Merge pull request #29742 from varun-jaiswal17:test_cleanup

ptcloud , photo test suit cleanup - #29742

## Test suite cleanup

### Given real assertions
- **ptcloud** — `HugeSceneGrowthTest`: zero assertions, including a `// Reset check` comment followed by no check.
- **ptcloud** — `PointCloud.SaveBadExtension`: passed an empty vertex set, so it exited at the empty-input guard and never reached the extension code it is named for.
- **ptcloud** — new `PointCloud.SaveEmptyVertices`: covers the early-return branch the above was hitting by accident.


### Moved
- **photo** — `Photo_Denoising.speed` → `perf/perf_denoising.cpp`: a `getTickCount` + `printf` stopwatch in the accuracy suite, asserting nothing, costing 393 ms per run.

### Library fixes found while doing the above
- **ptcloud** — `findPlanes` now converts 3-channel input instead of reshaping it: `Mat_<Vec4f>::operator=` reshapes when depths match, so a 320×240 `CV_32FC3` input silently became 240×240.
- **ptcloud** — new `RGBD_Plane.regression_3channel_matches_4channel`: nothing covered the documented 3-channel path, since all 40 `RgbdPlaneGenerate` cases feed `CV_32FC4`.


### 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/ptcloud/test/test_normal.cpp

@@ -722,4 +722,36 @@ TEST(RGBD_Plane, regression2309ValgrindCheck)
     findPlanes(points, noArray(), mask, planes, blockSize);
 }
 
+TEST(RGBD_Plane, regression_3channel_matches_4channel)
+{
+    const int rows = 240, cols = 320;
+
+    Mat points3(rows, cols, CV_32FC3);
+    Mat points4(rows, cols, CV_32FC4);
+    for (int v = 0; v < rows; v++)
+    {
+        for (int u = 0; u < cols; u++)
+        {
+            const float z = 2.f + 0.001f * u + 0.002f * v;
+            const Vec3f p((float)u * 0.01f, (float)v * 0.01f, z);
+            points3.at<Vec3f>(v, u) = p;
+            points4.at<Vec4f>(v, u) = Vec4f(p[0], p[1], p[2], 0.f);
+        }
+    }
+
+    Mat mask3, mask4;
+    std::vector<Vec4f> planes3, planes4;
+    findPlanes(points3, noArray(), mask3, planes3);
+    findPlanes(points4, noArray(), mask4, planes4);
+
+    EXPECT_EQ(points3.size(), mask3.size());
+    EXPECT_EQ(CV_8U, mask3.type());
+
+    ASSERT_EQ(mask4.size(), mask3.size());
+    EXPECT_EQ(0, cv::countNonZero(mask3 != mask4));
+    ASSERT_EQ(planes4.size(), planes3.size());
+    for (size_t i = 0; i < planes3.size(); i++)
+        EXPECT_LE(cv::norm(planes3[i], planes4[i], NORM_INF), 1e-6) << "plane " << i;
+}
+
 }} // namespace