[FFmpeg-devel] [PATCH v2 11/16] swscale/csputils: add internal colorspace math helpers
Niklas Haas
ffmpeg at haasn.xyz
Sat Dec 7 23:41:37 EET 2024
On Fri, 06 Dec 2024 10:16:23 -0500 Leo Izen <leo.izen at gmail.com> wrote:
>
>
> On 12/6/24 9:32 AM, Niklas Haas wrote:
> > From: Niklas Haas <git at haasn.dev>
> >
> > Logic is, for the most part, a straight port of similar logic in
> > liplacebo's colorspace.c, with some general edits and refactors.
> > ---
> > libswscale/Makefile | 1 +
> > libswscale/csputils.c | 412 ++++++++++++++++++++++++++++++++++++++++++
> > libswscale/csputils.h | 111 ++++++++++++
> > 3 files changed, 524 insertions(+)
> > create mode 100644 libswscale/csputils.c
> > create mode 100644 libswscale/csputils.h
> >
> > diff --git a/libswscale/Makefile b/libswscale/Makefile
> > index 81f32f4dd7..08036634b7 100644
> > --- a/libswscale/Makefile
> > +++ b/libswscale/Makefile
> > @@ -6,6 +6,7 @@ HEADERS = swscale.h \
> > version_major.h \
> >
> > OBJS = alphablend.o \
> > + csputils.o \
> > hscale.o \
> > hscale_fast_bilinear.o \
> > gamma.o \
> > diff --git a/libswscale/csputils.c b/libswscale/csputils.c
> > new file mode 100644
> > index 0000000000..479caff5dd
> > --- /dev/null
> > +++ b/libswscale/csputils.c
> > @@ -0,0 +1,412 @@
> > +/*
> > + * Copyright (C) 2024 Niklas Haas
> > + *
> > + * This file is part of FFmpeg.
> > + *
> > + * FFmpeg is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * FFmpeg is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with FFmpeg; if not, write to the Free Software
> > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> > + */
> > +
> > +#include "libavutil/csp.h"
> > +
> > +#include "csputils.h"
> > +#include "utils.h"
> > +
> > +void ff_sws_matrix3x3_mul(SwsMatrix3x3 *a, const SwsMatrix3x3 *b)
> > +{
> > + float a00 = a->m[0][0], a01 = a->m[0][1], a02 = a->m[0][2],
> > + a10 = a->m[1][0], a11 = a->m[1][1], a12 = a->m[1][2],
> > + a20 = a->m[2][0], a21 = a->m[2][1], a22 = a->m[2][2];
> > +
> > + for (int i = 0; i < 3; i++) {
> > + a->m[0][i] = a00 * b->m[0][i] + a01 * b->m[1][i] + a02 * b->m[2][i];
> > + a->m[1][i] = a10 * b->m[0][i] + a11 * b->m[1][i] + a12 * b->m[2][i];
> > + a->m[2][i] = a20 * b->m[0][i] + a21 * b->m[1][i] + a22 * b->m[2][i];
> > + }
> > +}
> > +
> > +void ff_sws_matrix3x3_rmul(const SwsMatrix3x3 *a, SwsMatrix3x3 *b)
> > +{
> > + float b00 = b->m[0][0], b01 = b->m[0][1], b02 = b->m[0][2],
> > + b10 = b->m[1][0], b11 = b->m[1][1], b12 = b->m[1][2],
> > + b20 = b->m[2][0], b21 = b->m[2][1], b22 = b->m[2][2];
> > +
> > + for (int i = 0; i < 3; i++) {
> > + b->m[i][0] = a->m[i][0] * b00 + a->m[i][1] * b10 + a->m[i][2] * b20;
> > + b->m[i][1] = a->m[i][0] * b01 + a->m[i][1] * b11 + a->m[i][2] * b21;
> > + b->m[i][2] = a->m[i][0] * b02 + a->m[i][1] * b12 + a->m[i][2] * b22;
> > + }
> > +}
> > +
> > +void ff_sws_matrix3x3_invert(SwsMatrix3x3 *mat)
> > +{
> > + double m00 = mat->m[0][0], m01 = mat->m[0][1], m02 = mat->m[0][2],
