get_disto: add a '-o file' option to save a diff map

also: -scale option is useful for using the maximum range.

Change-Id: I8ede7132b08ece7d3b6f699b710ab2ef3fb0b734

extras/get_disto.c

@@ -47,6 +47,35 @@ static size_t ReadPicture(const char* const filename, WebPPicture* const pic,
   return ok ? data_size : 0;
 }
 
+// returns the max absolute difference
+static int DiffScaleChannel(uint8_t* src1, int stride1,
+                            const uint8_t* src2, int stride2,
+                            int x_stride, int w, int h, int do_scaling) {
+  int x, y;
+  uint32_t max = 1;
+  for (y = 0; y < h; ++y) {
+    uint8_t* const ptr1 = src1 + y * stride1;
+    const uint8_t* const ptr2 = src2 + y * stride2;
+    for (x = 0; x < w * x_stride; x += x_stride) {
+      const uint32_t diff = abs(ptr1[x] - ptr2[x]);
+      if (diff > max) max = diff;
+      ptr1[x] = diff;
+    }
+  }
+
+  if (do_scaling) {
+    const uint32_t factor = (255u << 16) / max;
+    for (y = 0; y < h; ++y) {
+      uint8_t* const ptr1 = src1 + y * stride1;
+      for (x = 0; x < w * x_stride; x += x_stride) {
+        const uint32_t diff = (ptr1[x] * factor) >> 16;
+        ptr1[x] = diff;
+      }
+    }
+  }
+  return max;
+}
+
 static void Help(void) {
   fprintf(stderr,
           "Usage: get_disto [-ssim][-psnr][-alpha] compressed.webp orig.webp\n"
@@ -54,6 +83,8 @@ static void Help(void) {
           "  -psnr ..... print PSNR distortion (default)\n"
           "  -alpha .... preserve alpha plane\n"
           "  -h ........ this message\n"
+          "  -o <file> . save the diff map as a WebP lossless file\n"
+          "  -scale .... scale the difference map to fit [0..255] range\n"
           " Also handles PNG, JPG and TIFF files, in addition to WebP.\n");
 }
 
@@ -66,8 +97,10 @@ int main(int argc, const char *argv[]) {
   int c;
   int help = 0;
   int keep_alpha = 0;
+  int scale = 0;
   const char* name1 = NULL;
   const char* name2 = NULL;
+  const char* output = NULL;
 
   if (!WebPPictureInit(&pic1) || !WebPPictureInit(&pic2)) {
     fprintf(stderr, "Can't init pictures\n");
@@ -81,9 +114,17 @@ int main(int argc, const char *argv[]) {
       type = 0;
     } else if (!strcmp(argv[c], "-alpha")) {
       keep_alpha = 1;
+    } else if (!strcmp(argv[c], "-scale")) {
+      scale = 1;
     } else if (!strcmp(argv[c], "-h")) {
       help = 1;
       ret = 0;
+    } else if (!strcmp(argv[c], "-o")) {
+      if (++c == argc) {
+        fprintf(stderr, "missing file name after %s option.\n", argv[c - 1]);
+        goto End;
+      }
+      output = argv[c];
     } else if (name1 == NULL) {
       name1 = argv[c];
     } else {
@@ -115,6 +156,43 @@ int main(int argc, const char *argv[]) {
   printf("%u %.2f    %.2f %.2f %.2f %.2f\n",
          (unsigned int)size1, disto[4],
          disto[0], disto[1], disto[2], disto[3]);
+
+  if (output != NULL) {
+    uint8_t* data = NULL;
+    size_t data_size = 0;
+    if (pic1.use_argb != pic1.use_argb) {
+      fprintf(stderr, "Pictures are not in the same argb format. "
+                      "Can't save the difference map.\n");
+      goto End;
+    }
+    if (pic1.use_argb) {
+      int n;
+      fprintf(stderr, "max absolute differences per channel: ");
+      for (n = 0; n < 3; ++n) {    // skip the alpha channel
+        const int range = DiffScaleChannel((uint8_t*)pic1.argb + n,
+                                           pic1.argb_stride * 4,
+                                           (const uint8_t*)pic2.argb + n,
+                                           pic2.argb_stride * 4,
+                                           4, pic1.width, pic1.height, scale);
+        fprintf(stderr, "[%d]", range);
+      }
+      fprintf(stderr, "\n");
+    } else {
+      fprintf(stderr, "Can only compute the difference map in ARGB format.\n");
+      goto End;
+    }
+    data_size = WebPEncodeLosslessBGRA((const uint8_t*)pic1.argb,
+                                       pic1.width, pic1.height,
+                                       pic1.argb_stride * 4,
+                                       &data);
+    if (data_size == 0) {
+      fprintf(stderr, "Error during lossless encoding.\n");
+      goto End;
+    }
+    ret = ImgIoUtilWriteFile(output, data, data_size) ? 0 : 1;
+    WebPFree(data);
+    if (ret) goto End;
+  }
   ret = 0;
 
  End: