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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).
This commit is contained in:
Niklas Haas
parent
bf0a6c4111
commit
06f084468e
@ -2,6 +2,9 @@ The last version increases of all libraries were on 2024-03-07
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API changes, most recent first:
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2024-12-05 - xxxxxxxxxx - lavu 59.49.100 - csp.h
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Add av_csp_itu_eotf() and av_csp_itu_eotf_inv().
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2024-12-05 - xxxxxxxxxx - lavu 59.48.100 - csp.h
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Add av_csp_trc_func_inv_from_id().
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205
libavutil/csp.c
205
libavutil/csp.c
@ -429,3 +429,208 @@ av_csp_trc_function av_csp_trc_func_inv_from_id(enum AVColorTransferCharacterist
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return NULL;
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return trc_inv_funcs[trc];
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}
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static void eotf_linear(const double Lw, const double Lb, double E[3])
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{
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for (int i = 0; i < 3; i++)
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E[i] = (Lw - Lb) * E[i] + Lb;
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}
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static void eotf_linear_inv(const double Lw, const double Lb, double L[3])
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{
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for (int i = 0; i < 3; i++)
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L[i] = (L[i] - Lb) / (Lw - Lb);
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}
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#define WRAP_SDR_OETF(name) \
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static void oetf_##name(double L[3]) \
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{ \
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for (int i = 0; i < 3; i++) \
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L[i] = trc_##name(L[i]); \
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} \
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\
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static void oetf_##name##_inv(double E[3]) \
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{ \
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for (int i = 0; i < 3; i++) \
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E[i] = trc_##name##_inv(E[i]); \
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}
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WRAP_SDR_OETF(gamma22)
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WRAP_SDR_OETF(gamma28)
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WRAP_SDR_OETF(iec61966_2_1)
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#define WRAP_SDR_EOTF(name) \
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static void eotf_##name(double Lw, double Lb, double E[3]) \
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{ \
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oetf_##name##_inv(E); \
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eotf_linear(Lw, Lb, E); \
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} \
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\
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static void eotf_##name##_inv(double Lw, double Lb, double L[3]) \
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{ \
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eotf_linear_inv(Lw, Lb, L); \
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oetf_##name(L); \
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}
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WRAP_SDR_EOTF(gamma22)
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WRAP_SDR_EOTF(gamma28)
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WRAP_SDR_EOTF(iec61966_2_1)
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static void eotf_bt1886(const double Lw, const double Lb, double E[3])
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{
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const double Lw_inv = pow(Lw, 1.0 / 2.4);
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const double Lb_inv = pow(Lb, 1.0 / 2.4);
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const double a = pow(Lw_inv - Lb_inv, 2.4);
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const double b = Lb_inv / (Lw_inv - Lb_inv);
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for (int i = 0; i < 3; i++)
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E[i] = (-b > E[i]) ? 0.0 : a * pow(E[i] + b, 2.4);
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}
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static void eotf_bt1886_inv(const double Lw, const double Lb, double L[3])
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{
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const double Lw_inv = pow(Lw, 1.0 / 2.4);
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const double Lb_inv = pow(Lb, 1.0 / 2.4);
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const double a = pow(Lw_inv - Lb_inv, 2.4);
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const double b = Lb_inv / (Lw_inv - Lb_inv);
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for (int i = 0; i < 3; i++)
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L[i] = (0.0 > L[i]) ? 0.0 : pow(L[i] / a, 1.0 / 2.4) - b;
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}
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static void eotf_smpte_st2084(const double Lw, const double Lb, double E[3])
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{
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for (int i = 0; i < 3; i++)
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E[i] = trc_smpte_st2084_inv(E[i]);
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}
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static void eotf_smpte_st2084_inv(const double Lw, const double Lb, double L[3])
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{
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for (int i = 0; i < 3; i++)
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L[i] = trc_smpte_st2084(L[i]);
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}
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/* This implementation assumes an SMPTE RP 431-2 reference projector (DCI) */
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#define DCI_L 48.00
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#define DCI_P 52.37
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#define DCI_X (42.94 / DCI_L)
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#define DCI_Z (45.82 / DCI_L)
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static void eotf_smpte_st428_1(const double Lw_Y, const double Lb_Y, double E[3])
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{
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const double Lw[3] = { DCI_X * Lw_Y, Lw_Y, DCI_Z * Lw_Y };
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const double Lb[3] = { DCI_X * Lb_Y, Lb_Y, DCI_Z * Lb_Y };
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for (int i = 0; i < 3; i++) {
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E[i] = (0.0 > E[i]) ? 0.0 : pow(E[i], 2.6) * DCI_P / DCI_L;
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E[i] = E[i] * (Lw[i] - Lb[i]) + Lb[i];
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}
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}
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static void eotf_smpte_st428_1_inv(const double Lw_Y, const double Lb_Y, double L[3])
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{
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const double Lw[3] = { DCI_X * Lw_Y, Lw_Y, DCI_Z * Lw_Y };
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const double Lb[3] = { DCI_X * Lb_Y, Lb_Y, DCI_Z * Lb_Y };
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for (int i = 0; i < 3; i++) {
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L[i] = (L[i] - Lb[i]) / (Lw[i] - Lb[i]);
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L[i] = (0.0 > L[i]) ? 0.0 : pow(L[i] * DCI_L / DCI_P, 1.0 / 2.6);
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}
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}
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static void eotf_arib_std_b67(const double Lw, const double Lb, double E[3])
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{
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const double gamma = fmax(1.2 + 0.42 * log10(Lw / 1000.0), 1.0);
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/**
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* Note: This equation is technically only accurate if the contrast ratio
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* Lw:Lb is greater than 12:1; otherwise we would need to use a different,
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* significantly more complicated solution. Ignore this as a highly
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* degenerate case, since any real world reference display will have a
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* static contrast ratio multiple orders of magnitude higher.
