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+// Copyright (c) the JPEG XL Project Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Re-implementation of //tools/ssimulacra.tct using jxl's
+// ImageF library instead of opencv.
+
+#include "tools/ssimulacra.h"
+
+#include <cmath>
+
+#include "lib/jxl/gauss_blur.h"
+#include "lib/jxl/image_ops.h"
+
+namespace ssimulacra {
+namespace {
+
+using jxl::Image3F;
+using jxl::ImageF;
+
+static const float kC1 = 0.0001f;
+static const float kC2 = 0.0004f;
+static const int kNumScales = 6;
+// Premultiplied by chroma weight 0.2
+static const double kScaleWeights[kNumScales][3] = {
+ {0.04480, 0.00300, 0.00300}, {0.28560, 0.00896, 0.00896},
+ {0.30010, 0.05712, 0.05712}, {0.23630, 0.06002, 0.06002},
+ {0.13330, 0.06726, 0.06726}, {0.10000, 0.05000, 0.05000},
+};
+// Premultiplied by min weights 0.1, 0.005, 0.005
+const double kMinScaleWeights[kNumScales][3] = {
+ {0.02000, 0.00005, 0.00005}, {0.03000, 0.00025, 0.00025},
+ {0.02500, 0.00100, 0.00100}, {0.02000, 0.00150, 0.00150},
+ {0.01200, 0.00175, 0.00175}, {0.00500, 0.00175, 0.00175},
+};
+const double kEdgeWeight[3] = {1.5, 0.1, 0.1};
+const double kGridWeight[3] = {1.0, 0.1, 0.1};
+
+inline void Rgb2Lab(float r, float g, float b, float* L, float* A, float* B) {
+ const float epsilon = 0.00885645167903563081f;
+ const float s = 0.13793103448275862068f;
+ const float k = 7.78703703703703703703f;
+ float fx = (r * 0.43393624408206207259f + g * 0.37619779063650710152f +
+ b * 0.18983429773803261441f);
+ float fy = (r * 0.2126729f + g * 0.7151522f + b * 0.0721750f);
+ float fz = (r * 0.01775381083562901744f + g * 0.10945087235996326905f +
+ b * 0.87263921028466483011f);
+ const float gamma = 1.0f / 3.0f;
+ float X = (fx > epsilon) ? powf(fx, gamma) - s : k * fx;
+ float Y = (fy > epsilon) ? powf(fy, gamma) - s : k * fy;
+ float Z = (fz > epsilon) ? powf(fz, gamma) - s : k * fz;
+ *L = Y * 1.16f;
+ *A = (0.39181818181818181818f + 2.27272727272727272727f * (X - Y));
+ *B = (0.49045454545454545454f + 0.90909090909090909090f * (Y - Z));
+}
+
+Image3F Rgb2Lab(const Image3F& in) {
+ Image3F out(in.xsize(), in.ysize());
+ for (size_t y = 0; y < in.ysize(); ++y) {
+ const float* JXL_RESTRICT row_in0 = in.PlaneRow(0, y);
+ const float* JXL_RESTRICT row_in1 = in.PlaneRow(1, y);
+ const float* JXL_RESTRICT row_in2 = in.PlaneRow(2, y);
+ float* JXL_RESTRICT row_out0 = out.PlaneRow(0, y);
+ float* JXL_RESTRICT row_out1 = out.PlaneRow(1, y);
+ float* JXL_RESTRICT row_out2 = out.PlaneRow(2, y);
+
+ for (size_t x = 0; x < in.xsize(); ++x) {
+ Rgb2Lab(row_in0[x], row_in1[x], row_in2[x], &row_out0[x], &row_out1[x],
+ &row_out2[x]);
+ }
+ }
+ return out;
+}
+
+Image3F Downsample(const Image3F& in, size_t fx, size_t fy) {
+ const size_t out_xsize = (in.xsize() + fx - 1) / fx;
+ const size_t out_ysize = (in.ysize() + fy - 1) / fy;
+ Image3F out(out_xsize, out_ysize);
+ const float normalize = 1.0f / (fx * fy);
+ for (size_t c = 0; c < 3; ++c) {
+ for (size_t oy = 0; oy < out_ysize; ++oy) {
+ float* JXL_RESTRICT row_out = out.PlaneRow(c, oy);
+ for (size_t ox = 0; ox < out_xsize; ++ox) {
+ float sum = 0.0f;
+ for (size_t iy = 0; iy < fy; ++iy) {
+ for (size_t ix = 0; ix < fx; ++ix) {
+ const size_t x = std::min(ox * fx + ix, in.xsize() - 1);
+ const size_t y = std::min(oy * fy + iy, in.ysize() - 1);
+ sum += in.PlaneRow(c, y)[x];
+ }
+ }
+ row_out[ox] = sum * normalize;
+ }
+ }
+ }
+ return out;
+}
+
+void Multiply(const Image3F& a, const Image3F& b, Image3F* mul) {
+ for (size_t c = 0; c < 3; ++c) {
+ for (size_t y = 0; y < a.ysize(); ++y) {
+ const float* JXL_RESTRICT in1 = a.PlaneRow(c, y);
+ const float* JXL_RESTRICT in2 = b.PlaneRow(c, y);
+ float* JXL_RESTRICT out = mul->PlaneRow(c, y);
+ for (size_t x = 0; x < a.xsize(); ++x) {
+ out[x] = in1[x] * in2[x];
+ }
+ }
+ }
+}
+
+void RowColAvgP2(const ImageF& in, double* rp2, double* cp2) {
+ std::vector<double> ravg(in.ysize());
+ std::vector<double> cavg(in.xsize());
+ for (size_t y = 0; y < in.ysize(); ++y) {
+ auto row = in.Row(y);
+ for (size_t x = 0; x < in.xsize(); ++x) {
+ const float val = row[x];
+ ravg[y] += val;
+ cavg[x] += val;
+ }
+ }
+ std::sort(ravg.begin(), ravg.end());
+ std::sort(cavg.begin(), cavg.end());
+ *rp2 = ravg[ravg.size() / 50] / in.xsize();
+ *cp2 = cavg[cavg.size() / 50] / in.ysize();
+}
+
+class StreamingAverage {
+ public:
+ void Add(const float v) {
+ // Numerically stable method.
