added compression strategy as a parameter (another request from ticket #1452)

modules/highgui/include/opencv2/highgui/highgui.hpp

@@ -150,6 +150,12 @@ enum
 {
     IMWRITE_JPEG_QUALITY =1,
     IMWRITE_PNG_COMPRESSION =16,
+    IMWRITE_PNG_STRATEGY =17,
+    IMWRITE_PNG_STRATEGY_DEFAULT =0,
+    IMWRITE_PNG_STRATEGY_FILTERED =1,
+    IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY =2,
+    IMWRITE_PNG_STRATEGY_RLE =3,
+    IMWRITE_PNG_STRATEGY_FIXED =4,
     IMWRITE_PXM_BINARY =32
 };
     

modules/highgui/include/opencv2/highgui/highgui_c.h

@@ -217,6 +217,12 @@ enum
 {
     CV_IMWRITE_JPEG_QUALITY =1,
     CV_IMWRITE_PNG_COMPRESSION =16,
+    CV_IMWRITE_PNG_STRATEGY =17,
+    CV_IMWRITE_PNG_STRATEGY_DEFAULT =0,
+    CV_IMWRITE_PNG_STRATEGY_FILTERED =1,
+    CV_IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY =2,
+    CV_IMWRITE_PNG_STRATEGY_RLE =3,
+    CV_IMWRITE_PNG_STRATEGY_FIXED =4,
     CV_IMWRITE_PXM_BINARY =32
 };
 

modules/highgui/src/grfmt_png.cpp

@@ -312,6 +312,7 @@ void PngEncoder::flushBuf(void*)
 bool  PngEncoder::write( const Mat& img, const vector<int>& params )
 {
     int compression_level = 0;
+    int compression_strategy = Z_RLE;
 
     for( size_t i = 0; i < params.size(); i += 2 )
     {
@@ -320,6 +321,11 @@ bool  PngEncoder::write( const Mat& img, const vector<int>& params )
             compression_level = params[i+1];
             compression_level = MIN(MAX(compression_level, 0), MAX_MEM_LEVEL);
         }
+        if( params[i] == CV_IMWRITE_PNG_STRATEGY )
+        {
+            compression_strategy = params[i+1];
+            compression_strategy = MIN(MAX(compression_strategy, 0), Z_FIXED); 
+        }
     }
 
     png_structp png_ptr = png_create_write_struct( PNG_LIBPNG_VER_STRING, 0, 0, 0 );
@@ -366,7 +372,7 @@ bool  PngEncoder::write( const Mat& img, const vector<int>& params )
                         png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_FILTER_SUB);
                         png_set_compression_level(png_ptr, Z_BEST_SPEED);
                     }
-                    png_set_compression_strategy(png_ptr, Z_FILTERED);
+                    png_set_compression_strategy(png_ptr, compression_strategy);
 
                     png_set_IHDR( png_ptr, info_ptr, width, height, depth == CV_8U ? 8 : 16,
                         channels == 1 ? PNG_COLOR_TYPE_GRAY :