Merge changes I25711dd5,I43188fab

* changes:
  Fix assertions in WebPRescalerExportRow()
  Add descriptions of default configuration in help info.

README

@@ -220,8 +220,9 @@ assumed to be a PNG, JPEG, TIFF or WebP file.
 Options:
   -h / -help ............. short help
   -H / -longhelp ......... long help
-  -q <float> ............. quality factor (0:small..100:big)
+  -q <float> ............. quality factor (0:small..100:big), default=75
-  -alpha_q <int> ......... transparency-compression quality (0..100)
+  -alpha_q <int> ......... transparency-compression quality (0..100),
+                           default=100
   -preset <string> ....... preset setting, one of:
                             default, photo, picture,
                             drawing, icon, text
@@ -229,15 +230,15 @@ Options:
   -z <int> ............... activates lossless preset with given
                            level in [0:fast, ..., 9:slowest]
 
-  -m <int> ............... compression method (0=fast, 6=slowest)
+  -m <int> ............... compression method (0=fast, 6=slowest), default=4
-  -segments <int> ........ number of segments to use (1..4)
+  -segments <int> ........ number of segments to use (1..4), default=4
   -size <int> ............ target size (in bytes)
   -psnr <float> .......... target PSNR (in dB. typically: 42)
 
   -s <int> <int> ......... input size (width x height) for YUV
-  -sns <int> ............. spatial noise shaping (0:off, 100:max)
+  -sns <int> ............. spatial noise shaping (0:off, 100:max), default=50
-  -f <int> ............... filter strength (0=off..100)
+  -f <int> ............... filter strength (0=off..100), default=60
-  -sharpness <int> ....... filter sharpness (0:most .. 7:least sharp)
+  -sharpness <int> ....... filter sharpness (0:most .. 7:least sharp), default=0
   -strong ................ use strong filter instead of simple (default)
   -nostrong .............. use simple filter instead of strong
   -partition_limit <int> . limit quality to fit the 512k limit on
@@ -252,18 +253,18 @@ Options:
   -print_ssim ............ prints averaged SSIM distortion
   -print_lsim ............ prints local-similarity distortion
   -d <file.pgm> .......... dump the compressed output (PGM file)
-  -alpha_method <int> .... transparency-compression method (0..1)
+  -alpha_method <int> .... transparency-compression method (0..1), default=1
   -alpha_filter <string> . predictive filtering for alpha plane,
                            one of: none, fast (default) or best
-  -exact ................. preserve RGB values in transparent area
+  -exact ................. preserve RGB values in transparent area, default=off
   -blend_alpha <hex> ..... blend colors against background color
                            expressed as RGB values written in
                            hexadecimal, e.g. 0xc0e0d0 for red=0xc0
                            green=0xe0 and blue=0xd0
   -noalpha ............... discard any transparency information
-  -lossless .............. encode image losslessly
+  -lossless .............. encode image losslessly, default=off
   -near_lossless <int> ... use near-lossless image
-                           preprocessing (0..100=off)
+                           preprocessing (0..100=off), default=100
   -hint <string> ......... specify image characteristics hint,
                            one of: photo, picture or graph
 

