Add APNG test cases

Includes tests for reading and writing APNG files.

The tests for reading files are based on the APNG browser compatibility
tests from https://philip.html5.org/tests/apng/tests.html
(which is linked in the Tests section of https://wiki.mozilla.org/APNG_Specification)

Tests/test_file_png.py

@@ -3,7 +3,7 @@ import zlib
 from io import BytesIO
 
 import pytest
-from PIL import Image, ImageFile, PngImagePlugin
+from PIL import Image, ImageFile, ImageSequence, PngImagePlugin
 
 from .helper import (
     PillowLeakTestCase,
@@ -18,6 +18,7 @@ from .helper import (
     skip_unless_feature,
 )
 
+
 # sample png stream
 
 TEST_PNG_FILE = "Tests/images/hopper.png"
@@ -624,16 +625,521 @@ class TestFilePng(PillowTestCase):
         with Image.open(test_file) as reloaded:
             assert reloaded.info["exif"] == b"Exif\x00\x00exifstring"
 
-    @skip_unless_feature("webp")
-    @skip_unless_feature("webp_anim")
-    def test_apng(self):
-        with Image.open("Tests/images/iss634.apng") as im:
-            assert im.get_format_mimetype() == "image/apng"
+    # APNG browser support tests and fixtures via:
+    # https://philip.html5.org/tests/apng/tests.html
+    # (referenced from https://wiki.mozilla.org/APNG_Specification)
+    def test_apng_basic(self):
+        im = Image.open("Tests/images/apng/single_frame.png")
+        self.assertTrue(im.is_animated)
+        self.assertEqual(im.get_format_mimetype(), "image/apng")
+        self.assertIsNone(im.info.get("default_image"))
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/single_frame_default.png")
+        self.assertTrue(im.is_animated)
+        self.assertEqual(im.get_format_mimetype(), "image/apng")
+        self.assertTrue(im.info.get("default_image"))
+        self.assertEqual(im.getpixel((0, 0)), (255, 0, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (255, 0, 0, 255))
+        im.seek(1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        # test out of bounds seek
+        with self.assertRaises(EOFError):
+            im.seek(2)
+
+        # test rewind support
+        im.seek(0)
+        self.assertEqual(im.getpixel((0, 0)), (255, 0, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (255, 0, 0, 255))
+        im.seek(1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_fdat(self):
+        im = Image.open("Tests/images/apng/split_fdat.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/split_fdat_zero_chunk.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_dispose(self):
+        im = Image.open("Tests/images/apng/dispose_op_none.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/dispose_op_background.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 0, 0))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+        im = Image.open("Tests/images/apng/dispose_op_background_final.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/dispose_op_previous.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/dispose_op_previous_final.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/dispose_op_previous_first.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 0, 0))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+    def test_apng_dispose_region(self):
+        im = Image.open("Tests/images/apng/dispose_op_none_region.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/dispose_op_background_before_region.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 0, 0))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+        im = Image.open("Tests/images/apng/dispose_op_background_region.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 255, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+        im = Image.open("Tests/images/apng/dispose_op_previous_region.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_blend(self):
+        im = Image.open("Tests/images/apng/blend_op_source_solid.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/blend_op_source_transparent.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 0, 0))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+        im = Image.open("Tests/images/apng/blend_op_source_near_transparent.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 2))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 2))
+
+        im = Image.open("Tests/images/apng/blend_op_over.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/blend_op_over_near_transparent.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 97))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_chunk_order(self):
