Merge pull request #4512 from hugovk/fix-png-seek

Fix PNG seek

Author: hugovk

Tests/test_file_png.py

@@ -629,6 +629,14 @@ def test_exif_argument(self, tmp_path):
         with Image.open(test_file) as reloaded:
             assert reloaded.info["exif"] == b"Exif\x00\x00exifstring"
 
+    def test_tell(self, tmp_path):
+        with Image.open(TEST_PNG_FILE) as im:
+            assert im.tell() == 0
+
+    def test_seek(self, tmp_path):
+        with Image.open(TEST_PNG_FILE) as im:
+            im.seek(0)
+
 
 @pytest.mark.skipif(is_win32(), reason="Requires Unix or macOS")
 @skip_unless_feature("zlib")

src/PIL/PngImagePlugin.py

@@ -636,6 +636,7 @@ def _open(self):
         if self.fp.read(8) != _MAGIC:
             raise SyntaxError("not a PNG file")
         self.__fp = self.fp
+        self.__frame = 0
 
         #
         # Parse headers up to the first IDAT or fDAT chunk