cwebp: add a -sharp_yuv option for 'sharp' RGB->YUV conversion

Change-Id: I6edd5b44d693da50f702fa8218f14872874d91ba

README

@@ -241,6 +241,7 @@ Options:
   -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
+  -sharp_yuv ............. use sharper (and slower) RGB->YUV conversion
   -partition_limit <int> . limit quality to fit the 512k limit on
                            the first partition (0=no degradation ... 100=full)
   -pass <int> ............ analysis pass number (1..10)

examples/cwebp.c

@@ -549,6 +549,8 @@ static void HelpLong(void) {
   printf("  -strong ................ use strong filter instead "
                                      "of simple (default)\n");
   printf("  -nostrong .............. use simple filter instead of strong\n");
+  printf("  -sharp_yuv ............. use sharper (and slower) RGB->YUV "
+                                     "conversion\n");
   printf("  -partition_limit <int> . limit quality to fit the 512k limit on\n");
   printf("                           "
          "the first partition (0=no degradation ... 100=full)\n");
@@ -787,6 +789,8 @@ int main(int argc, const char *argv[]) {
       config.filter_type = 0;
     } else if (!strcmp(argv[c], "-sharpness") && c < argc - 1) {
       config.filter_sharpness = ExUtilGetInt(argv[++c], 0, &parse_error);
+    } else if (!strcmp(argv[c], "-sharp_yuv")) {
+      config.use_sharp_yuv = 1;
     } else if (!strcmp(argv[c], "-pass") && c < argc - 1) {
       config.pass = ExUtilGetInt(argv[++c], 0, &parse_error);
     } else if (!strcmp(argv[c], "-pre") && c < argc - 1) {
@@ -945,7 +949,8 @@ int main(int argc, const char *argv[]) {
   // Read the input. We need to decide if we prefer ARGB or YUVA
   // samples, depending on the expected compression mode (this saves
   // some conversion steps).
-  picture.use_argb = (config.lossless || config.preprocessing > 0 ||
+  picture.use_argb = (config.lossless || config.use_sharp_yuv ||
+                      config.preprocessing > 0 ||
                       crop || (resize_w | resize_h) > 0);
   if (verbose) {
     StopwatchReset(&stop_watch);

man/cwebp.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH CWEBP 1 "September 02, 2016"
+.TH CWEBP 1 "January 20, 2017"
 .SH NAME
 cwebp \- compress an image file to a WebP file
 .SH SYNOPSIS
@@ -166,6 +166,10 @@ Use strong filtering (if filtering is being used thanks to the
 Disable strong filtering (if filtering is being used thanks to the
 \fB\-f\fP option) and use simple filtering instead.
 .TP
+.B \-sharp_yuv
+Use more accurate and sharper RGB->YUV conversion if needed. Note that this
+process is slower than the default 'fast' RGB->YUV conversion.
+.TP
 .BI \-sns " int
 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

src/enc/config_enc.c

@@ -54,6 +54,7 @@ int WebPConfigInitInternal(WebPConfig* config,
   config->low_memory = 0;
   config->near_lossless = 100;
   config->use_delta_palette = 0;
+  config->use_sharp_yuv = 0;
 
   // TODO(skal): tune.
   switch (preset) {
@@ -122,6 +123,8 @@ int WebPValidateConfig(const WebPConfig* config) {
   if (config->use_delta_palette < 0 || config->use_delta_palette > 1) {
     return 0;
   }
+  if (config->use_sharp_yuv < 0 || config->use_sharp_yuv > 1) return 0;
+
   return 1;
 }
 

src/enc/webp_enc.c

@@ -342,7 +342,7 @@ int WebPEncode(const WebPConfig* config, WebPPicture* pic) {
 
     if (pic->use_argb || pic->y == NULL || pic->u == NULL || pic->v == NULL) {
       // Make sure we have YUVA samples.
-      if (config->preprocessing & 4) {
+      if (config->use_sharp_yuv || (config->preprocessing & 4)) {
         if (!WebPPictureSharpARGBToYUVA(pic)) {
           return 0;
         }

src/webp/encode.h

@@ -20,7 +20,7 @@
 extern "C" {
 #endif
 
-#define WEBP_ENCODER_ABI_VERSION 0x020d    // MAJOR(8b) + MINOR(8b)
+#define WEBP_ENCODER_ABI_VERSION 0x020e    // MAJOR(8b) + MINOR(8b)
 
 // Note: forward declaring enumerations is not allowed in (strict) C and C++,
 // the types are left here for reference.
@@ -142,7 +142,9 @@ struct WebPConfig {
                           // value is 0.
 
   int use_delta_palette;  // reserved for future lossless feature
-  uint32_t pad[3];        // padding for later use
+  int use_sharp_yuv;      // if needed, use sharp (and slow) RGB->YUV conversion
+
+  uint32_t pad[2];        // padding for later use
 };
 
 // Enumerate some predefined settings for WebPConfig, depending on the type