Fixed reading PNG iCCP compression method

Tests/test_file_png.py

@@ -619,6 +619,10 @@ def test_textual_chunks_after_idat(self) -> None:
         with Image.open("Tests/images/hopper_idat_after_image_end.png") as im:
             assert im.text == {"TXT": "VALUE", "ZIP": "VALUE"}
 
+    def test_unknown_compression_method(self) -> None:
+        with pytest.raises(SyntaxError, match="Unknown compression method"):
+            PngImagePlugin.PngImageFile("Tests/images/unknown_compression_method.png")
+
     def test_padded_idat(self) -> None:
         # This image has been manually hexedited
         # so that the IDAT chunk has padding at the end

src/PIL/PngImagePlugin.py

@@ -392,8 +392,8 @@ def chunk_iCCP(self, pos, length):
         # Compressed profile    n bytes (zlib with deflate compression)
         i = s.find(b"\0")
         logger.debug("iCCP profile name %r", s[:i])
-        logger.debug("Compression method %s", s[i])
-        comp_method = s[i]
+        comp_method = s[i + 1]
+        logger.debug("Compression method %s", comp_method)
         if comp_method != 0:
             msg = f"Unknown compression method {comp_method} in iCCP chunk"
             raise SyntaxError(msg)