provide better error messages

modules/imgproc/include/opencv2/imgproc.hpp

@@ -3157,10 +3157,12 @@ same object.
 
 @param signature1 First signature, a \f$\texttt{size1}\times \texttt{dims}+1\f$ floating-point matrix.
 Each row stores the point weight followed by the point coordinates. The matrix is allowed to have
-a single column (weights only) if the user-defined cost matrix is used.
+a single column (weights only) if the user-defined cost matrix is used. The weights must be
+non-negative and have at least one non-zero value.
 @param signature2 Second signature of the same format as signature1 , though the number of rows
 may be different. The total weights may be different. In this case an extra "dummy" point is added
-to either signature1 or signature2 .
+to either signature1 or signature2. The weights must be non-negative and have at least one non-zero
+value.
 @param distType Used metric. See cv::DistanceTypes.
 @param cost User-defined \f$\texttt{size1}\times \texttt{size2}\f$ cost matrix. Also, if a cost matrix
 is used, lower boundary lowerBound cannot be calculated because it needs a metric function.

modules/imgproc/src/emd.cpp

@@ -387,7 +387,7 @@ static int icvInitEMD( const float* signature1, int size1,
 
         }
         else if( weight < 0 )
-            CV_Error(CV_StsOutOfRange, "");
+            CV_Error(CV_StsBadArg, "signature1 must not contain negative weights");
     }
 
     for( i = 0; i < size2; i++ )
@@ -401,11 +401,13 @@ static int icvInitEMD( const float* signature1, int size1,
             state->idx2[dsize++] = i;
         }
         else if( weight < 0 )
-            CV_Error(CV_StsOutOfRange, "");
+            CV_Error(CV_StsBadArg, "signature2 must not contain negative weights");
     }
 
-    if( ssize == 0 || dsize == 0 )
-        CV_Error(CV_StsOutOfRange, "");
+    if( ssize == 0 )
+        CV_Error(CV_StsBadArg, "signature1 must contain at least one non-zero value");
+    if( dsize == 0 )
+        CV_Error(CV_StsBadArg, "signature2 must contain at least one non-zero value");
 
     /* if supply different than the demand, add a zero-cost dummy cluster */
     diff = s_sum - d_sum;