add -print_psnr and -print_ssim options to cwebp.

These will report the 7x7-averaged PSNR or SSIM, using the
new internal function WebPPictureDistortion().
This is for information only. These flags have no encoding impact.

+misc opportunistic cosmetics

Change-Id: I64c0a7eca679134d39062e438886274b22bb643f

README

@@ -148,6 +148,8 @@ options:
   -crop <x> <y> <w> <h> .. crop picture with the given rectangle
   -resize <w> <h> ........ resize picture (after any cropping)
   -map <int> ............. print map of extra info.
+  -print_ssim ............ prints averaged SSIM distortion.
+  -print_psnr ............ prints averaged PSNR distortion.
   -d <file.pgm> .......... dump the compressed output (PGM file).
   -alpha_method <int> .... Transparency-compression method (0..1)
   -alpha_filter <string> . predictive filtering for alpha plane.

examples/cwebp.c

@@ -529,7 +529,8 @@ static void PrintValues(const int values[4]) {
   fprintf(stderr, "|\n");
 }
 
-static void PrintExtraInfo(const WebPPicture* const pic, int short_output) {
+static void PrintExtraInfo(const WebPPicture* const pic, int short_output,
+                           const char* const file_name) {
   const WebPAuxStats* const stats = pic->stats;
   if (short_output) {
     fprintf(stderr, "%7d %2.2f\n", stats->coded_size, stats->PSNR[3]);
@@ -538,8 +539,11 @@ static void PrintExtraInfo(const WebPPicture* const pic, int short_output) {
     const int num_i16 = stats->block_count[1];
     const int num_skip = stats->block_count[2];
     const int total = num_i4 + num_i16;
-    fprintf(stderr,
+    fprintf(stderr, "File:      %s\n", file_name);
-            "%7d bytes Y-U-V-All-PSNR %2.2f %2.2f %2.2f   %2.2f dB\n",
+    fprintf(stderr, "Dimension: %d x %d%s\n",
+            pic->width, pic->height, (pic->a != NULL) ? " (with alpha)" : "");
+    fprintf(stderr, "Output:    "
+            "%d bytes Y-U-V-All-PSNR %2.2f %2.2f %2.2f   %2.2f dB\n",
             stats->coded_size,
             stats->PSNR[0], stats->PSNR[1], stats->PSNR[2], stats->PSNR[3]);
     if (total > 0) {
@@ -626,7 +630,7 @@ static int DumpPicture(const WebPPicture* const picture, const char* PGM_name) {
   const int alpha_height = picture->a ? picture->height : 0;
   const int height = picture->height + uv_height + alpha_height;
   FILE* const f = fopen(PGM_name, "wb");
-  if (!f) return 0;
+  if (f == NULL) return 0;
   fprintf(f, "P5\n%d %d\n255\n", stride, height);
   for (y = 0; y < picture->height; ++y) {
     if (fwrite(picture->y + y * picture->y_stride, picture->width, 1, f) != 1)
@@ -707,6 +711,8 @@ static void HelpLong(void) {
   printf("  -444 / -422 / -gray ..... Change colorspace\n");
 #endif
   printf("  -map <int> ............. print map of extra info.\n");
+  printf("  -print_ssim ............ prints averaged SSIM distortion.\n");
+  printf("  -print_psnr ............ prints averaged PSNR distortion.\n");
   printf("  -d <file.pgm> .......... dump the compressed output (PGM file).\n");
   printf("  -alpha_method <int> .... Transparency-compression method (0..1)\n");
   printf("  -alpha_filter <string> . predictive filtering for alpha plane.\n");
@@ -766,11 +772,15 @@ int main(int argc, const char *argv[]) {
   int resize_w = 0, resize_h = 0;
   int show_progress = 0;
   WebPPicture picture;
+  int print_distortion = 0;        // 1=PSNR, 2=SSIM
+  WebPPicture original_picture;    // when PSNR or SSIM is requested
   WebPConfig config;
   WebPAuxStats stats;
   Stopwatch stop_watch;
 