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*/
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const double beta = sqrt(3 * pow(Lb / Lw, 1.0 / gamma));
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double luma;
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for (int i = 0; i < 3; i++)
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E[i] = trc_arib_std_b67_inv((1 - beta) * E[i] + beta);
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luma = 0.2627 * E[0] + 0.6780 * E[1] + 0.0593 * E[2];
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luma = pow(fmax(luma, 0.0), gamma - 1.0);
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for (int i = 0; i < 3; i++)
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E[i] *= Lw * luma;
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}
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static void eotf_arib_std_b67_inv(const double Lw, const double Lb, double L[3])
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{
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const double gamma = fmax(1.2 + 0.42 * log10(Lw / 1000.0), 1.0);
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const double beta = sqrt(3 * pow(Lb / Lw, 1 / gamma));
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double luma = 0.2627 * L[0] + 0.6780 * L[1] + 0.0593 * L[2];
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if (luma > 0.0) {
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luma = pow(luma / Lw, (1 - gamma) / gamma);
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for (int i = 0; i < 3; i++)
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L[i] *= luma / Lw;
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} else {
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L[0] = L[1] = L[2] = 0.0;
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}
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for (int i = 0; i < 3; i++)
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L[i] = (trc_arib_std_b67(L[i]) - beta) / (1 - beta);
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}
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static const av_csp_eotf_function eotf_funcs[AVCOL_TRC_NB] = {
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[AVCOL_TRC_BT709] = eotf_bt1886,
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[AVCOL_TRC_GAMMA22] = eotf_gamma22,
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[AVCOL_TRC_GAMMA28] = eotf_gamma28,
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[AVCOL_TRC_SMPTE170M] = eotf_bt1886,
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[AVCOL_TRC_SMPTE240M] = eotf_bt1886,
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[AVCOL_TRC_LINEAR] = eotf_linear,
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/* There is no EOTF associated with these logarithmic encodings, since they
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* are defined purely for transmission of scene referred data. */
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[AVCOL_TRC_LOG] = NULL,
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[AVCOL_TRC_LOG_SQRT] = NULL,
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/* BT.1886 is already defined for values below 0.0, as far as physically
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* meaningful, so we can directly use it for extended range encodings */
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[AVCOL_TRC_IEC61966_2_4] = eotf_bt1886,
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[AVCOL_TRC_BT1361_ECG] = eotf_bt1886,
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[AVCOL_TRC_IEC61966_2_1] = eotf_iec61966_2_1,
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[AVCOL_TRC_BT2020_10] = eotf_bt1886,
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[AVCOL_TRC_BT2020_12] = eotf_bt1886,
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[AVCOL_TRC_SMPTE2084] = eotf_smpte_st2084,
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[AVCOL_TRC_SMPTE428] = eotf_smpte_st428_1,
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[AVCOL_TRC_ARIB_STD_B67] = eotf_arib_std_b67,
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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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if (trc < 0 || trc >= AVCOL_TRC_NB)
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return NULL;
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return eotf_funcs[trc];
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}
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static const av_csp_eotf_function eotf_inv_funcs[AVCOL_TRC_NB] = {
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[AVCOL_TRC_BT709] = eotf_bt1886_inv,
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[AVCOL_TRC_GAMMA22] = eotf_gamma22_inv,
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[AVCOL_TRC_GAMMA28] = eotf_gamma28_inv,
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[AVCOL_TRC_SMPTE170M] = eotf_bt1886_inv,
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[AVCOL_TRC_SMPTE240M] = eotf_bt1886_inv,
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[AVCOL_TRC_LINEAR] = eotf_linear_inv,
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[AVCOL_TRC_LOG] = NULL,
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[AVCOL_TRC_LOG_SQRT] = NULL,
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[AVCOL_TRC_IEC61966_2_4] = eotf_bt1886_inv,
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[AVCOL_TRC_BT1361_ECG] = eotf_bt1886_inv,
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[AVCOL_TRC_IEC61966_2_1] = eotf_iec61966_2_1_inv,
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[AVCOL_TRC_BT2020_10] = eotf_bt1886_inv,
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[AVCOL_TRC_BT2020_12] = eotf_bt1886_inv,
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[AVCOL_TRC_SMPTE2084] = eotf_smpte_st2084_inv,
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[AVCOL_TRC_SMPTE428] = eotf_smpte_st428_1_inv,
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[AVCOL_TRC_ARIB_STD_B67] = eotf_arib_std_b67_inv,
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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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if (trc < 0 || trc >= AVCOL_TRC_NB)
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return NULL;
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return eotf_inv_funcs[trc];
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}
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@ -152,6 +152,39 @@ av_csp_trc_function av_csp_trc_func_from_id(enum AVColorTransferCharacteristic t
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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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@ -79,7 +79,7 @@
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*/
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#define LIBAVUTIL_VERSION_MAJOR 59
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#define LIBAVUTIL_VERSION_MINOR 48
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#define LIBAVUTIL_VERSION_MINOR 49
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#define LIBAVUTIL_VERSION_MICRO 100
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#define LIBAVUTIL_VERSION_INT AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
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