gif2webp: Add '-min-size' option to get best compression.

This disables key-frame insertion and tries both dispose methods for
each frame.

Change-Id: Ib167747198fd1d98cb93321f76826e91228f24d8

examples/gif2webp.c

@@ -231,6 +231,10 @@ static void Help(void) {
          "                           or lossless compression heuristically\n");
   printf("  -q <float> ............. quality factor (0:small..100:big)\n");
   printf("  -m <int> ............... compression method (0=fast, 6=slowest)\n");
+  printf("  -min_size .............. minimize output size (default:off)\n"
+         "                           lossless compression by default; can be\n"
+         "                           combined with -q, -m, -lossy or -mixed\n"
+         "                           options\n");
   printf("  -kmin <int> ............ min distance between key frames\n");
   printf("  -kmax <int> ............ max distance between key frames\n");
   printf("  -f <int> ............... filter strength (0=off..100)\n");
@@ -274,6 +278,7 @@ int main(int argc, const char *argv[]) {
   int stored_icc = 0;  // Whether we have already stored an ICC profile.
   int stored_xmp = 0;
 
+  int minimize_size = 0;
   int default_kmin = 1;  // Whether to use default kmin value.
   int default_kmax = 1;
   size_t kmin = 0;
@@ -307,6 +312,8 @@ int main(int argc, const char *argv[]) {
       config.quality = ExUtilGetFloat(argv[++c], &parse_error);
     } else if (!strcmp(argv[c], "-m") && c < argc - 1) {
       config.method = ExUtilGetInt(argv[++c], 0, &parse_error);
+    } else if (!strcmp(argv[c], "-min_size")) {
+      minimize_size = 1;
     } else if (!strcmp(argv[c], "-kmax") && c < argc - 1) {
       kmax = ExUtilGetUInt(argv[++c], 0, &parse_error);
       default_kmax = 0;
@@ -466,7 +473,7 @@ int main(int argc, const char *argv[]) {
           WebPUtilClearPic(&frame, NULL);
 
           // Initialize cache.
-          cache = WebPFrameCacheNew(frame.width, frame.height,
+          cache = WebPFrameCacheNew(frame.width, frame.height, minimize_size,
                                     kmin, kmax, allow_mixed);
           if (cache == NULL) goto End;
 

examples/gif2webp_util.c

@@ -287,6 +287,9 @@ struct WebPFrameCache {
                              // transparent pixels in a frame.
   int keyframe;              // Index of selected keyframe relative to 'start'.
 
+  // TODO(urvang): Create a struct WebPAnimationEncodingConfig for these
+  // encoding parameters.
+  int min_size;                  // If true, produce the smallest output.
   size_t kmin;                   // Min distance between key frames.
   size_t kmax;                   // Max distance between key frames.
   size_t count_since_key_frame;  // Frames seen since the last key frame.
@@ -319,7 +322,7 @@ static void CacheReset(WebPFrameCache* const cache) {
   cache->keyframe = KEYFRAME_NONE;
 }
 
-WebPFrameCache* WebPFrameCacheNew(int width, int height,
+WebPFrameCache* WebPFrameCacheNew(int width, int height, int minimize_size,
                                   size_t kmin, size_t kmax, int allow_mixed) {
   WebPFrameCache* cache = (WebPFrameCache*)WebPSafeCalloc(1, sizeof(*cache));
   if (cache == NULL) return NULL;
@@ -354,7 +357,12 @@ WebPFrameCache* WebPFrameCacheNew(int width, int height,
   WebPUtilClearPic(&cache->prev_to_prev_canvas_disposed, NULL);
 
   // Cache data.
+  cache->min_size = minimize_size;
   cache->allow_mixed = allow_mixed;
+  if (cache->min_size) {  // Disable keyframe insertion.
+    kmax = ~0;
+    kmin = kmax - 1;
+  }
   cache->kmin = kmin;
   cache->kmax = kmax;
   cache->count_since_key_frame = 0;
@@ -790,7 +798,10 @@ static WebPEncodingError SetFrame(WebPFrameCache* const cache,
     GetSubRect(prev_canvas_disposed, curr_canvas, orig_rect, is_key_frame,
                &rect_bg, &sub_frame_bg);
 
-    if (RectArea(&rect_bg) < RectArea(&rect_none)) {
+    if (cache->min_size) {  // Try both dispose methods.
+      try_dispose_bg = 1;
+      try_dispose_none = 1;
+    } else if (RectArea(&rect_bg) < RectArea(&rect_none)) {
       try_dispose_bg = 1;  // Pick DISPOSE_BACKGROUND.
       try_dispose_none = 0;
     }

examples/gif2webp_util.h

@@ -51,10 +51,12 @@ typedef struct WebPFrameCache WebPFrameCache;
 
 // Given the minimum distance between key frames 'kmin' and maximum distance
 // between key frames 'kmax', returns an appropriately allocated cache object.
+// If 'minimize_size' is true, optimizes for file size. This also implies that
+// keyframe addition is off.
 // If 'allow_mixed' is true, the subsequent calls to WebPFrameCacheAddFrame()
 // will heuristically pick lossy or lossless compression for each frame.
 // Use WebPFrameCacheDelete() to deallocate the 'cache'.
-WebPFrameCache* WebPFrameCacheNew(int width, int height,
+WebPFrameCache* WebPFrameCacheNew(int width, int height, int minimize_size,
                                   size_t kmin, size_t kmax, int allow_mixed);
 
 // Release all the frame data from 'cache' and free 'cache'.

man/gif2webp.1

@@ -54,6 +54,12 @@ additional encoding possibilities and decide on the quality gain.
 Lower value can result is faster processing time at the expense of
 larger file size and lower compression quality.
 .TP
+.BI \-min_size
+Encode image to achieve smallest size. This disables key frame insertion and
+picks the dispose method resulting in smallest output for each frame. It uses
+lossless compression by default, but can be combined with \-q, \-m, \-lossy or
+\-mixed options.
+.TP
 .BI \-kmin " int
 .TP
 .BI \-kmax " int