Merge pull request #29691 from DPug888:fix-resize-area-channel-limit

allow cv::resize to support more than 4 channels in AREA path - #29691

Fixes  #29651

### 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.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/imgproc/src/resize.cpp

@@ -3848,7 +3848,7 @@ void resize(int src_type,
             }
 
             ResizeAreaFunc func = area_tab[depth];
-            CV_Assert( func != 0 && cn <= 4 );
+            CV_Assert( func != 0 );
 
             AutoBuffer<DecimateAlpha> _xytab((src_width + src_height)*2);
             DecimateAlpha* xtab = _xytab.data(), *ytab = xtab + src_width*2;

modules/imgproc/test/test_imgwarp.cpp

@@ -1275,6 +1275,45 @@ TEST(Imgproc_resize_area, regression)
     check_resize_area<ushort>(expected, actual, 1.0);
 }
 
+CV_ENUM(MultiChannelResizeInter, cv::INTER_LINEAR, cv::INTER_AREA);
+typedef testing::TestWithParam<testing::tuple<MultiChannelResizeInter, int>> Imgproc_ResizeMultiChannel;
+
+TEST_P(Imgproc_ResizeMultiChannel, smoke)
+{
+    int mode = get<0>(GetParam());
+    int cn = get<1>(GetParam());
+
+    cv::Mat src(64, 64, CV_8UC(cn));
+    cv::randu(src, 0, 255);
+
+    std::vector<cv::Mat> srcChannels;
+    cv::split(src, srcChannels);
+
+    cv::Size dsize = (mode == cv::INTER_LINEAR) ? cv::Size(32, 32) : cv::Size(31, 31);
+
+    cv::Mat dstMulti;
+    ASSERT_NO_THROW(cv::resize(src, dstMulti, dsize, 0, 0, mode));
+    EXPECT_EQ(dstMulti.channels(), cn);
+    EXPECT_EQ(dstMulti.size(), dsize);
+
+    std::vector<cv::Mat> dstChannels(cn);
+    for (int i = 0; i < cn; i++)
+        cv::resize(srcChannels[i], dstChannels[i], dsize, 0, 0, mode);
+
+    cv::Mat dstMerged;
+    cv::merge(dstChannels, dstMerged);
+
+    EXPECT_LE(cv::norm(dstMulti, dstMerged, cv::NORM_INF), 1)
+        << "Multi-channel resize (cn=" << cn << ", mode=" << mode
+        << ") does not match per-channel resize";
+}
+
+INSTANTIATE_TEST_CASE_P(/**/,
+    Imgproc_ResizeMultiChannel,
+        testing::Combine(
+            testing::Values(cv::INTER_LINEAR, cv::INTER_AREA),
+            testing::Values(5, 8)));
+
 TEST(Imgproc_resize_area, regression_half_round)
 {
     static uchar input_data[32 * 32];