From 06f084468e034ecb0bfbe522953c1efd77595454 Mon Sep 17 00:00:00 2001 From: Niklas Haas Date: Mon, 25 Nov 2024 13:52:30 +0100 Subject: [PATCH] avutil/csp: add EOTF function definitions 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). --- doc/APIchanges | 3 + libavutil/csp.c | 205 ++++++++++++++++++++++++++++++++++++++++++++ libavutil/csp.h | 33 +++++++ libavutil/version.h | 2 +- 4 files changed, 242 insertions(+), 1 deletion(-) diff --git a/doc/APIchanges b/doc/APIchanges index cdd2afb851..b9af3de933 100644 --- a/doc/APIchanges +++ b/doc/APIchanges @@ -2,6 +2,9 @@ The last version increases of all libraries were on 2024-03-07 API changes, most recent first: +2024-12-05 - xxxxxxxxxx - lavu 59.49.100 - csp.h + Add av_csp_itu_eotf() and av_csp_itu_eotf_inv(). + 2024-12-05 - xxxxxxxxxx - lavu 59.48.100 - csp.h Add av_csp_trc_func_inv_from_id(). diff --git a/libavutil/csp.c b/libavutil/csp.c index fe45c611dd..d69599f513 100644 --- a/libavutil/csp.c +++ b/libavutil/csp.c @@ -429,3 +429,208 @@ av_csp_trc_function av_csp_trc_func_inv_from_id(enum AVColorTransferCharacterist return NULL; return trc_inv_funcs[trc]; } + +static void eotf_linear(const double Lw, const double Lb, double E[3]) +{ + for (int i = 0; i < 3; i++) + E[i] = (Lw - Lb) * E[i] + Lb; +} + +static void eotf_linear_inv(const double Lw, const double Lb, double L[3]) +{ + for (int i = 0; i < 3; i++) + L[i] = (L[i] - Lb) / (Lw - Lb); +} + +#define WRAP_SDR_OETF(name) \ +static void oetf_##name(double L[3]) \ +{ \ + for (int i = 0; i < 3; i++) \ + L[i] = trc_##name(L[i]); \ +} \ + \ +static void oetf_##name##_inv(double E[3]) \ +{ \ + for (int i = 0; i < 3; i++) \ + E[i] = trc_##name##_inv(E[i]); \ +} + +WRAP_SDR_OETF(gamma22) +WRAP_SDR_OETF(gamma28) +WRAP_SDR_OETF(iec61966_2_1) + +#define WRAP_SDR_EOTF(name) \ +static void eotf_##name(double Lw, double Lb, double E[3]) \ +{ \ + oetf_##name##_inv(E); \ + eotf_linear(Lw, Lb, E); \ +} \ + \ +static void eotf_##name##_inv(double Lw, double Lb, double L[3]) \ +{ \ + eotf_linear_inv(Lw, Lb, L); \ + oetf_##name(L); \ +} + +WRAP_SDR_EOTF(gamma22) +WRAP_SDR_EOTF(gamma28) +WRAP_SDR_EOTF(iec61966_2_1) + +static void eotf_bt1886(const double Lw, const double Lb, double E[3]) +{ + const double Lw_inv = pow(Lw, 1.0 / 2.4); + const double Lb_inv = pow(Lb, 1.0 / 2.4); + const double a = pow(Lw_inv - Lb_inv, 2.4); + const double b = Lb_inv / (Lw_inv - Lb_inv); + + for (int i = 0; i < 3; i++) + E[i] = (-b > E[i]) ? 0.0 : a * pow(E[i] + b, 2.4); +} + +static void eotf_bt1886_inv(const double Lw, const double Lb, double L[3]) +{ + const double Lw_inv = pow(Lw, 1.0 / 2.4); + const double Lb_inv = pow(Lb, 1.0 / 2.4); + const double a = pow(Lw_inv - Lb_inv, 2.4); + const double b = Lb_inv / (Lw_inv - Lb_inv); + + for (int i = 0; i < 3; i++) + L[i] = (0.0 > L[i]) ? 