Merge pull request opencv#24405 from kochanczyk:4.x

Extend the signature of imdecodemulti() opencv#24405

(Edited after addressing Reviewers' comments.)

Add an argument to `imdecodemulti()` to enable optional selection of pages of multi-page images.

Be default, all pages are decoded. If used, the additional argument may specify a continuous selection of pages to decode.


### Pull Request Readiness Checklist

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

- [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] I agree to contribute to the project under Apache 2 License.
- [X] The PR is proposed to the proper branch
- [ ] 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/imgcodecs/include/opencv2/imgcodecs.hpp

@@ -337,8 +337,9 @@ See cv::imreadmulti for the list of supported formats and flags description.
 @param buf Input array or vector of bytes.
 @param flags The same flags as in cv::imread, see cv::ImreadModes.
 @param mats A vector of Mat objects holding each page, if more than one.
+@param range A continuous selection of pages.
 */
-CV_EXPORTS_W bool imdecodemulti(InputArray buf, int flags, CV_OUT std::vector<Mat>& mats);
+CV_EXPORTS_W bool imdecodemulti(InputArray buf, int flags, CV_OUT std::vector<Mat>& mats, const cv::Range& range = Range::all());
 
 /** @brief Encodes an image into a memory buffer.
 

modules/imgcodecs/src/loadsave.cpp

@@ -1095,12 +1095,21 @@ imdecodemulti_(const Mat& buf, int flags, std::vector<Mat>& mats, int start, int
     return !mats.empty();
 }
 
-bool imdecodemulti(InputArray _buf, int flags, CV_OUT std::vector<Mat>& mats)
+bool imdecodemulti(InputArray _buf, int flags, CV_OUT std::vector<Mat>& mats, const Range& range)
 {
     CV_TRACE_FUNCTION();
 
     Mat buf = _buf.getMat();
-    return imdecodemulti_(buf, flags, mats, 0, -1);
+    if (range == Range::all())
+    {
+        return imdecodemulti_(buf, flags, mats, 0, -1);
+    }
+    else
+    {
+        CV_CheckGE(range.start, 0, "Range start cannot be negative.");
+        CV_CheckGT(range.size(), 0, "Range cannot be empty.");
+        return imdecodemulti_(buf, flags, mats, range.start, range.size());
+    }
 }
 
 bool imencode( const String& ext, InputArray _image,

modules/imgcodecs/test/test_tiff.cpp

@@ -965,7 +965,7 @@ TEST_P(Imgcodecs_Tiff_Modes, decode_multipage)
     }
 }
 
-TEST_P(Imgcodecs_Tiff_Modes, decode_multipage_use_memory_buffer)
+TEST_P(Imgcodecs_Tiff_Modes, decode_multipage_use_memory_buffer_all_pages)
 {
     const int mode = GetParam();
     const string root = cvtest::TS::ptr()->get_data_path();
@@ -984,13 +984,14 @@ TEST_P(Imgcodecs_Tiff_Modes, decode_multipage_use_memory_buffer)
     FILE* fp = fopen(filename.c_str(), "rb");
     ASSERT_TRUE(fp != NULL);
     fseek(fp, 0, SEEK_END);
-    long pos = ftell(fp);
-
-    std::vector<uchar> buf;
-    buf.resize((size_t)pos);
+    const size_t file_size = ftell(fp);
     fseek(fp, 0, SEEK_SET);
-    buf.resize(fread(&buf[0], 1, buf.size(), fp));
+
+    std::vector<uchar> buf(file_size);
+    const size_t actual_read = fread(&buf[0], 1, file_size, fp);
     fclose(fp);
+    ASSERT_EQ(file_size, actual_read);
+    ASSERT_EQ(file_size, static_cast<size_t>(buf.size()));
 
     bool res = imdecodemulti(buf, mode, pages);
     ASSERT_TRUE(res == true);
@@ -1002,6 +1003,60 @@ TEST_P(Imgcodecs_Tiff_Modes, decode_multipage_use_memory_buffer)
     }
 }
 
+TEST_P(Imgcodecs_Tiff_Modes, decode_multipage_use_memory_buffer_selected_pages)
+{
+    const int mode = GetParam();
+    const string root = cvtest::TS::ptr()->get_data_path();
+    const string filename = root + "readwrite/multipage.tif";
+    const string page_files[] = {
+        "readwrite/multipage_p1.tif",
+        "readwrite/multipage_p2.tif",
+        "readwrite/multipage_p3.tif",
+        "readwrite/multipage_p4.tif",
+        "readwrite/multipage_p5.tif",
+        "readwrite/multipage_p6.tif"
+    };
+    const size_t page_count = sizeof(page_files) / sizeof(page_files[0]);
+
+    FILE* fp = fopen(filename.c_str(), "rb");
+    ASSERT_TRUE(fp != NULL);
+    fseek(fp, 0, SEEK_END);
+    const size_t file_size = ftell(fp);
+    fseek(fp, 0, SEEK_SET);
+
+    std::vector<uchar> buf(file_size);
+    const size_t actual_read = fread(&buf[0], 1, file_size, fp);
+    fclose(fp);
+    ASSERT_EQ(file_size, actual_read);
+    ASSERT_EQ(file_size, static_cast<size_t>(buf.size()));
+
+    const Range range(1, page_count - 1);
+    ASSERT_GE(range.size(), 1);
+
+    vector<Mat> middle_pages_from_imread;
+    for (int page_i = range.start; page_i < range.end; page_i++)
+    {
+        const Mat page = imread(root + page_files[page_i], mode);
+        middle_pages_from_imread.push_back(page);
+    }
+    ASSERT_EQ(
+        static_cast<size_t>(range.size()),
+        static_cast<size_t>(middle_pages_from_imread.size())
+    );
+
+    vector<Mat> middle_pages_from_imdecodemulti;
+    const bool res = imdecodemulti(buf, mode, middle_pages_from_imdecodemulti, range);
+    ASSERT_TRUE(res == true);
+    EXPECT_EQ(middle_pages_from_imread.size(), middle_pages_from_imdecodemulti.size());
+
+    for (int i = 0, e = range.size(); i < e; i++)
+    {
+        EXPECT_PRED_FORMAT2(cvtest::MatComparator(0, 0),
+            middle_pages_from_imread[i],
+            middle_pages_from_imdecodemulti[i]);
+    }
+}
+
 const int all_modes[] =
 {
     IMREAD_UNCHANGED,