-  if (!WebPPictureInit(&picture) || !WebPConfigInit(&config)) {
+  if (!WebPPictureInit(&picture) ||
+      !WebPPictureInit(&original_picture) ||
+      !WebPConfigInit(&config)) {
     fprintf(stderr, "Error! Version mismatch!\n");
     goto Error;
   }
@@ -792,6 +802,12 @@ int main(int argc, const char *argv[]) {
     } else if (!strcmp(argv[c], "-d") && c < argc - 1) {
       dump_file = argv[++c];
       config.show_compressed = 1;
+    } else if (!strcmp(argv[c], "-print_ssim")) {
+      config.show_compressed = 1;
+      print_distortion = 2;
+    } else if (!strcmp(argv[c], "-print_psnr")) {
+      config.show_compressed = 1;
+      print_distortion = 1;
     } else if (!strcmp(argv[c], "-short")) {
       short_output++;
     } else if (!strcmp(argv[c], "-s") && c < argc - 2) {
@@ -919,7 +935,7 @@ int main(int argc, const char *argv[]) {
     StopwatchReadAndReset(&stop_watch);
   }
   if (!ReadPicture(in_file, &picture, keep_alpha)) {
-    fprintf(stderr, "Error! Cannot read input picture\n");
+    fprintf(stderr, "Error! Cannot read input picture file '%s'\n", in_file);
     goto Error;
   }
   picture.progress_hook = (show_progress && !quiet) ? ProgressReport : NULL;
@@ -932,7 +948,7 @@ int main(int argc, const char *argv[]) {
   // Open the output
   if (out_file) {
     out = fopen(out_file, "wb");
-    if (!out) {
+    if (out == NULL) {
       fprintf(stderr, "Error! Cannot open output file '%s'\n", out_file);
       goto Error;
     } else {
@@ -969,6 +985,9 @@ int main(int argc, const char *argv[]) {
   if (picture.extra_info_type > 0) {
     AllocExtraInfo(&picture);
   }
+  if (print_distortion > 0) {  // Save original picture for later comparison
+    WebPPictureCopy(&picture, &original_picture);
+  }
   if (!WebPEncode(&config, &picture)) {
     fprintf(stderr, "Error! Cannot encode picture as WebP\n");
     fprintf(stderr, "Error code: %d (%s)\n",
@@ -984,13 +1003,23 @@ int main(int argc, const char *argv[]) {
   if (dump_file) {
     DumpPicture(&picture, dump_file);
   }
+
   if (!quiet) {
-    PrintExtraInfo(&picture, short_output);
+    PrintExtraInfo(&picture, short_output, in_file);
+  }
+  if (!quiet && !short_output && print_distortion > 0) {  // print distortion
+    float values[5];
+    WebPPictureDistortion(&picture, &original_picture,
+                          (print_distortion == 1) ? 0 : 1, values);
+    fprintf(stderr, "%s: Y:%.2f U:%.2f V:%.2f A:%.2f  Total:%.2f\n",
+            (print_distortion == 1) ? "PSNR" : "SSIM",
+            values[0], values[1], values[2], values[3], values[4]);
   }
 
  Error:
   free(picture.extra_info);
   WebPPictureFree(&picture);
+  WebPPictureFree(&original_picture);
   if (out != NULL) {
     fclose(out);
   }

man/cwebp.1

@@ -168,6 +168,12 @@ Disable all assembly optimizations.
 .B \-v
 Print extra information (encoding time in particular).
 .TP
+.B \-print_psnr
+Compute and report average PSNR (Peak-Signal-To-Noise ratio).
+.TP
+.B \-print_ssim
+Compute and report average SSIM (structural similarity metric)
+.TP
 .B \-progress
 Report encoding progress in percent.
 .TP

src/enc/filter.c

@@ -234,14 +234,21 @@ static void DoFilter(const VP8EncIterator* const it, int level) {
 // SSIM metric
 
 enum { KERNEL = 3 };
-typedef struct {
+static const double kMinValue = 1.e-10;  // minimal threshold
-  double w, xm, ym, xxm, xym, yym;
-} SSIMStats;
 
-static void Accumulate(const uint8_t* src1, int stride1,
+void VP8SSIMAddStats(const DistoStats* const src, DistoStats* const dst) {
+  dst->w   += src->w;
+  dst->xm  += src->xm;
+  dst->ym  += src->ym;
+  dst->xxm += src->xxm;
+  dst->xym += src->xym;
+  dst->yym += src->yym;
+}
+
+static void VP8SSIMAccumulate(const uint8_t* src1, int stride1,
                               const uint8_t* src2, int stride2,
                               int xo, int yo, int W, int H,
-                       SSIMStats* const stats) {
+                              DistoStats* const stats) {
   const int ymin = (yo - KERNEL < 0) ? 0 : yo - KERNEL;
   const int ymax = (yo + KERNEL > H - 1) ? H - 1 : yo + KERNEL;
   const int xmin = (xo - KERNEL < 0) ? 0 : xo - KERNEL;
@@ -263,7 +270,7 @@ static void Accumulate(const uint8_t* src1, int stride1,
   }
 }
 