+        im = Image.open("Tests/images/apng/fctl_actl.png")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_delay(self):
+        im = Image.open("Tests/images/apng/delay.png")
+        im.seek(1)
+        self.assertEqual(im.info.get("duration"), 500.0)
+        im.seek(2)
+        self.assertEqual(im.info.get("duration"), 1000.0)
+        im.seek(3)
+        self.assertEqual(im.info.get("duration"), 500.0)
+        im.seek(4)
+        self.assertEqual(im.info.get("duration"), 1000.0)
+
+        im = Image.open("Tests/images/apng/delay_round.png")
+        im.seek(1)
+        self.assertEqual(im.info.get("duration"), 500.0)
+        im.seek(2)
+        self.assertEqual(im.info.get("duration"), 1000.0)
+
+        im = Image.open("Tests/images/apng/delay_short_max.png")
+        im.seek(1)
+        self.assertEqual(im.info.get("duration"), 500.0)
+        im.seek(2)
+        self.assertEqual(im.info.get("duration"), 1000.0)
+
+        im = Image.open("Tests/images/apng/delay_zero_denom.png")
+        im.seek(1)
+        self.assertEqual(im.info.get("duration"), 500.0)
+        im.seek(2)
+        self.assertEqual(im.info.get("duration"), 1000.0)
+
+        im = Image.open("Tests/images/apng/delay_zero_numer.png")
+        im.seek(1)
+        self.assertEqual(im.info.get("duration"), 0.0)
+        im.seek(2)
+        self.assertEqual(im.info.get("duration"), 0.0)
+        im.seek(3)
+        self.assertEqual(im.info.get("duration"), 500.0)
+        im.seek(4)
+        self.assertEqual(im.info.get("duration"), 1000.0)
+
+    def test_apng_num_plays(self):
+        im = Image.open("Tests/images/apng/num_plays.png")
+        self.assertEqual(im.info.get("loop"), 0)
+
+        im = Image.open("Tests/images/apng/num_plays_1.png")
+        self.assertEqual(im.info.get("loop"), 1)
+
+    def test_apng_mode(self):
+        im = Image.open("Tests/images/apng/mode_16bit.png")
+        self.assertEqual(im.mode, "RGBA")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 128, 191))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 128, 191))
+
+        im = Image.open("Tests/images/apng/mode_greyscale.png")
+        self.assertEqual(im.mode, "L")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), 128)
+        self.assertEqual(im.getpixel((64, 32)), 255)
+
+        im = Image.open("Tests/images/apng/mode_greyscale_alpha.png")
+        self.assertEqual(im.mode, "LA")
+        im.seek(im.n_frames - 1)
+        self.assertEqual(im.getpixel((0, 0)), (128, 191))
+        self.assertEqual(im.getpixel((64, 32)), (128, 191))
+
+        im = Image.open("Tests/images/apng/mode_palette.png")
+        self.assertEqual(im.mode, "P")
+        im.seek(im.n_frames - 1)
+        im = im.convert("RGB")
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0))
+
+        im = Image.open("Tests/images/apng/mode_palette_alpha.png")
+        self.assertEqual(im.mode, "P")
+        im.seek(im.n_frames - 1)
+        im = im.convert("RGBA")
+        self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+        self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/mode_palette_1bit_alpha.png")
+        self.assertEqual(im.mode, "P")
+        im.seek(im.n_frames - 1)
+        im = im.convert("RGBA")
+        self.assertEqual(im.getpixel((0, 0)), (0, 0, 255, 128))
+        self.assertEqual(im.getpixel((64, 32)), (0, 0, 255, 128))
+
+    def test_apng_chunk_errors(self):
+        im = Image.open("Tests/images/apng/chunk_no_actl.png")
+        self.assertFalse(im.is_animated)
+
+        def open():
+            im = Image.open("Tests/images/apng/chunk_multi_actl.png")
+            im.load()
+
+        pytest.warns(UserWarning, open)
+        self.assertFalse(im.is_animated)
+
+        im = Image.open("Tests/images/apng/chunk_actl_after_idat.png")
+        self.assertFalse(im.is_animated)
+
+        im = Image.open("Tests/images/apng/chunk_no_fctl.png")
+        with self.assertRaises(SyntaxError):
+            im.seek(im.n_frames - 1)
+
+        im = Image.open("Tests/images/apng/chunk_repeat_fctl.png")
+        with self.assertRaises(SyntaxError):
+            im.seek(im.n_frames - 1)
+
+        im = Image.open("Tests/images/apng/chunk_no_fdat.png")
+        with self.assertRaises(SyntaxError):
+            im.seek(im.n_frames - 1)