> > + m10 = mat->m[1][0], m11 = mat->m[1][1], m12 = mat->m[1][2],
> > + m20 = mat->m[2][0], m21 = mat->m[2][1], m22 = mat->m[2][2];
> > +
> > + // calculate the adjoint
> > + double a00 = (m11 * m22 - m21 * m12);
> > + double a01 = -(m01 * m22 - m21 * m02);
> > + double a02 = (m01 * m12 - m11 * m02);
> > + double a10 = -(m10 * m22 - m20 * m12);
> > + double a11 = (m00 * m22 - m20 * m02);
> > + double a12 = -(m00 * m12 - m10 * m02);
> > + double a20 = (m10 * m21 - m20 * m11);
> > + double a21 = -(m00 * m21 - m20 * m01);
> > + double a22 = (m00 * m11 - m10 * m01);
> > +
> > + // calculate the determinant (as inverse == 1/det * adjoint,
> > + // adjoint * m == identity * det, so this calculates the det)
> > + double det = m00 * a00 + m10 * a01 + m20 * a02;
> > + det = 1.0 / det;
> > +
> > + mat->m[0][0] = det * a00;
> > + mat->m[0][1] = det * a01;
> > + mat->m[0][2] = det * a02;
> > + mat->m[1][0] = det * a10;
> > + mat->m[1][1] = det * a11;
> > + mat->m[1][2] = det * a12;
> > + mat->m[2][0] = det * a20;
> > + mat->m[2][1] = det * a21;
> > + mat->m[2][2] = det * a22;
> > +}
> > +
> > +void ff_sws_matrix3x3_apply(const SwsMatrix3x3 *mat, float vec[3])
> > +{
> > + float x = vec[0], y = vec[1], z = vec[2];
> > +
> > + for (int i = 0; i < 3; i++)
> > + vec[i] = mat->m[i][0] * x + mat->m[i][1] * y + mat->m[i][2] * z;
> > +}
> > +
> > +/* Recovers (X / Y) from a CIE xy value. */
> > +static inline AVRational cie_X(AVCIExy xy)
> > +{
> > + return av_div_q(xy.x, xy.y);
> > +}
> > +
> > +/* Recovers (Z / Y) from a CIE xy value. */
> > +static inline AVRational cie_Z(AVCIExy xy)
> > +{
> > + return av_div_q(av_sub_q(av_sub_q(av_make_q(1, 1), xy.x), xy.y), xy.y);
> > +}
> > +
> > +SwsMatrix3x3 ff_sws_rgb2xyz(const AVColorPrimariesDesc *desc)
>
> Does XYZ here use the same whitepoint as the RGB or does it use D50? May
> make sense to add a comment elaborating.
It uses the same whitepoint as the RGB. It is just a direct conversion to
XYZ. I'll add a comment to clarify that.
>
> > +{
> > + SwsMatrix3x3 out = {{{0}}};
> > + float S[3], X[4], Z[4];
> > +
> > + X[0] = av_q2d(cie_X(desc->prim.r));
> > + X[1] = av_q2d(cie_X(desc->prim.g));
> > + X[2] = av_q2d(cie_X(desc->prim.b));
> > + X[3] = av_q2d(cie_X(desc->wp));
> > +
> > + Z[0] = av_q2d(cie_Z(desc->prim.r));
> > + Z[1] = av_q2d(cie_Z(desc->prim.g));
> > + Z[2] = av_q2d(cie_Z(desc->prim.b));
> > + Z[3] = av_q2d(cie_Z(desc->wp));
> > +
> > + // S = XYZ^-1 * W
> > + for (int i = 0; i < 3; i++) {
> > + out.m[0][i] = X[i];
> > + out.m[1][i] = 1;
> > + out.m[2][i] = Z[i];
> > + }
> > +
> > + ff_sws_matrix3x3_invert(&out);
> > +
> > + for (int i = 0; i < 3; i++)
> > + S[i] = out.m[i][0] * X[3] + out.m[i][1] * 1 + out.m[i][2] * Z[3];
>
> Is this hardcoded 3 intentional? i.e. whitepoint?
Yes. I've rewritten the code to use an explicit name, since there's no reason
to have it live inside the same array.
