Merge pull request #25981 from Kumataro:fix25971

imgproc: add specific error code when cvtColor is used on an image with an invalid number of channels #25981

close #25971

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/core/include/opencv2/core/check.hpp

@@ -135,6 +135,9 @@ CV_EXPORTS void CV_NORETURN check_failed_MatChannels(const int v, const CheckCon
 /// Example: depth == CV_32F || depth == CV_64F
 #define CV_CheckDepth(t, test_expr, msg)  CV__CHECK_CUSTOM_TEST(_, MatDepth, t, (test_expr), #t, #test_expr, msg)
 
+/// Example: channel == 1 || channel == 3
+#define CV_CheckChannels(t, test_expr, msg)  CV__CHECK_CUSTOM_TEST(_, MatChannels, t, (test_expr), #t, #test_expr, msg)
+
 /// Example: v == A || v == B
 #define CV_Check(v, test_expr, msg)  CV__CHECK_CUSTOM_TEST(_, auto, v, (test_expr), #v, #test_expr, msg)
 

modules/core/src/check.cpp

@@ -155,7 +155,12 @@ void check_failed_MatType(const int v, const CheckContext& ctx)
 }
 void check_failed_MatChannels(const int v, const CheckContext& ctx)
 {
-    check_failed_auto_<int>(v, ctx);
+    std::stringstream ss;
+    ss  << ctx.message << ":" << std::endl
+        << "    '" << ctx.p2_str << "'" << std::endl
+        << "where" << std::endl
+        << "    '" << ctx.p1_str << "' is " << v;
+    cv::error(cv::Error::BadNumChannels, ss.str(), ctx.func, ctx.file, ctx.line);
 }
 void check_failed_true(const bool v, const CheckContext& ctx)
 {

modules/imgproc/src/color.hpp

@@ -202,8 +202,8 @@ struct CvtHelper
         int stype = _src.type();
         scn = CV_MAT_CN(stype), depth = CV_MAT_DEPTH(stype);
 
-        CV_Check(scn, VScn::contains(scn), "Invalid number of channels in input image");
+        CV_CheckChannels(scn, VScn::contains(scn), "Invalid number of channels in input image");
-        CV_Check(dcn, VDcn::contains(dcn), "Invalid number of channels in output image");
+        CV_CheckChannels(dcn, VDcn::contains(dcn), "Invalid number of channels in output image");
         CV_CheckDepth(depth, VDepth::contains(depth), "Unsupported depth of input image");
 
         if (_src.getObj() == _dst.getObj()) // inplace processing (#6653)
@@ -247,8 +247,8 @@ struct OclHelper
         int scn = src.channels();
         int depth = src.depth();
 
-        CV_Check(scn, VScn::contains(scn), "Invalid number of channels in input image");
+        CV_CheckChannels(scn, VScn::contains(scn), "Invalid number of channels in input image");
-        CV_Check(dcn, VDcn::contains(dcn), "Invalid number of channels in output image");
+        CV_CheckChannels(dcn, VDcn::contains(dcn), "Invalid number of channels in output image");
         CV_CheckDepth(depth, VDepth::contains(depth), "Unsupported depth of input image");
 
         switch (sizePolicy)

modules/imgproc/src/color.simd_helpers.hpp

@@ -89,8 +89,8 @@ struct CvtHelper
         int stype = _src.type();
         scn = CV_MAT_CN(stype), depth = CV_MAT_DEPTH(stype);
 
-        CV_Check(scn, VScn::contains(scn), "Invalid number of channels in input image");
+        CV_CheckChannels(scn, VScn::contains(scn), "Invalid number of channels in input image");
-        CV_Check(dcn, VDcn::contains(dcn), "Invalid number of channels in output image");
+        CV_CheckChannels(dcn, VDcn::contains(dcn), "Invalid number of channels in output image");
         CV_CheckDepth(depth, VDepth::contains(depth), "Unsupported depth of input image");
 
         if (_src.getObj() == _dst.getObj()) // inplace processing (#6653)

modules/imgproc/test/test_color.cpp

@@ -3203,4 +3203,20 @@ TEST(ImgProc_RGB2Lab, NaN_21111)
 #endif
 }
 
+// See https://github.com/opencv/opencv/issues/25971
+// If num of channels is not suitable for selected cv::ColorConversionCodes,
+// e.code must be cv::Error::BadNumChannels.
+TEST(ImgProc_cvtColor_InvalidNumOfChannels, regression_25971)
+{
+    try {
+        cv::Mat src = cv::Mat::zeros(100, 100, CV_8UC1);
+        cv::Mat dst;
+        EXPECT_THROW(cv::cvtColor(src, dst, COLOR_RGB2GRAY), cv::Exception);
+    }catch(const cv::Exception& e) {
+        EXPECT_EQ(e.code, cv::Error::BadNumChannels);
+    }catch(...) {
+        FAIL() << "Unexpected exception is happened.";
+    }
+}
+
 }} // namespace