+
+    def test_apng_syntax_errors(self):
+        def open():
+            im = Image.open("Tests/images/apng/syntax_num_frames_zero.png")
+            self.assertFalse(im.is_animated)
+            with self.assertRaises(OSError):
+                im.load()
+
+        pytest.warns(UserWarning, open)
+
+        def open():
+            im = Image.open("Tests/images/apng/syntax_num_frames_zero_default.png")
+            self.assertFalse(im.is_animated)
+            im.load()
+
+        pytest.warns(UserWarning, open)
+
+        # we can handle this case gracefully
+        exception = None
+        im = Image.open("Tests/images/apng/syntax_num_frames_low.png")
+        try:
+            im.seek(im.n_frames - 1)
+        except Exception as e:
+            exception = e
+        self.assertIsNone(exception)
+
+        with self.assertRaises(SyntaxError):
+            im = Image.open("Tests/images/apng/syntax_num_frames_high.png")
+            im.seek(im.n_frames - 1)
+            im.load()
+
+        def open():
+            im = Image.open("Tests/images/apng/syntax_num_frames_invalid.png")
+            self.assertFalse(im.is_animated)
+            im.load()
+
+        pytest.warns(UserWarning, open)
+
+    def test_apng_sequence_errors(self):
+        test_files = [
+            "sequence_start.png",
+            "sequence_gap.png",
+            "sequence_repeat.png",
+            "sequence_repeat_chunk.png",
+            "sequence_reorder.png",
+            "sequence_reorder_chunk.png",
+            "sequence_fdat_fctl.png",
+        ]
+        for f in test_files:
+            with self.assertRaises(SyntaxError):
+                im = Image.open("Tests/images/apng/{0}".format(f))
+                im.seek(im.n_frames - 1)
+                im.load()
+
+    def test_apng_save(self):
+        im = Image.open("Tests/images/apng/single_frame.png")
+        test_file = self.tempfile("temp.png")
+        im.save(test_file, save_all=True)
+
+        with Image.open(test_file) as im:
+            im.load()
+            self.assertTrue(im.is_animated)
+            self.assertEqual(im.get_format_mimetype(), "image/apng")
+            self.assertIsNone(im.info.get("default_image"))
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        im = Image.open("Tests/images/apng/single_frame_default.png")
+        frames = []
+        for im in ImageSequence.Iterator(im):
+            frames.append(im.copy())
+        frames[0].save(
+            test_file, save_all=True, default_image=True, append_images=frames[1:]
+        )
+
+        with Image.open(test_file) as im:
+            im.load()
+            self.assertTrue(im.is_animated)
+            self.assertEqual(im.get_format_mimetype(), "image/apng")
+            self.assertTrue(im.info.get("default_image"))
+            im.seek(1)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_save_duration_loop(self):
+        test_file = self.tempfile("temp.png")
+        im = Image.open("Tests/images/apng/delay.png")
+        frames = []
+        durations = []
+        loop = im.info.get("loop")
+        default_image = im.info.get("default_image")
+        for i, im in enumerate(ImageSequence.Iterator(im)):
+            frames.append(im.copy())
+            if i != 0 or not default_image:
+                durations.append(im.info.get("duration", 0))
+        frames[0].save(
+            test_file,
+            save_all=True,
+            default_image=default_image,
+            append_images=frames[1:],
+            duration=durations,
+            loop=loop,
+        )
+        with Image.open(test_file) as im:
+            im.load()
+            self.assertEqual(im.info.get("loop"), loop)
+            im.seek(1)
+            self.assertEqual(im.info.get("duration"), 500.0)
+            im.seek(2)
+            self.assertEqual(im.info.get("duration"), 1000.0)
+            im.seek(3)
+            self.assertEqual(im.info.get("duration"), 500.0)
+            im.seek(4)
+            self.assertEqual(im.info.get("duration"), 1000.0)
+
+        # test removal of duplicated frames
+        frame = Image.new("RGBA", (128, 64), (255, 0, 0, 255))
+        frame.save(test_file, save_all=True, append_images=[frame], duration=[500, 250])
+        with Image.open(test_file) as im:
+            im.load()
+            self.assertEqual(im.n_frames, 1)
+            self.assertEqual(im.info.get("duration"), 750)
 