> > +
> > + // M = [Sc * XYZc]
> > + for (int i = 0; i < 3; i++) {
> > + out.m[0][i] = S[i] * X[i];
> > + out.m[1][i] = S[i] * 1;
> > + out.m[2][i] = S[i] * Z[i];
> > + }
> > +
> > + return out;
> > +}
> > +
> > +SwsMatrix3x3 ff_sws_xyz2rgb(const AVColorPrimariesDesc *prim)
> > +{
> > + SwsMatrix3x3 out = ff_sws_rgb2xyz(prim);
> > + ff_sws_matrix3x3_invert(&out);
> > + return out;
> > +}
> > +
> > +/* Matrix used in CAT16, a revised one-step linear transform method */
> > +static const SwsMatrix3x3 m_cat16 = {{
> > + { 0.401288f, 0.650173f, -0.051461f },
> > + { -0.250268f, 1.204414f, 0.045854f },
> > + { -0.002079f, 0.048952f, 0.953127f },
> > +}};
> > +
> > +static const SwsMatrix3x3 m_cat16_inv = {{
> > + { 1.862068f, -1.011255f, 0.149187f },
> > + { 0.387527f, 0.621447f, -0.008974f },
> > + { -0.015841f, -0.034123f, 1.049964f },
> > +}};
> > +
> > +// M := M * XYZd<-XYZs
> > +static void apply_chromatic_adaptation(AVCIExy src, AVCIExy dst,
> > + SwsMatrix3x3 *mat)
> > +{
> > + SwsMatrix3x3 tmp = {0};
> > + float C[3][2];
> > + const float srcX = av_q2d(cie_X(src)),
> > + srcZ = av_q2d(cie_Z(src)),
> > + dstX = av_q2d(cie_X(dst)),
> > + dstZ = av_q2d(cie_Z(dst));
> > +
> > + if (ff_cie_xy_equal(src, dst))
> > + return;
> > +
> > + // Linear "von Kries" method, adapted from CIECAM16
> > + // http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html
>
> Why von Kries on not Bradford? The cited link says Brandford is "better."
The page is referring to the matrix originally used by von Kries back in the
early 20th century. The matrix we use is from CIECAT16, a very modern standard
which is numerically optimized across a large database of perceptual color
pairs and is IIRC also suitable for use in high dynamic range applications.
It scores comparably or better than Bradford in almost all cases.
> > +
> > + for (int i = 0; i < 3; i++) {
> > + // source cone
> > + C[i][0] = m_cat16.m[i][0] * srcX
> > + + m_cat16.m[i][1] * 1
> > + + m_cat16.m[i][2] * srcZ,
> > +
> > + // dest cone
> > + C[i][1] = m_cat16.m[i][0] * dstX
> > + + m_cat16.m[i][1] * 1
> > + + m_cat16.m[i][2] * dstZ;
> > + }
> > +
> > + // tmp := I * [Cd/Cs] * Ma
> > + for (int i = 0; i < 3; i++)
> > + tmp.m[i][i] = C[i][1] / C[i][0];
> > +
> > + ff_sws_matrix3x3_mul(&tmp, &m_cat16);
> > +
> > + // M := M * Ma^-1 * tmp
> > + ff_sws_matrix3x3_mul(mat, &m_cat16_inv);
> > + ff_sws_matrix3x3_mul(mat, &tmp);
> > +}
> > +
> > +SwsMatrix3x3 ff_sws_get_adaptation(const AVPrimaryCoefficients *prim,
> > + AVCIExy from, AVCIExy to)
> > +{
>
> If the intent is that "from" and "to" are white points, use
> AVWhitepointCoefficients instead. It's typedef'd from AVCIExy
> but it makes intent a bit clearer.
Fixed; also for the numerous internal helpers.
>
> > + SwsMatrix3x3 rgb2xyz, xyz2rgb;
> > + const AVColorPrimariesDesc csp = {
> > + .prim = *prim,
> > + .wp = from,
> > + };
> > +
> > + rgb2xyz = ff_sws_rgb2xyz(&csp);
> > + xyz2rgb = ff_sws_xyz2rgb(&csp);
> > + apply_chromatic_adaptation(from, to, &xyz2rgb);
> > + ff_sws_matrix3x3_mul(&xyz2rgb, &rgb2xyz);
> > + return xyz2rgb;
> > +}
> > +
> > +static const AVCIExy d65 = { .x = {3127, 10000}, .y = {3290, 10000} };
>
> static const AVWhitepointCoefficients d65
Changed.
>
> > +
> > +SwsMatrix3x3 ff_sws_ipt_rgb2lms(const AVColorPrimariesDesc *prim)
> > +{
> > + static const SwsMatrix3x3 hpe = {{ /* HPE XYZ->LMS (D65) method */
> > + { 0.40024f, 0.70760f, -0.08081f },
> > + { -0.22630f, 1.16532f, 0.04570f },
> > + { 0.00000f, 0.00000f, 0.91822f },
> > + }};
>
> Should hpe be delcared in the function or above it? May be cleaner
> to declare the static const foo outside of the function.