examples/cwebp.c

@@ -521,9 +521,10 @@ static void HelpLong(void) {
   printf("\nOptions:\n");
   printf("  -h / -help ............. short help\n");
   printf("  -H / -longhelp ......... long help\n");
-  printf("  -q <float> ............. quality factor (0:small..100:big)\n");
+  printf("  -q <float> ............. quality factor (0:small..100:big), "
-  printf("  -alpha_q <int> ......... transparency-compression quality "
+         "default=75\n");
-         "(0..100)\n");
+  printf("  -alpha_q <int> ......... transparency-compression quality (0..100),"
+         "\n                           default=100\n");
   printf("  -preset <string> ....... preset setting, one of:\n");
   printf("                            default, photo, picture,\n");
   printf("                            drawing, icon, text\n");
@@ -531,16 +532,20 @@ static void HelpLong(void) {
   printf("  -z <int> ............... activates lossless preset with given\n"
          "                           level in [0:fast, ..., 9:slowest]\n");
   printf("\n");
-  printf("  -m <int> ............... compression method (0=fast, 6=slowest)\n");
+  printf("  -m <int> ............... compression method (0=fast, 6=slowest), "
-  printf("  -segments <int> ........ number of segments to use (1..4)\n");
+         "default=4\n");
+  printf("  -segments <int> ........ number of segments to use (1..4), "
+         "default=4\n");
   printf("  -size <int> ............ target size (in bytes)\n");
   printf("  -psnr <float> .......... target PSNR (in dB. typically: 42)\n");
   printf("\n");
   printf("  -s <int> <int> ......... input size (width x height) for YUV\n");
-  printf("  -sns <int> ............. spatial noise shaping (0:off, 100:max)\n");
+  printf("  -sns <int> ............. spatial noise shaping (0:off, 100:max), "
-  printf("  -f <int> ............... filter strength (0=off..100)\n");
+         "default=50\n");
+  printf("  -f <int> ............... filter strength (0=off..100), "
+         "default=60\n");
   printf("  -sharpness <int> ....... "
-         "filter sharpness (0:most .. 7:least sharp)\n");
+         "filter sharpness (0:most .. 7:least sharp), default=0\n");
   printf("  -strong ................ use strong filter instead "
                                      "of simple (default)\n");
   printf("  -nostrong .............. use simple filter instead of strong\n");
@@ -557,19 +562,21 @@ static void HelpLong(void) {
   printf("  -print_ssim ............ prints averaged SSIM distortion\n");
   printf("  -print_lsim ............ prints local-similarity 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_method <int> .... transparency-compression method (0..1), "
+         "default=1\n");
   printf("  -alpha_filter <string> . predictive filtering for alpha plane,\n");
   printf("                           one of: none, fast (default) or best\n");
-  printf("  -exact ................. preserve RGB values in transparent area"
+  printf("  -exact ................. preserve RGB values in transparent area, "
-         "\n");
+         "default=off\n");
   printf("  -blend_alpha <hex> ..... blend colors against background color\n"
          "                           expressed as RGB values written in\n"
          "                           hexadecimal, e.g. 0xc0e0d0 for red=0xc0\n"
          "                           green=0xe0 and blue=0xd0\n");
   printf("  -noalpha ............... discard any transparency information\n");
-  printf("  -lossless .............. encode image losslessly\n");
+  printf("  -lossless .............. encode image losslessly, default=off\n");
   printf("  -near_lossless <int> ... use near-lossless image\n"
-         "                           preprocessing (0..100=off)\n");
+         "                           preprocessing (0..100=off), "
+         "default=100\n");
 #ifdef WEBP_EXPERIMENTAL_FEATURES
   printf("  -delta_palettization ... use delta palettization\n");
 #endif  // WEBP_EXPERIMENTAL_FEATURES

man/cwebp.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH CWEBP 1 "June 23, 2016"
+.TH CWEBP 1 "August 05, 2016"
 .SH NAME
 cwebp \- compress an image file to a WebP file
 .SH SYNOPSIS
@@ -171,7 +171,7 @@ Specify the amplitude of the spatial noise shaping. Spatial noise shaping
 (or \fBsns\fP for short) refers to a general collection of built\-in algorithms
 used to decide which area of the picture should use relatively less bits,
 and where else to better transfer these bits. The possible range goes from
-0 (algorithm is off) to 100 (the maximal effect). The default value is 80.
+0 (algorithm is off) to 100 (the maximal effect). The default value is 50.
 .TP
 .BI \-segments " int
 Change the number of partitions to use during the segmentation of the

src/dsp/rescaler.c

@@ -173,10 +173,10 @@ void WebPRescalerExportRow(WebPRescaler* const wrk) {
       WebPRescalerExportRowExpand(wrk);
     } else if (wrk->fxy_scale) {
       WebPRescalerExportRowShrink(wrk);
-    } else {  // very special case for src = dst = 1x1
+    } else {  // special case
       int i;
+      assert(wrk->src_height == wrk->dst_height && wrk->x_add == 1);
       assert(wrk->src_width == 1 && wrk->dst_width <= 2);
-      assert(wrk->src_height == 1 && wrk->dst_height == 1);
       for (i = 0; i < wrk->num_channels * wrk->dst_width; ++i) {
         wrk->dst[i] = wrk->irow[i];
         wrk->irow[i] = 0;

src/utils/rescaler.c

@@ -48,11 +48,15 @@ void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
   wrk->y_sub = wrk->y_expand ? y_sub - 1 : y_sub;
   wrk->y_accum = wrk->y_expand ? wrk->y_sub : wrk->y_add;
   if (!wrk->y_expand) {
-    // this is WEBP_RESCALER_FRAC(dst_height, x_add * y_add) without the cast.
+    // This is WEBP_RESCALER_FRAC(dst_height, x_add * y_add) without the cast.
+    // Its value is <= WEBP_RESCALER_ONE, because dst_height <= wrk->y_add, and
+    // wrk->x_add >= 1;
     const uint64_t ratio =
         (uint64_t)dst_height * WEBP_RESCALER_ONE / (wrk->x_add * wrk->y_add);
     if (ratio != (uint32_t)ratio) {
-      // We can't represent the ratio with the current fixed-point precision.
+      // When ratio == WEBP_RESCALER_ONE, we can't represent the ratio with the
+      // current fixed-point precision. This happens when src_height ==
+      // wrk->y_add (which == src_height), and wrk->x_add == 1.
       // => We special-case fxy_scale = 0, in WebPRescalerExportRow().
       wrk->fxy_scale = 0;
     } else {