0.0 : pow(L[i] / a, 1.0 / 2.4) - b; +} + +static void eotf_smpte_st2084(const double Lw, const double Lb, double E[3]) +{ + for (int i = 0; i < 3; i++) + E[i] = trc_smpte_st2084_inv(E[i]); +} + +static void eotf_smpte_st2084_inv(const double Lw, const double Lb, double L[3]) +{ + for (int i = 0; i < 3; i++) + L[i] = trc_smpte_st2084(L[i]); +} + +/* This implementation assumes an SMPTE RP 431-2 reference projector (DCI) */ +#define DCI_L 48.00 +#define DCI_P 52.37 +#define DCI_X (42.94 / DCI_L) +#define DCI_Z (45.82 / DCI_L) + +static void eotf_smpte_st428_1(const double Lw_Y, const double Lb_Y, double E[3]) +{ + const double Lw[3] = { DCI_X * Lw_Y, Lw_Y, DCI_Z * Lw_Y }; + const double Lb[3] = { DCI_X * Lb_Y, Lb_Y, DCI_Z * Lb_Y }; + + for (int i = 0; i < 3; i++) { + E[i] = (0.0 > E[i]) ? 0.0 : pow(E[i], 2.6) * DCI_P / DCI_L; + E[i] = E[i] * (Lw[i] - Lb[i]) + Lb[i]; + } +} + +static void eotf_smpte_st428_1_inv(const double Lw_Y, const double Lb_Y, double L[3]) +{ + const double Lw[3] = { DCI_X * Lw_Y, Lw_Y, DCI_Z * Lw_Y }; + const double Lb[3] = { DCI_X * Lb_Y, Lb_Y, DCI_Z * Lb_Y }; + + for (int i = 0; i < 3; i++) { + L[i] = (L[i] - Lb[i]) / (Lw[i] - Lb[i]); + L[i] = (0.0 > L[i]) ? 0.0 : pow(L[i] * DCI_L / DCI_P, 1.0 / 2.6); + } +} + +static void eotf_arib_std_b67(const double Lw, const double Lb, double E[3]) +{ + const double gamma = fmax(1.2 + 0.42 * log10(Lw / 1000.0), 1.0); + + /** + * Note: This equation is technically only accurate if the contrast ratio + * Lw:Lb is greater than 12:1; otherwise we would need to use a different, + * significantly more complicated solution. Ignore this as a highly + * degenerate case, since any real world reference display will have a + * static contrast ratio multiple orders of magnitude higher. + */ + const double beta = sqrt(3 * pow(Lb / Lw, 1.0 / gamma)); + double luma; + + for (int i = 0; i < 3; i++) + E[i] = trc_arib_std_b67_inv((1 - beta) * E[i] + beta); + + luma = 0.2627 * E[0] + 0.6780 * E[1] + 0.0593 * E[2]; + luma = pow(fmax(luma, 0.0), gamma - 1.0); + for (int i = 0; i < 3; i++) + E[i] *= Lw * luma; +} + +static void eotf_arib_std_b67_inv(const double Lw, const double Lb, double L[3]) +{ + const double gamma = fmax(1.2 + 0.42 * log10(Lw / 1000.0), 1.0); + const double beta = sqrt(3 * pow(Lb / Lw, 1 / gamma)); + double luma = 0.2627 * L[0] + 0.6780 * L[1] + 0.0593 * L[2]; + + if (luma > 0.0) { + luma = pow(luma / Lw, (1 - gamma) / gamma); + for (int i = 0; i < 3; i++) + L[i] *= luma / Lw; + } else { + L[0] = L[1] = L[2] = 0.0; + } + + for (int i = 0; i < 3; i++) + L[i] = (trc_arib_std_b67(L[i]) - beta) / (1 - beta); +} + +static const av_csp_eotf_function eotf_funcs[AVCOL_TRC_NB] = { + [AVCOL_TRC_BT709] = eotf_bt1886, + [AVCOL_TRC_GAMMA22] = eotf_gamma22, + [AVCOL_TRC_GAMMA28] = eotf_gamma28, + [AVCOL_TRC_SMPTE170M] = eotf_bt1886, + [AVCOL_TRC_SMPTE240M] = eotf_bt1886, + [AVCOL_TRC_LINEAR] = eotf_linear, + /* There is no EOTF associated with these logarithmic encodings, since they + * are defined purely for transmission of scene referred data. */ + [AVCOL_TRC_LOG] = NULL, + [AVCOL_TRC_LOG_SQRT] = NULL, + /* BT.1886 is already defined for values below 0.0, as far as physically + * meaningful, so we can directly use it for extended range encodings */ + [AVCOL_TRC_IEC61966_2_4] = eotf_bt1886, + [AVCOL_TRC_BT1361_ECG] = eotf_bt1886, + [AVCOL_TRC_IEC61966_2_1] = eotf_iec61966_2_1, + [AVCOL_TRC_BT2020_10] = eotf_bt1886, + [AVCOL_TRC_BT2020_12] = eotf_bt1886, + [AVCOL_TRC_SMPTE2084] = eotf_smpte_st2084, + [AVCOL_TRC_SMPTE428] = eotf_smpte_st428_1, + [AVCOL_TRC_ARIB_STD_B67] = eotf_arib_std_b67, +}; + +av_csp_eotf_function