Changed.
>
> > +
> > + const float c = 0.04f; // 4% crosstalk
> > + SwsMatrix3x3 rgb2xyz;
> > + SwsMatrix3x3 m = {{
> > + { 1 - 2*c, c, c },
> > + { c, 1 - 2*c, c },
> > + { c, c, 1 - 2*c },
> > + }};
> > +
> > + ff_sws_matrix3x3_mul(&m, &hpe);
> > +
> > + // Apply chromatic adaptation to D65 if the input white point differs
> > + apply_chromatic_adaptation(prim->wp, d65, &m);
> > +
> > + rgb2xyz = ff_sws_rgb2xyz(prim);
> > + ff_sws_matrix3x3_mul(&m, &rgb2xyz);
> > + return m;
> > +}
> > +
> > +SwsMatrix3x3 ff_sws_ipt_lms2rgb(const AVColorPrimariesDesc *prim)
> > +{
> > + SwsMatrix3x3 rgb2lms = ff_sws_ipt_rgb2lms(prim);
> > + ff_sws_matrix3x3_invert(&rgb2lms);
> > + return rgb2lms;
> > +}
> > +
> > +/* Test the sign of 'p' relative to the line 'ab' (barycentric coordinates) */
> > +static int test_point_line(AVCIExy p, AVCIExy a, AVCIExy b)
> > +{
> > + return av_cmp_q(av_mul_q(av_sub_q(p.x, b.x), av_sub_q(a.y, b.y)),
> > + av_mul_q(av_sub_q(a.x, b.x), av_sub_q(p.y, b.y)));
> > +}
> > +
> > +
> > +/* Test if a point is entirely inside a gamut */
> > +static float test_point_gamut(const AVCIExy point,
> > + const AVPrimaryCoefficients *prim)
> > +{
> > + int d1 = test_point_line(point, prim->r, prim->g),
> > + d2 = test_point_line(point, prim->g, prim->b),
> > + d3 = test_point_line(point, prim->b, prim->r);
> > +
> > + bool has_neg = d1 < 0 || d2 < 0 || d3 < 0,
> > + has_pos = d1 > 0 || d2 > 0 || d3 > 0;
>
> I don't think we use bool in FFmpeg. It's always int.
I asked on #ffmpeg-devel and was given the okay to start using bool in internal
code / headers. I really don't see the big deal, `bool` clearly communicates
intent and should not be slower in any reasonable scenario.
> > +
> > + return !(has_neg && has_pos);
> > +}
> > +
> > +bool ff_prim_superset(const AVPrimaryCoefficients *a, const AVPrimaryCoefficients *b)
> > +{
> > + return test_point_gamut(b->r, a) &&
> > + test_point_gamut(b->g, a) &&
> > + test_point_gamut(b->b, a);
> > +}
> > +
> > +const float pq_eotf_lut[PQ_LUT_SIZE+1] = {
> > + 0.0000000e+00f, 4.0422718e-05f, 1.3111372e-04f, 2.6236826e-04f, 4.3151495e-04f, 6.3746885e-04f, 8.7982383e-04f, 1.1585362e-03f,
> > + 1.4737819e-03f, 1.8258818e-03f, 2.2152586e-03f, 2.6424098e-03f, 3.1078907e-03f, 3.6123021e-03f, 4.1562821e-03f, 4.7405001e-03f,
> > + 5.3656521e-03f, 6.0324583e-03f, 6.7416568e-03f, 7.4940095e-03f, 8.2902897e-03f, 9.1312924e-03f, 1.0017822e-02f, 1.0950702e-02f,
> > + 1.1930764e-02f, 1.2958861e-02f, 1.4035847e-02f, 1.5162600e-02f, 1.6340000e-02f, 1.7568948e-02f, 1.8850346e-02f, 2.0185119e-02f,
> > + 2.1574192e-02f, 2.3018509e-02f, 2.4519029e-02f, 2.6076704e-02f, 2.7692516e-02f, 2.9367449e-02f, 3.1102509e-02f, 3.2898690e-02f,
> > + 3.4757019e-02f, 3.6678526e-02f, 3.8664261e-02f, 4.0715262e-02f, 4.2832601e-02f, 4.5017354e-02f, 4.7270617e-02f, 4.9593473e-02f,
