add getFrameCount()

modules/imgcodecs/include/opencv2/imgcodecs.hpp

@@ -305,11 +305,13 @@ The function imreadmulti loads a specified range from a multi-page image from th
 */
 CV_EXPORTS_W bool imreadmulti(const String& filename, CV_OUT std::vector<Mat>& mats, int start, int count, int flags = IMREAD_ANYCOLOR);
 
-/** @brief Returns the number of images inside the give file
+/** @brief Returns the number of images inside the given file
 
-The function imcount will return the number of pages in a multi-page image, or 1 for single-page images
+The function imcount returns the number of pages in a multi-page image (e.g. TIFF), the number of frames in an animation (e.g. AVIF), and 1 otherwise.
+If the image cannot be decoded, 0 is returned.
 @param filename Name of file to be loaded.
 @param flags Flag that can take values of cv::ImreadModes, default with cv::IMREAD_ANYCOLOR.
+@todo when cv::IMREAD_LOAD_GDAL flag used the return value will be 0 or 1 because OpenCV's GDAL decoder doesn't support multi-page reading yet.
 */
 CV_EXPORTS_W size_t imcount(const String& filename, int flags = IMREAD_ANYCOLOR);
 

modules/imgcodecs/src/grfmt_avif.cpp

@@ -195,6 +195,7 @@ bool AvifDecoder::readHeader() {
 
   m_width = decoder_->image->width;
   m_height = decoder_->image->height;
+  m_frame_count = decoder_->imageCount;
   channels_ = (decoder_->image->yuvFormat == AVIF_PIXEL_FORMAT_YUV400) ? 1 : 3;
   if (decoder_->alphaPresent) ++channels_;
   bit_depth_ = decoder_->image->depth;

modules/imgcodecs/src/grfmt_base.cpp

@@ -54,6 +54,7 @@ BaseImageDecoder::BaseImageDecoder()
     m_buf_supported = false;
     m_scale_denom = 1;
     m_use_rgb = false;
+    m_frame_count = 1;
 }
 
 

modules/imgcodecs/src/grfmt_base.hpp

@@ -64,6 +64,7 @@ public:
 
     int width() const { return m_width; }
     int height() const { return m_height; }
+    size_t getFrameCount() const { return m_frame_count; }
     virtual int type() const { return m_type; }
 
     ExifEntry_t getExifTag(const ExifTagName tag) const;
@@ -93,6 +94,7 @@ protected:
     bool m_buf_supported;
     bool m_use_rgb;       // flag of decode image as RGB order instead of BGR.
     ExifReader m_exif;
+    size_t  m_frame_count;
 };
 
 

modules/imgcodecs/src/grfmt_tiff.cpp

@@ -279,6 +279,7 @@ bool TiffDecoder::readHeader()
 
             m_width = wdth;
             m_height = hght;
+            m_frame_count = TIFFNumberOfDirectories(tif);
             if (ncn == 3 && photometric == PHOTOMETRIC_LOGLUV)
             {
                 m_type = CV_32FC3;

modules/imgcodecs/src/loadsave.cpp

@@ -1263,26 +1263,8 @@ void ImageCollection::Impl::init(String const& filename, int flags) {
     m_decoder->setSource(filename);
     CV_Assert(m_decoder->readHeader());
 
-    // count the pages of the image collection
-    size_t count = 1;
-    while(m_decoder->nextPage()) count++;
-
-    m_size = count;
+    m_size = m_decoder->getFrameCount();
     m_pages.resize(m_size);
-    // Reinitialize the decoder because we advanced to the last page while counting the pages of the image
-#ifdef HAVE_GDAL
-    if (m_flags != IMREAD_UNCHANGED && (m_flags & IMREAD_LOAD_GDAL) == IMREAD_LOAD_GDAL) {
-        m_decoder = GdalDecoder().newDecoder();
-    }
-    else {
-#endif
-    m_decoder = findDecoder(m_filename);
-#ifdef HAVE_GDAL
-    }
-#endif
-
-    m_decoder->setSource(m_filename);
-    m_decoder->readHeader();
 }
 
 size_t ImageCollection::Impl::size() const { return m_size; }

modules/imgcodecs/test/test_avif.cpp

@@ -296,6 +296,7 @@ TEST_P(Imgcodecs_Avif_Animation_WriteReadSuite, encode_decode) {
     return;
   }
   EXPECT_NO_THROW(cv::imwritemulti(output, anim_original, encoding_params_));
+  EXPECT_EQ(anim_original.size(), imcount(output));
 
   // Read from file.
   std::vector<cv::Mat> anim;