-static double GetSSIM(const SSIMStats* const stats) {
+double VP8SSIMGet(const DistoStats* const stats) {
   const double xmxm = stats->xm * stats->xm;
   const double ymym = stats->ym * stats->ym;
   const double xmym = stats->xm * stats->ym;
@@ -281,26 +288,49 @@ static double GetSSIM(const SSIMStats* const stats) {
   C2 = 58.5225 * w2;
   fnum = (2 * xmym + C1) * (2 * sxy + C2);
   fden = (xmxm + ymym + C1) * (sxx + syy + C2);
-  return (fden != 0) ? fnum / fden : 0.;
+  return (fden != 0.) ? fnum / fden : kMinValue;
+}
+
+double VP8SSIMGetSquaredError(const DistoStats* const s) {
+  if (s->w > 0.) {
+    const double iw2 = 1. / (s->w * s->w);
+    const double sxx = s->xxm * s->w - s->xm * s->xm;
+    const double syy = s->yym * s->w - s->ym * s->ym;
+    const double sxy = s->xym * s->w - s->xm * s->ym;
+    const double SSE = iw2 * (sxx + syy - 2. * sxy);
+    if (SSE > kMinValue) return SSE;
+  }
+  return kMinValue;
+}
+
+void VP8SSIMAccumulatePlane(const uint8_t* src1, int stride1,
+                            const uint8_t* src2, int stride2,
+                            int W, int H, DistoStats* const stats) {
+  int x, y;
+  for (y = 0; y < H; ++y) {
+    for (x = 0; x < W; ++x) {
+      VP8SSIMAccumulate(src1, stride1, src2, stride2, x, y, W, H, stats);
+    }
+  }
 }
 
 static double GetMBSSIM(const uint8_t* yuv1, const uint8_t* yuv2) {
   int x, y;
-  SSIMStats s = { .0, .0, .0, .0, .0, .0 };
+  DistoStats s = { .0, .0, .0, .0, .0, .0 };
 
   // compute SSIM in a 10 x 10 window
   for (x = 3; x < 13; x++) {
     for (y = 3; y < 13; y++) {
-      Accumulate(yuv1 + Y_OFF, BPS, yuv2 + Y_OFF, BPS, x, y, 16, 16, &s);
+      VP8SSIMAccumulate(yuv1 + Y_OFF, BPS, yuv2 + Y_OFF, BPS, x, y, 16, 16, &s);
     }
   }
   for (x = 1; x < 7; x++) {
     for (y = 1; y < 7; y++) {
-      Accumulate(yuv1 + U_OFF, BPS, yuv2 + U_OFF, BPS, x, y, 8, 8, &s);
+      VP8SSIMAccumulate(yuv1 + U_OFF, BPS, yuv2 + U_OFF, BPS, x, y, 8, 8, &s);
-      Accumulate(yuv1 + V_OFF, BPS, yuv2 + V_OFF, BPS, x, y, 8, 8, &s);
+      VP8SSIMAccumulate(yuv1 + V_OFF, BPS, yuv2 + V_OFF, BPS, x, y, 8, 8, &s);
     }
   }
-  return GetSSIM(&s);
+  return VP8SSIMGet(&s);
 }
 
 //------------------------------------------------------------------------------

src/enc/picture.c

@@ -11,6 +11,7 @@
 
 #include <assert.h>
 #include <stdlib.h>
+#include <math.h>
 
 #include "./vp8enci.h"
 
@@ -659,7 +660,58 @@ void WebPCleanupTransparentArea(WebPPicture* const pic) {
 #undef SIZE2
 