> > + 5.1987040e-02f, 5.4452441e-02f, 5.6990819e-02f, 5.9603301e-02f, 6.2291055e-02f, 6.5055251e-02f, 6.7897080e-02f, 7.0817717e-02f,
> > + 7.3818379e-02f, 7.6900283e-02f, 8.0064675e-02f, 8.3312774e-02f, 8.6645849e-02f, 9.0065169e-02f, 9.3572031e-02f, 9.7167704e-02f,
> > + 1.0085351e-01f, 1.0463077e-01f, 1.0850082e-01f, 1.1246501e-01f, 1.1652473e-01f, 1.2068130e-01f, 1.2493614e-01f, 1.2929066e-01f,
> > + 1.3374626e-01f, 1.3830439e-01f, 1.4296648e-01f, 1.4773401e-01f, 1.5260848e-01f, 1.5759132e-01f, 1.6268405e-01f, 1.6788821e-01f,
> > + 1.7320534e-01f, 1.7863697e-01f, 1.8418467e-01f, 1.8985004e-01f, 1.9563470e-01f, 2.0154019e-01f, 2.0756818e-01f, 2.1372031e-01f,
> > + 2.1999824e-01f, 2.2640365e-01f, 2.3293824e-01f, 2.3960372e-01f, 2.4640186e-01f, 2.5333431e-01f, 2.6040288e-01f, 2.6760935e-01f,
> > + 2.7495552e-01f, 2.8244319e-01f, 2.9007421e-01f, 2.9785041e-01f, 3.0577373e-01f, 3.1384594e-01f, 3.2206899e-01f, 3.3044481e-01f,
> > + 3.3897533e-01f, 3.4766253e-01f, 3.5650838e-01f, 3.6551487e-01f, 3.7468409e-01f, 3.8401794e-01f, 3.9351855e-01f, 4.0318799e-01f,
> > + 4.1302836e-01f, 4.2304177e-01f, 4.3323036e-01f, 4.4359629e-01f, 4.5414181e-01f, 4.6486897e-01f, 4.7578006e-01f, 4.8687732e-01f,
> > + 4.9816302e-01f, 5.0963944e-01f, 5.2130889e-01f, 5.3317369e-01f, 5.4523628e-01f, 5.5749886e-01f, 5.6996391e-01f, 5.8263384e-01f,
> > + 5.9551111e-01f, 6.0859816e-01f, 6.2189750e-01f, 6.3541162e-01f, 6.4914307e-01f, 6.6309439e-01f, 6.7726819e-01f, 6.9166705e-01f,
> > + 7.0629384e-01f, 7.2115077e-01f, 7.3624074e-01f, 7.5156646e-01f, 7.6713065e-01f, 7.8293608e-01f, 7.9898553e-01f, 8.1528181e-01f,
> > + 8.3182776e-01f, 8.4862623e-01f, 8.6568012e-01f, 8.8299235e-01f, 9.0056585e-01f, 9.1840360e-01f, 9.3650860e-01f, 9.5488388e-01f,
> > + 9.7353277e-01f, 9.9245779e-01f, 1.0116623e+00f, 1.0311496e+00f, 1.0509226e+00f, 1.0709847e+00f, 1.0913391e+00f, 1.1119889e+00f,
> > + 1.1329376e+00f, 1.1541885e+00f, 1.1757448e+00f, 1.1976100e+00f, 1.2197875e+00f, 1.2422807e+00f, 1.2650931e+00f, 1.2882282e+00f,
> > + 1.3116900e+00f, 1.3354812e+00f, 1.3596059e+00f, 1.3840676e+00f, 1.4088701e+00f, 1.4340170e+00f, 1.4595121e+00f, 1.4853593e+00f,
> > + 1.5115622e+00f, 1.5381247e+00f, 1.5650507e+00f, 1.5923442e+00f, 1.6200090e+00f, 1.6480492e+00f, 1.6764688e+00f, 1.7052718e+00f,
> > + 1.7344629e+00f, 1.7640451e+00f, 1.7940233e+00f, 1.8244015e+00f, 1.8551840e+00f, 1.8863752e+00f, 1.9179792e+00f, 1.9500006e+00f,
> > + 1.9824437e+00f, 2.0153130e+00f, 2.0486129e+00f, 2.0823479e+00f, 2.1165227e+00f, 2.1511419e+00f, 2.1862101e+00f, 2.2217319e+00f,
> > + 2.2577128e+00f, 2.2941563e+00f, 2.3310679e+00f, 2.3684523e+00f, 2.4063146e+00f, 2.4446597e+00f, 2.4834925e+00f, 2.5228182e+00f,
> > + 2.5626417e+00f, 2.6029683e+00f, 2.6438031e+00f, 2.6851514e+00f, 2.7270184e+00f, 2.7694094e+00f, 2.8123299e+00f, 2.8557852e+00f,