+ double delta = v - result_;
+ n_ += 1;
+ result_ += delta / n_;
+ }
+
+ double Get() const { return result_; }
+
+ private:
+ double result_ = 0.0;
+ size_t n_ = 0;
+};
+
+void EdgeDiffMap(const Image3F& img1, const Image3F& mu1, const Image3F& img2,
+ const Image3F& mu2, Image3F* out, double* plane_avg) {
+ for (size_t c = 0; c < 3; ++c) {
+ StreamingAverage avg;
+ for (size_t y = 0; y < img1.ysize(); ++y) {
+ const float* JXL_RESTRICT row1 = img1.PlaneRow(c, y);
+ const float* JXL_RESTRICT row2 = img2.PlaneRow(c, y);
+ const float* JXL_RESTRICT rowm1 = mu1.PlaneRow(c, y);
+ const float* JXL_RESTRICT rowm2 = mu2.PlaneRow(c, y);
+ float* JXL_RESTRICT row_out = out->PlaneRow(c, y);
+ for (size_t x = 0; x < img1.xsize(); ++x) {
+ float edgediff = std::max(
+ std::abs(row2[x] - rowm2[x]) - std::abs(row1[x] - rowm1[x]), 0.0f);
+ row_out[x] = 1.0f - edgediff;
+ avg.Add(row_out[x]);
+ }
+ }
+ plane_avg[c] = avg.Get();
+ }
+}
+
+// Temporary storage for Gaussian blur, reused for multiple images.
+class Blur {
+ public:
+ Blur(const size_t xsize, const size_t ysize)
+ : rg_(jxl::CreateRecursiveGaussian(1.5)), temp_(xsize, ysize) {}
+
+ void operator()(const ImageF& in, ImageF* JXL_RESTRICT out) {
+ jxl::ThreadPool* null_pool = nullptr;
+ FastGaussian(rg_, in, null_pool, &temp_, out);
+ }
+
+ Image3F operator()(const Image3F& in) {
+ Image3F out(in.xsize(), in.ysize());
+ operator()(in.Plane(0), &out.Plane(0));
+ operator()(in.Plane(1), &out.Plane(1));
+ operator()(in.Plane(2), &out.Plane(2));
+ return out;
+ }
+
+ // Allows reusing across scales.
+ void ShrinkTo(const size_t xsize, const size_t ysize) {
+ temp_.ShrinkTo(xsize, ysize);
+ }
+
+ private:
+ hwy::AlignedUniquePtr<jxl::RecursiveGaussian> rg_;
+ ImageF temp_;
+};
+
+void SSIMMap(const Image3F& m1, const Image3F& m2, const Image3F& s11,
+ const Image3F& s22, const Image3F& s12, Image3F* out,
+ double* plane_averages) {
+ for (size_t c = 0; c < 3; ++c) {
+ StreamingAverage avg;
+ for (size_t y = 0; y < out->ysize(); ++y) {
+ const float* JXL_RESTRICT row_m1 = m1.PlaneRow(c, y);
+ const float* JXL_RESTRICT row_m2 = m2.PlaneRow(c, y);
+ const float* JXL_RESTRICT row_s11 = s11.PlaneRow(c, y);
+ const float* JXL_RESTRICT row_s22 = s22.PlaneRow(c, y);
+ const float* JXL_RESTRICT row_s12 = s12.PlaneRow(c, y);
+ float* JXL_RESTRICT row_out = out->PlaneRow(c, y);
+ for (size_t x = 0; x < out->xsize(); ++x) {
+ float mu1 = row_m1[x];
+ float mu2 = row_m2[x];
+ float mu11 = mu1 * mu1;
+ float mu22 = mu2 * mu2;
+ float mu12 = mu1 * mu2;
+ float nom_m = 2 * mu12 + kC1;
+ float nom_s = 2 * (row_s12[x] - mu12) + kC2;
+ float denom_m = mu11 + mu22 + kC1;
+ float denom_s = (row_s11[x] - mu11) + (row_s22[x] - mu22) + kC2;
+ row_out[x] = (nom_m * nom_s) / (denom_m * denom_s);
+ avg.Add(row_out[x]);
+ }
+ }
+ plane_averages[c] = avg.Get();
+ }
+}
+
+} // namespace
+
+double Ssimulacra::Score() const {
+ double ssim = 0.0;
+ double ssim_max = 0.0;
+ for (size_t c = 0; c < 3; ++c) {
+ for (size_t scale = 0; scale < scales.size(); ++scale) {
