#2992: update after review

modules/imgcodecs/include/opencv2/imgcodecs.hpp

@@ -56,17 +56,17 @@ enum { IMREAD_UNCHANGED  = -1, // 8bit, color or not
        IMREAD_ANYCOLOR   = 4   // ?, any color
      };
 
-enum { IMWRITE_JPEG_QUALITY       = 1,
-       IMWRITE_JPEG_PROGRESSIVE   = 2,
-       IMWRITE_JPEG_OPTIMIZE      = 3,
-       IMWRITE_JPEG_RST_INTERVAL  = 4,
-       IMWRITE_JPEG_LUM_QUALITY   = 5,
-       IMWRITE_JPEG_CHROM_QUALITY = 6,
-       IMWRITE_PNG_COMPRESSION    = 16,
-       IMWRITE_PNG_STRATEGY       = 17,
-       IMWRITE_PNG_BILEVEL        = 18,
-       IMWRITE_PXM_BINARY         = 32,
-       IMWRITE_WEBP_QUALITY       = 64
+enum { IMWRITE_JPEG_QUALITY        = 1,
+       IMWRITE_JPEG_PROGRESSIVE    = 2,
+       IMWRITE_JPEG_OPTIMIZE       = 3,
+       IMWRITE_JPEG_RST_INTERVAL   = 4,
+       IMWRITE_JPEG_LUMA_QUALITY   = 5,
+       IMWRITE_JPEG_CHROMA_QUALITY = 6,
+       IMWRITE_PNG_COMPRESSION     = 16,
+       IMWRITE_PNG_STRATEGY        = 17,
+       IMWRITE_PNG_BILEVEL         = 18,
+       IMWRITE_PXM_BINARY          = 32,
+       IMWRITE_WEBP_QUALITY        = 64
      };
 
 enum { IMWRITE_PNG_STRATEGY_DEFAULT      = 0,

modules/imgcodecs/include/opencv2/imgcodecs/imgcodecs_c.h

@@ -77,8 +77,8 @@ enum
     CV_IMWRITE_JPEG_PROGRESSIVE =2,
     CV_IMWRITE_JPEG_OPTIMIZE =3,
     CV_IMWRITE_JPEG_RST_INTERVAL =4,
-    CV_IMWRITE_JPEG_LUM_QUALITY =5,
-    CV_IMWRITE_JPEG_CHROM_QUALITY =6,
+    CV_IMWRITE_JPEG_LUMA_QUALITY =5,
+    CV_IMWRITE_JPEG_CHROMA_QUALITY =6,
     CV_IMWRITE_PNG_COMPRESSION =16,
     CV_IMWRITE_PNG_STRATEGY =17,
     CV_IMWRITE_PNG_BILEVEL =18,

modules/imgcodecs/src/grfmt_jpeg.cpp

@@ -601,8 +601,8 @@ bool JpegEncoder::write( const Mat& img, const std::vector<int>& params )
         int progressive = 0;
         int optimize = 0;
         int rst_interval = 0;
-        int lum_quality = 100;
-        int chrom_quality = 100;
+        int luma_quality = -1;
+        int chroma_quality = -1;
 
         for( size_t i = 0; i < params.size(); i += 2 )
         {
@@ -622,16 +622,27 @@ bool JpegEncoder::write( const Mat& img, const std::vector<int>& params )
                 optimize = params[i+1];
             }
 
-            if( params[i] == CV_IMWRITE_JPEG_LUM_QUALITY )
+            if( params[i] == CV_IMWRITE_JPEG_LUMA_QUALITY )
             {
-                lum_quality = params[i+1];
-                lum_quality = MIN(MAX(lum_quality, 0), 100);
+                if (params[i+1] >= 0)
+                {
+                    luma_quality = MIN(MAX(params[i+1], 0), 100);
+
+                    quality = luma_quality;
+
+                    if (chroma_quality < 0)
+                    {
+                        chroma_quality = luma_quality;
+                    }
+                }
             }
 
-            if( params[i] == CV_IMWRITE_JPEG_CHROM_QUALITY )
+            if( params[i] == CV_IMWRITE_JPEG_CHROMA_QUALITY )
             {
-                chrom_quality = params[i+1];
-                chrom_quality = MIN(MAX(chrom_quality, 0), 100);
+                if (params[i+1] >= 0)
+                {
+                    chroma_quality = MIN(MAX(params[i+1], 0), 100);
+                }
             }
 
             if( params[i] == CV_IMWRITE_JPEG_RST_INTERVAL )
@@ -643,6 +654,7 @@ bool JpegEncoder::write( const Mat& img, const std::vector<int>& params )
 
         jpeg_set_defaults( &cinfo );
         cinfo.restart_interval = rst_interval;
+
         jpeg_set_quality( &cinfo, quality,
                           TRUE /* limit to baseline-JPEG values */ );
         if( progressive )
@@ -651,17 +663,20 @@ bool JpegEncoder::write( const Mat& img, const std::vector<int>& params )
             cinfo.optimize_coding = TRUE;
 
 #if JPEG_LIB_VERSION >= 70
-        cinfo.q_scale_factor[0] = jpeg_quality_scaling(lum_quality);
-        cinfo.q_scale_factor[1] = jpeg_quality_scaling(chrom_quality);
-        if ( lum_quality != chrom_quality )
+        if (luma_quality >= 0 && chroma_quality >= 0)
         {
-            /* disable subsampling - ref. Libjpeg.txt */
-            cinfo.comp_info[0].v_samp_factor = 1;
-            cinfo.comp_info[0].h_samp_factor = 1;
-            cinfo.comp_info[1].v_samp_factor = 1;
-            cinfo.comp_info[1].h_samp_factor = 1;
+            cinfo.q_scale_factor[0] = jpeg_quality_scaling(luma_quality);
+            cinfo.q_scale_factor[1] = jpeg_quality_scaling(chroma_quality);
+            if ( luma_quality != chroma_quality )
+            {
+                /* disable subsampling - ref. Libjpeg.txt */
+                cinfo.comp_info[0].v_samp_factor = 1;
+                cinfo.comp_info[0].h_samp_factor = 1;
+                cinfo.comp_info[1].v_samp_factor = 1;
+                cinfo.comp_info[1].h_samp_factor = 1;
+            }
+            jpeg_default_qtables( &cinfo, TRUE );
         }
-        jpeg_default_qtables( &cinfo, TRUE );
 #endif // #if JPEG_LIB_VERSION >= 70
 
         jpeg_start_compress( &cinfo, TRUE );