av_csp_itu_eotf(enum AVColorTransferCharacteristic trc) +{ + if (trc < 0 || trc >= AVCOL_TRC_NB) + return NULL; + return eotf_funcs[trc]; +} + +static const av_csp_eotf_function eotf_inv_funcs[AVCOL_TRC_NB] = { + [AVCOL_TRC_BT709] = eotf_bt1886_inv, + [AVCOL_TRC_GAMMA22] = eotf_gamma22_inv, + [AVCOL_TRC_GAMMA28] = eotf_gamma28_inv, + [AVCOL_TRC_SMPTE170M] = eotf_bt1886_inv, + [AVCOL_TRC_SMPTE240M] = eotf_bt1886_inv, + [AVCOL_TRC_LINEAR] = eotf_linear_inv, + [AVCOL_TRC_LOG] = NULL, + [AVCOL_TRC_LOG_SQRT] = NULL, + [AVCOL_TRC_IEC61966_2_4] = eotf_bt1886_inv, + [AVCOL_TRC_BT1361_ECG] = eotf_bt1886_inv, + [AVCOL_TRC_IEC61966_2_1] = eotf_iec61966_2_1_inv, + [AVCOL_TRC_BT2020_10] = eotf_bt1886_inv, + [AVCOL_TRC_BT2020_12] = eotf_bt1886_inv, + [AVCOL_TRC_SMPTE2084] = eotf_smpte_st2084_inv, + [AVCOL_TRC_SMPTE428] = eotf_smpte_st428_1_inv, + [AVCOL_TRC_ARIB_STD_B67] = eotf_arib_std_b67_inv, +}; + +av_csp_eotf_function av_csp_itu_eotf_inv(enum AVColorTransferCharacteristic trc) +{ + if (trc < 0 || trc >= AVCOL_TRC_NB) + return NULL; + return eotf_inv_funcs[trc]; +} diff --git a/libavutil/csp.h b/libavutil/csp.h index 58deebcb44..9b74c631d2 100644 --- a/libavutil/csp.h +++ b/libavutil/csp.h @@ -152,6 +152,39 @@ av_csp_trc_function av_csp_trc_func_from_id(enum AVColorTransferCharacteristic t */ av_csp_trc_function av_csp_trc_func_inv_from_id(enum AVColorTransferCharacteristic trc); +/** + * Function pointer representing an ITU EOTF transfer for a given reference + * display configuration. + * + * @param Lw The white point luminance of the display, in nits (cd/m^2). + * @param Lb The black point luminance of the display, in nits (cd/m^2). + */ +typedef void (*av_csp_eotf_function)(double Lw, double Lb, double c[3]); + +/** + * Returns the ITU EOTF corresponding to a given TRC. This converts from the + * signal level [0,1] to the raw output display luminance in nits (cd/m^2). + * This is done per channel in RGB space, except for AVCOL_TRC_SMPTE428, which + * assumes CIE XYZ in- and output. + * + * @return A pointer to the function implementing the given TRC, or NULL if no + * such function is defined. + * + * @note In general, the resulting function is defined (wherever possible) for + * out-of-range values, even though these values do not have a physical + * meaning on the given display. Users should clamp inputs (or outputs) + * if this behavior is not desired. + * + * This is also the case for functions like PQ, which are defined over an + * absolute signal range independent of the target display capabilities. + */ +av_csp_eotf_function av_csp_itu_eotf(enum AVColorTransferCharacteristic trc); + +/** + * Returns the mathematical inverse of the corresponding EOTF. + */ +av_csp_eotf_function av_csp_itu_eotf_inv(enum AVColorTransferCharacteristic trc); + /** * @} */ diff --git a/libavutil/version.h b/libavutil/version.h index efc569e090..ad1f3e68ba 100644 --- a/libavutil/version.h +++ b/libavutil/version.h @@ -79,7 +79,7 @@ */ #define LIBAVUTIL_VERSION_MAJOR 59 -#define LIBAVUTIL_VERSION_MINOR 48 +#define LIBAVUTIL_VERSION_MINOR 49 #define LIBAVUTIL_VERSION_MICRO 100 #define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \