Merge pull request #6335 from themightyoarfish:canny_kernel_sz_fix

modules/imgproc/src/canny.cpp

@@ -607,7 +607,7 @@ void cv::Canny( InputArray _src, OutputArray _dst,
     }
 
     if ((aperture_size & 1) == 0 || (aperture_size != -1 && (aperture_size < 3 || aperture_size > 7)))
-        CV_Error(CV_StsBadFlag, "Aperture size should be odd");
+        CV_Error(CV_StsBadFlag, "Aperture size should be odd between 3 and 7");
 
     if (low_thresh > high_thresh)
         std::swap(low_thresh, high_thresh);