Merge pull request #27458 from xaos-cz:4.x

imread: GDAL multi-channel support #27458 

- tested on 30-channel FITS and 186-channel ENVI files

### 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
- [ ] There is a reference to the original bug report and related work
- [ ] 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/imgcodecs/src/grfmt_gdal.cpp

@@ -408,6 +408,9 @@ bool GdalDecoder::readData( Mat& img ){
         case GCI_AlphaBand:
             color = 3;
             break;
+        case GCI_Undefined:
+            color = c;
+            break;
         default:
             CV_Error(cv::Error::StsError, "Invalid/unsupported mode");
         }

modules/imgcodecs/test/test_gdal.cpp

@@ -0,0 +1,38 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html
+#include "test_precomp.hpp"
+#include "test_common.hpp"
+
+namespace opencv_test { namespace {
+
+#ifdef HAVE_GDAL
+
+static void test_gdal_read(const string filename) {
+    const string path = cvtest::findDataFile(filename);
+    Mat img;
+    ASSERT_NO_THROW(img = imread(path, cv::IMREAD_LOAD_GDAL | cv::IMREAD_ANYDEPTH | cv::IMREAD_ANYCOLOR));
+    ASSERT_FALSE(img.empty());
+    EXPECT_EQ(3, img.cols);
+    EXPECT_EQ(5, img.rows);
+    EXPECT_EQ(CV_MAKETYPE(CV_32F, 7), img.type());
+    EXPECT_EQ(101.125, (img.at<Vec<float, 7>>(0, 0)[0]));
+    EXPECT_EQ(203.500, (img.at<Vec<float, 7>>(2, 1)[3]));
+    EXPECT_EQ(305.875, (img.at<Vec<float, 7>>(4, 2)[6]));
+}
+
+TEST(Imgcodecs_gdal, read_envi)
+{
+    test_gdal_read("../cv/gdal/envi_test.raw");
+}
+
+
+TEST(Imgcodecs_gdal, read_fits)
+{
+    test_gdal_read("../cv/gdal/fits_test.fit");
+}
+
+
+#endif // HAVE_GDAL
+
+}} // namespace