 //------------------------------------------------------------------------------
-// Simplest call:
+// Distortion
+
+// Max value returned in case of exact similarity.
+static const double kMinDistortion_dB = 99.;
+
+int WebPPictureDistortion(const WebPPicture* const pic1,
+                          const WebPPicture* const pic2,
+                          int type, float result[5]) {
+  int c;
+  DistoStats stats[5];
+
+  if (pic1->width != pic2->width ||
+      pic1->height != pic2->height ||
+      (pic1->a == NULL) != (pic2->a == NULL)) {
+    return 0;
+  }
+
+  memset(stats, 0, sizeof(stats));
+  VP8SSIMAccumulatePlane(pic1->y, pic1->y_stride,
+                         pic2->y, pic2->y_stride,
+                         pic1->width, pic1->height, &stats[0]);
+  VP8SSIMAccumulatePlane(pic1->u, pic1->uv_stride,
+                         pic2->u, pic2->uv_stride,
+                         (pic1->width + 1) >> 1, (pic1->height + 1) >> 1,
+                         &stats[1]);
+  VP8SSIMAccumulatePlane(pic1->v, pic1->uv_stride,
+                         pic2->v, pic2->uv_stride,
+                         (pic1->width + 1) >> 1, (pic1->height + 1) >> 1,
+                         &stats[2]);
+  if (pic1->a != NULL) {
+    VP8SSIMAccumulatePlane(pic1->a, pic1->a_stride,
+                           pic2->a, pic2->a_stride,
+                           pic1->width, pic1->height, &stats[3]);
+  }
+  for (c = 0; c <= 4; ++c) {
+    if (type == 1) {
+      const double v = VP8SSIMGet(&stats[c]);
+      result[c] = (v < 1.) ? -10.0 * log10(1. - v)
+                           : kMinDistortion_dB;
+    } else {
+      const double v = VP8SSIMGetSquaredError(&stats[c]);
+      result[c] = (v > 0.) ? -4.3429448 * log(v / (255 * 255.))
+                           : kMinDistortion_dB;
+    }
+    // Accumulate forward
+    if (c < 4) VP8SSIMAddStats(&stats[c], &stats[4]);
+  }
+  return 1;
+}
+
+//------------------------------------------------------------------------------
+// Simplest high-level calls:
 
 typedef int (*Importer)(WebPPicture* const, const uint8_t* const, int);
 

src/enc/vp8enci.h

@@ -455,9 +455,20 @@ int VP8EncFinishLayer(VP8Encoder* const enc);    // finalize coding
 void VP8EncDeleteLayer(VP8Encoder* enc);         // reclaim memory
 
   // in filter.c
-extern void VP8InitFilter(VP8EncIterator* const it);
+
-extern void VP8StoreFilterStats(VP8EncIterator* const it);
+// SSIM utils
-extern void VP8AdjustFilterStrength(VP8EncIterator* const it);
+typedef struct { double w, xm, ym, xxm, xym, yym; } DistoStats;
+void VP8SSIMAddStats(const DistoStats* const src, DistoStats* const dst);
+void VP8SSIMAccumulatePlane(const uint8_t* src1, int stride1,
+                            const uint8_t* src2, int stride2,
+                            int W, int H, DistoStats* const stats);
+double VP8SSIMGet(const DistoStats* const stats);
+double VP8SSIMGetSquaredError(const DistoStats* const stats);
+
+// autofilter
+void VP8InitFilter(VP8EncIterator* const it);
+void VP8StoreFilterStats(VP8EncIterator* const it);
+void VP8AdjustFilterStrength(VP8EncIterator* const it);
 
 //------------------------------------------------------------------------------
 

src/webp/encode.h

@@ -248,6 +248,15 @@ WEBP_EXTERN(void) WebPPictureFree(WebPPicture* const picture);
 WEBP_EXTERN(int) WebPPictureCopy(const WebPPicture* const src,
                                  WebPPicture* const dst);
 
+// Compute PSNR or SSIM distortion between two pictures.
+// Result is in dB, stores in result[] in the Y/U/V/Alpha/All order.
+// Returns 0 in case of error (pic1 and pic2 don't have same dimension, ...)
+// Warning: this function is rather CPU-intensive.
+WEBP_EXTERN(int) WebPPictureDistortion(
+    const WebPPicture* const pic1, const WebPPicture* const pic2,
+    int metric_type,           // 0 = PSNR, 1 = SSIM
+    float result[5]);
+
 // self-crops a picture to the rectangle defined by top/left/width/height.
 // Returns 0 in case of memory allocation error, or if the rectangle is
 // outside of the source picture.