the given complete
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* gamut description.
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* @see enum AVColorPrimaries
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* @param prm A description of the colorspace gamut
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* @return The enum constant associated with this gamut, or
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* AVCOL_PRI_UNSPECIFIED if no clear match can be idenitified.
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*/
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enum AVColorPrimaries av_csp_primaries_id_from_desc(const AVColorPrimariesDesc *prm);
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/**
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* Determine a suitable 'gamma' value to match the supplied
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* AVColorTransferCharacteristic.
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*
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* See Apple Technical Note TN2257 (https://developer.apple.com/library/mac/technotes/tn2257/_index.html)
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*
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* This function returns the gamma exponent for the OETF. For example, sRGB is approximated
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* by gamma 2.2, not by gamma 0.45455.
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*
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* @return Will return an approximation to the simple gamma function matching
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* the supplied Transfer Characteristic, Will return 0.0 for any
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* we cannot reasonably match against.
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*/
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double av_csp_approximate_trc_gamma(enum AVColorTransferCharacteristic trc);
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/**
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* Determine the function needed to apply the given
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* AVColorTransferCharacteristic to linear input.
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*
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* The function returned should expect a nominal domain and range of [0.0-1.0]
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* values outside of this range maybe valid depending on the chosen
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* characteristic function.
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*
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* @return Will return pointer to the function matching the
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* supplied Transfer Characteristic. If unspecified will
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* return NULL:
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*/
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av_csp_trc_function av_csp_trc_func_from_id(enum AVColorTransferCharacteristic trc);
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/**
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* Returns the mathematical inverse of the corresponding TRC function.
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*/
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av_csp_trc_function av_csp_trc_func_inv_from_id(enum AVColorTransferCharacteristic trc);
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/**
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* Function pointer representing an ITU EOTF transfer for a given reference
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* display configuration.
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*
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* @param Lw The white point luminance of the display, in nits (cd/m^2).
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* @param Lb The black point luminance of the display, in nits (cd/m^2).
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*/
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typedef void (*av_csp_eotf_function)(double Lw, double Lb, double c[3]);
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/**
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* Returns the ITU EOTF corresponding to a given TRC. This converts from the
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* signal level [0,1] to the raw output display luminance in nits (cd/m^2).
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* This is done per channel in RGB space, except for AVCOL_TRC_SMPTE428, which
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* assumes CIE XYZ in- and output.
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*
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* @return A pointer to the function implementing the given TRC, or NULL if no
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* such function is defined.
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*
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* @note In general, the resulting function is defined (wherever possible) for
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* out-of-range values, even though these values do not have a physical
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* meaning on the given display. Users should clamp inputs (or outputs)
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* if this behavior is not desired.
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*
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* This is also the case for functions like PQ, which are defined over an
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* absolute signal range independent of the target display capabilities.
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*/
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av_csp_eotf_function av_csp_itu_eotf(enum AVColorTransferCharacteristic trc);
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/**
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* Returns the mathematical inverse of the corresponding EOTF.
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*/
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av_csp_eotf_function av_csp_itu_eotf_inv(enum AVColorTransferCharacteristic trc);
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/**
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* @}
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*/
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#endif /* AVUTIL_CSP_H */
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