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> > + 5.1927219e+03f, 5.2403759e+03f, 5.2884795e+03f, 5.3370373e+03f, 5.3860537e+03f, 5.4355333e+03f, 5.4854807e+03f, 5.5359004e+03f,
> > + 5.5867972e+03f, 5.6381757e+03f, 5.6900408e+03f, 5.7423972e+03f, 5.7952499e+03f, 5.8486037e+03f, 5.9024637e+03f, 5.9568349e+03f,
> > + 6.0117223e+03f, 6.0671311e+03f, 6.1230664e+03f, 6.1795336e+03f, 6.2365379e+03f, 6.2940847e+03f, 6.3521793e+03f, 6.4108273e+03f,
> > + 6.4700342e+03f, 6.5298056e+03f, 6.5901471e+03f, 6.6510643e+03f, 6.7125632e+03f, 6.7746495e+03f, 6.8373290e+03f, 6.9006078e+03f,
> > + 6.9644918e+03f, 7.0289872e+03f, 7.0941001e+03f, 7.1598366e+03f, 7.2262031e+03f, 7.2932059e+03f, 7.3608513e+03f, 7.4291460e+03f,
> > + 7.4981006e+03f, 7.5677134e+03f, 7.6379952e+03f, 7.7089527e+03f, 7.7805929e+03f, 7.8529226e+03f, 7.9259489e+03f, 7.9996786e+03f,
> > + 8.0741191e+03f, 8.1492774e+03f, 8.2251609e+03f, 8.3017769e+03f, 8.3791329e+03f, 8.4572364e+03f, 8.5360950e+03f, 8.6157163e+03f,
> > + 8.6961082e+03f, 8.7772786e+03f, 8.8592352e+03f, 8.9419862e+03f, 9.0255397e+03f, 9.1099038e+03f, 9.1950869e+03f, 9.2810973e+03f,
> > + 9.3679435e+03f, 9.4556340e+03f, 9.5441776e+03f, 9.6335829e+03f, 9.7238588e+03f, 9.8150143e+03f, 9.9070583e+03f, 1.0000000e+04f,
> > + 1e4f, /* extra padding to avoid out of bounds access */
> > +};
>
> If this isn't static const and the intent is to reference it internally
> and not externally it needs to have an ff_ prefix.
Fixed.
>
>
> > diff --git a/libswscale/csputils.h b/libswscale/csputils.h
> > new file mode 100644
> > index 0000000000..6c81fcdd65
> > --- /dev/null
> > +++ b/libswscale/csputils.h
> > @@ -0,0 +1,111 @@
> > +/*
> > + * Copyright (C) 2024 Niklas Haas
> > + *
> > + * This file is part of FFmpeg.
> > + *
> > + * FFmpeg is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * FFmpeg is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with FFmpeg; if not, write to the Free Software
> > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> > + */
> > +
> > +#ifndef SWSCALE_CSPUTILS_H
> > +#define SWSCALE_CSPUTILS_H
> > +
> > +#include <stdint.h>
> > +#include <stdbool.h>
> > +#include <math.h>
> > +
> > +#include "libavutil/attributes.h"
> > +#include "libavutil/common.h"
> > +#include "libavutil/csp.h"
> > +#include "libavutil/pixfmt.h"
> > +
> > +/* Shared constants and helpers for colorspace mapping */
> > +
> > +#define fmixf(a, b, x) ((b) * (x) + (a) * (1 - (x)))
> > +
> > +static inline float smoothstepf(float edge0, float edge1, float x)
> > +{
> > + if (edge0 == edge1)
> > + return x >= edge0;
>
> Floating point ==
> Tolerance instead perhaps? If edge1 and edge0 are very close then in the
> next step dividing by a very small number will make x blow up.
That is fine. Even if the divisor escapes to infinity, the result is well
behaved and consistant with the mathematical definition. Note the clamp
immediately following the division.