+ ssim += kScaleWeights[scale][c] * scales[scale].avg_ssim[c];
+ ssim_max += kScaleWeights[scale][c];
+ ssim += kMinScaleWeights[scale][c] * scales[scale].min_ssim[c];
+ ssim_max += kMinScaleWeights[scale][c];
+ }
+ if (!simple) {
+ ssim += kEdgeWeight[c] * avg_edgediff[c];
+ ssim_max += kEdgeWeight[c];
+ ssim += kGridWeight[c] *
+ (row_p2[0][c] + row_p2[1][c] + col_p2[0][c] + col_p2[1][c]);
+ ssim_max += 4.0 * kGridWeight[c];
+ }
+ }
+ double dssim = ssim_max / ssim - 1.0;
+ return std::min(1.0, std::max(0.0, dssim));
+}
+
+inline void PrintItem(const char* name, int scale, const double* vals,
+ const double* w) {
+ printf("scale %d %s = [%.10f %.10f %.10f] w = [%.5f %.5f %.5f]\n", scale,
+ name, vals[0], vals[1], vals[2], w[0], w[1], w[2]);
+}
+
+void Ssimulacra::PrintDetails() const {
+ for (size_t s = 0; s < scales.size(); ++s) {
+ if (s < kNumScales) {
+ PrintItem("avg ssim", s, scales[s].avg_ssim, kScaleWeights[s]);
+ PrintItem("min ssim", s, scales[s].min_ssim, kMinScaleWeights[s]);
+ }
+ if (s == 0 && !simple) {
+ PrintItem("avg edif", s, avg_edgediff, kEdgeWeight);
+ PrintItem("rp2 ssim", s, &row_p2[0][0], kGridWeight);
+ PrintItem("cp2 ssim", s, &col_p2[0][0], kGridWeight);
+ PrintItem("rp2 edif", s, &row_p2[1][0], kGridWeight);
+ PrintItem("cp2 edif", s, &col_p2[1][0], kGridWeight);
+ }
+ }
+}
+
+Ssimulacra ComputeDiff(const Image3F& orig, const Image3F& distorted,
+ bool simple) {
+ Ssimulacra ssimulacra;
+
+ ssimulacra.simple = simple;
+ Image3F img1 = Rgb2Lab(orig);
+ Image3F img2 = Rgb2Lab(distorted);
+
+ Image3F mul(orig.xsize(), orig.ysize());
+ Blur blur(img1.xsize(), img1.ysize());
+
+ for (int scale = 0; scale < kNumScales; scale++) {
+ if (img1.xsize() < 8 || img1.ysize() < 8) {
+ break;
+ }
+ if (scale) {
+ img1 = Downsample(img1, 2, 2);
+ img2 = Downsample(img2, 2, 2);
+ }
+ mul.ShrinkTo(img1.xsize(), img2.ysize());
+ blur.ShrinkTo(img1.xsize(), img2.ysize());
+
+ Multiply(img1, img1, &mul);
+ Image3F sigma1_sq = blur(mul);
+
+ Multiply(img2, img2, &mul);
+ Image3F sigma2_sq = blur(mul);
+
+ Multiply(img1, img2, &mul);
+ Image3F sigma12 = blur(mul);
+
+ Image3F mu1 = blur(img1);
+ Image3F mu2 = blur(img2);
+ // Reuse mul as "ssim_map".
+ SsimulacraScale sscale;
+ SSIMMap(mu1, mu2, sigma1_sq, sigma2_sq, sigma12, &mul, sscale.avg_ssim);
+
+ const Image3F ssim_map = Downsample(mul, 4, 4);
+ for (size_t c = 0; c < 3; c++) {
+ float minval, maxval;
+ ImageMinMax(ssim_map.Plane(c), &minval, &maxval);
+ sscale.min_ssim[c] = static_cast<double>(minval);
+ }
+ ssimulacra.scales.push_back(sscale);
+
+ if (scale == 0 && !simple) {
+ Image3F* edgediff = &sigma1_sq; // reuse
+ EdgeDiffMap(img1, mu1, img2, mu2, edgediff, ssimulacra.avg_edgediff);
+ for (size_t c = 0; c < 3; c++) {
+ RowColAvgP2(ssim_map.Plane(c), &ssimulacra.row_p2[0][c],
+ &ssimulacra.col_p2[0][c]);
+ RowColAvgP2(edgediff->Plane(c), &ssimulacra.row_p2[1][c],
+ &ssimulacra.col_p2[1][c]);
+ }
+ }
+ }
+ return ssimulacra;
+}
+
+} // namespace ssimulacra