             # This also tests reading unknown PNG chunks (fcTL and fdAT) in load_end
             with Image.open("Tests/images/iss634.webp") as expected:
                 assert_image_similar(im, expected, 0.23)
 
+    def test_apng_save_disposal(self):
+        test_file = self.tempfile("temp.png")
+        size = (128, 64)
+        red = Image.new("RGBA", size, (255, 0, 0, 255))
+        green = Image.new("RGBA", size, (0, 255, 0, 255))
+        transparent = Image.new("RGBA", size, (0, 0, 0, 0))
+
+        # test APNG_DISPOSE_OP_NONE
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[green, transparent],
+            disposal=PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            blend=PngImagePlugin.APNG_BLEND_OP_OVER,
+        )
+        with Image.open(test_file) as im:
+            im.seek(2)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        # test APNG_DISPOSE_OP_BACKGROUND
+        disposal = [
+            PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            PngImagePlugin.APNG_DISPOSE_OP_BACKGROUND,
+            PngImagePlugin.APNG_DISPOSE_OP_NONE,
+        ]
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[red, transparent],
+            disposal=disposal,
+            blend=PngImagePlugin.APNG_BLEND_OP_OVER,
+        )
+        with Image.open(test_file) as im:
+            im.seek(2)
+            self.assertEqual(im.getpixel((0, 0)), (0, 0, 0, 0))
+            self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+        disposal = [
+            PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            PngImagePlugin.APNG_DISPOSE_OP_BACKGROUND,
+        ]
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[green],
+            disposal=disposal,
+            blend=PngImagePlugin.APNG_BLEND_OP_OVER,
+        )
+        with Image.open(test_file) as im:
+            im.seek(1)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        # test APNG_DISPOSE_OP_PREVIOUS
+        disposal = [
+            PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            PngImagePlugin.APNG_DISPOSE_OP_PREVIOUS,
+            PngImagePlugin.APNG_DISPOSE_OP_NONE,
+        ]
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[green, red, transparent],
+            default_image=True,
+            disposal=disposal,
+            blend=PngImagePlugin.APNG_BLEND_OP_OVER,
+        )
+        with Image.open(test_file) as im:
+            im.seek(3)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        disposal = [
+            PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            PngImagePlugin.APNG_DISPOSE_OP_PREVIOUS,
+        ]
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[green],
+            disposal=disposal,
+            blend=PngImagePlugin.APNG_BLEND_OP_OVER,
+        )
+        with Image.open(test_file) as im:
+            im.seek(1)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+    def test_apng_save_blend(self):
+        test_file = self.tempfile("temp.png")
+        size = (128, 64)
+        red = Image.new("RGBA", size, (255, 0, 0, 255))
+        green = Image.new("RGBA", size, (0, 255, 0, 255))
+        transparent = Image.new("RGBA", size, (0, 0, 0, 0))
+
+        # test APNG_BLEND_OP_SOURCE on solid color
+        blend = [
+            PngImagePlugin.APNG_BLEND_OP_OVER,
+            PngImagePlugin.APNG_BLEND_OP_SOURCE,
+        ]
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[red, green],
+            default_image=True,
+            disposal=PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            blend=blend,
+        )
+        with Image.open(test_file) as im:
+            im.seek(2)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
+        # test APNG_BLEND_OP_SOURCE on transparent color
+        blend = [
+            PngImagePlugin.APNG_BLEND_OP_OVER,
+            PngImagePlugin.APNG_BLEND_OP_SOURCE,
+        ]
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[red, transparent],
+            default_image=True,
+            disposal=PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            blend=blend,
+        )
+        with Image.open(test_file) as im:
+            im.seek(2)
+            self.assertEqual(im.getpixel((0, 0)), (0, 0, 0, 0))
+            self.assertEqual(im.getpixel((64, 32)), (0, 0, 0, 0))
+
+        # test APNG_BLEND_OP_OVER
+        red.save(
+            test_file,
+            save_all=True,
+            append_images=[green, transparent],
+            default_image=True,
+            disposal=PngImagePlugin.APNG_DISPOSE_OP_NONE,
+            blend=PngImagePlugin.APNG_BLEND_OP_OVER,
+        )
+        with Image.open(test_file) as im:
+            im.seek(1)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+            im.seek(2)
+            self.assertEqual(im.getpixel((0, 0)), (0, 255, 0, 255))
+            self.assertEqual(im.getpixel((64, 32)), (0, 255, 0, 255))
+
 
 @unittest.skipIf(is_win32(), "requires Unix or macOS")
 @skip_unless_feature("zlib")