Do not release user-provided buffer, if decoder failed.

modules/imgcodecs/include/opencv2/imgcodecs.hpp

@@ -322,7 +322,8 @@ CV_EXPORTS_W Mat imdecode( InputArray buf, int flags );
 @param buf Input array or vector of bytes.
 @param flags The same flags as in cv::imread, see cv::ImreadModes.
 @param dst The optional output placeholder for the decoded matrix. It can save the image
-reallocations when the function is called repeatedly for images of the same size.
+reallocations when the function is called repeatedly for images of the same size. In case of decoder
+failure the function returns empty cv::Mat object, but does not release user-provided dst buffer.
 */
 CV_EXPORTS Mat imdecode( InputArray buf, int flags, Mat* dst);
 

modules/imgcodecs/src/loadsave.cpp

@@ -800,7 +800,7 @@ imdecode_( const Mat& buf, int flags, Mat& mat )
 
     ImageDecoder decoder = findDecoder(buf_row);
     if( !decoder )
-        return 0;
+        return false;
 
     int scale_denom = 1;
     if( flags > IMREAD_LOAD_GDAL )
@@ -821,7 +821,7 @@ imdecode_( const Mat& buf, int flags, Mat& mat )
         filename = tempfile();
         FILE* f = fopen( filename.c_str(), "wb" );
         if( !f )
-            return 0;
+            return false;
         size_t bufSize = buf_row.total()*buf.elemSize();
         if (fwrite(buf_row.ptr(), 1, bufSize, f) != bufSize)
         {
@@ -859,7 +859,7 @@ imdecode_( const Mat& buf, int flags, Mat& mat )
                 CV_LOG_WARNING(NULL, "unable to remove temporary file:" << filename);
             }
         }
-        return 0;
+        return false;
     }
 
     // established the required input image size
@@ -905,7 +905,6 @@ imdecode_( const Mat& buf, int flags, Mat& mat )
 
     if (!success)
     {
-        mat.release();
         return false;
     }
 
@@ -929,7 +928,8 @@ Mat imdecode( InputArray _buf, int flags )
     CV_TRACE_FUNCTION();
 
     Mat buf = _buf.getMat(), img;
-    imdecode_( buf, flags, img );
+    if (!imdecode_(buf, flags, img))
+        img.release();
 
     return img;
 }
@@ -940,9 +940,10 @@ Mat imdecode( InputArray _buf, int flags, Mat* dst )
 
     Mat buf = _buf.getMat(), img;
     dst = dst ? dst : &img;
-    imdecode_( buf, flags, *dst );
-
-    return *dst;
+    if (imdecode_(buf, flags, *dst))
+        return *dst;
+    else
+        return cv::Mat();
 }
 
 static bool

modules/imgcodecs/test/test_grfmt.cpp

@@ -482,6 +482,19 @@ TEST(Imgcodecs, write_parameter_type)
     EXPECT_EQ(0, remove(tmp_file.c_str()));
 }
 
+TEST(Imgcodecs, imdecode_user_buffer)
+{
+    cv::Mat encoded = cv::Mat::zeros(1, 1024, CV_8UC1);
+    cv::Mat user_buffer(1, 1024, CV_8UC1);
+    cv::Mat result = cv::imdecode(encoded, IMREAD_ANYCOLOR, &user_buffer);
+    EXPECT_TRUE(result.empty());
+    // the function does not release user-provided buffer
+    EXPECT_FALSE(user_buffer.empty());
+
+    result = cv::imdecode(encoded, IMREAD_ANYCOLOR);
+    EXPECT_TRUE(result.empty());
+}
+
 }} // namespace
 
 #if defined(HAVE_OPENEXR) && defined(OPENCV_IMGCODECS_ENABLE_OPENEXR_TESTS)