In theory, we could skip this check and rely on (x - edge0) / 0 == +/- inf
to clamp down to the correct value of 0 or 1 respectively, but this breaks
for the edge case of 0 / 0 (i.e. smoothstep(x, x, x) = undefined). The branch
here provides a default value for this edge case, in this case biasing the
function high, i.e. smoothstep(x, x, x) = 1.
In either case, this is a well known floating point operation provided by
e.g. GPUs, and I don't see any reason to deviate from established behavior.
>
> > + x = (x - edge0) / (edge1 - edge0);
> > + x = av_clipf(x, 0.0f, 1.0f);
> > + return x * x * (3.0f - 2.0f * x);
> > +}
> > +
> > +/* 3x3 matrix math */
> > +typedef struct SwsMatrix3x3 {
> > + float m[3][3];
> > +} SwsMatrix3x3;
> > +
> > +void ff_sws_matrix3x3_mul(SwsMatrix3x3 *a, const SwsMatrix3x3 *b);
> > +void ff_sws_matrix3x3_rmul(const SwsMatrix3x3 *a, SwsMatrix3x3 *b);
> > +void ff_sws_matrix3x3_invert(SwsMatrix3x3 *mat);
> > +void ff_sws_matrix3x3_apply(const SwsMatrix3x3 *mat, float vec[3]);
> > +
> > +SwsMatrix3x3 ff_sws_ipt_rgb2lms(const AVColorPrimariesDesc *prim);
> > +SwsMatrix3x3 ff_sws_ipt_lms2rgb(const AVColorPrimariesDesc *prim);
> > +SwsMatrix3x3 ff_sws_rgb2xyz(const AVColorPrimariesDesc *prim);
> > +SwsMatrix3x3 ff_sws_xyz2rgb(const AVColorPrimariesDesc *prim);
> > +
> > +/* Returns an RGB -> RGB adaptation matrix */
> > +SwsMatrix3x3 ff_sws_get_adaptation(const AVPrimaryCoefficients *prim,
> > + AVCIExy from, AVCIExy to);
> > +
> > +/* Integer math definitions / helpers */
> > +typedef struct v3u8_t {
> > + uint8_t x, y, z;
> > +} v3u8_t;
> > +
> > +typedef struct v2u16_t {
> > + uint16_t x, y;
> > +} v2u16_t;
> > +
> > +typedef struct v3u16_t {
> > + uint16_t x, y, z;
> > +} v3u16_t;
> > +
>
> Do these helpers belong in a header file? If the goal is simply to
> include them in other sws things, then should we prefix them as with
> FFv3u16_t? I'm not sure the policy here.
No comment.
>
> > +/* Fast perceptual quantizer */
> > +static const float PQ_M1 = 2610./4096 * 1./4,
> > + PQ_M2 = 2523./4096 * 128,
> > + PQ_C1 = 3424./4096,
> > + PQ_C2 = 2413./4096 * 32,
> > + PQ_C3 = 2392./4096 * 32;
> > +
> > +enum { PQ_LUT_SIZE = 1024 };
> > +extern const float pq_eotf_lut[PQ_LUT_SIZE+1];
> > +
> > +static inline float pq_eotf(float x)
> > +{
> > + float idxf = av_clipf(x, 0.0f, 1.0f) * (PQ_LUT_SIZE - 1);
> > + int ipart = floorf(idxf);
> > + float fpart = idxf - ipart;
> > + return fmixf(pq_eotf_lut[ipart], pq_eotf_lut[ipart + 1], fpart);
> > +}
> > +
> > +static inline float pq_oetf(float x)
> > +{
> > + x = powf(fmaxf(x * 1e-4f, 0.0f), PQ_M1);
> > + x = (PQ_C1 + PQ_C2 * x) / (1.0f + PQ_C3 * x);
> > + return powf(x, PQ_M2);
> > +}
> > +
> > +/* Misc colorspace math / helpers */
> > +
> > +/**
> > + * Returns true if 'b' is entirely contained in 'a'. Useful for figuring out if
> > + * colorimetric clipping will occur or not.
> > + */
> > +bool ff_prim_superset(const AVPrimaryCoefficients *a, const AVPrimaryCoefficients *b);
> > +
> > +#endif /* SWSCALE_CSPUTILS_H */
>
> - Leo Izen (Traneptora)
Thanks for the review.
>
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