Merge pull request #4989 from gofr/4962-jpeg-zigzag

De-zigzag JPEG's DQT when loading; deprecate convert_dict_qtables

Tests/test_file_jpeg.py

@@ -466,7 +466,7 @@ class TestFileJpeg:
                 assert len(im.quantization) == n
                 reloaded = self.roundtrip(im, qtables="keep")
                 assert im.quantization == reloaded.quantization
-                assert reloaded.quantization[0].typecode == "B"
+                assert max(reloaded.quantization[0]) <= 255
 
         with Image.open("Tests/images/hopper.jpg") as im:
             qtables = im.quantization
@@ -478,7 +478,8 @@ class TestFileJpeg:
 
             # valid bounds for baseline qtable
             bounds_qtable = [int(s) for s in ("255 1 " * 32).split(None)]
-            self.roundtrip(im, qtables=[bounds_qtable])
+            im2 = self.roundtrip(im, qtables=[bounds_qtable])
+            assert im2.quantization == {0: bounds_qtable}
 
             # values from wizard.txt in jpeg9-a src package.
             standard_l_qtable = [
@@ -589,6 +590,12 @@ class TestFileJpeg:
             assert max(im2.quantization[0]) <= 255
             assert max(im2.quantization[1]) <= 255
 
+    def test_convert_dict_qtables_deprecation(self):
+        with pytest.warns(DeprecationWarning):
+            qtable = {0: [1, 2, 3, 4]}
+            qtable2 = JpegImagePlugin.convert_dict_qtables(qtable)
+            assert qtable == qtable2
+
     @pytest.mark.skipif(not djpeg_available(), reason="djpeg not available")
     def test_load_djpeg(self):
         with Image.open(TEST_FILE) as img:

docs/deprecations.rst

@@ -25,26 +25,6 @@ vulnerability introduced in FreeType 2.6 (:cve:`CVE-2020-15999`).
 
 .. _2.10.4: https://sourceforge.net/projects/freetype/files/freetype2/2.10.4/
 
-Tk/Tcl 8.4
-~~~~~~~~~~
-
-.. deprecated:: 8.2.0
-
-Support for Tk/Tcl 8.4 is deprecated and will be removed in Pillow 10.0.0 (2023-01-02),
-when Tk/Tcl 8.5 will be the minimum supported.
-
-Categories
-~~~~~~~~~~
-
-.. deprecated:: 8.2.0
-
-``im.category`` is deprecated and will be removed in Pillow 10.0.0 (2023-01-02),
-along with the related ``Image.NORMAL``, ``Image.SEQUENCE`` and
-``Image.CONTAINER`` attributes.
-
-To determine if an image has multiple frames or not,
-``getattr(im, "is_animated", False)`` can be used instead.
-
 Image.show command parameter
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -82,6 +62,36 @@ Use ``__version__`` instead.
 It was initially removed in Pillow 7.0.0, but brought back in 7.1.0 to give projects
 more time to upgrade.
 
+Tk/Tcl 8.4
+~~~~~~~~~~
+
+.. deprecated:: 8.2.0
+
+Support for Tk/Tcl 8.4 is deprecated and will be removed in Pillow 10.0.0 (2023-01-02),
+when Tk/Tcl 8.5 will be the minimum supported.
+
+Categories
+~~~~~~~~~~
+
+.. deprecated:: 8.2.0
+
+``im.category`` is deprecated and will be removed in Pillow 10.0.0 (2023-01-02),
+along with the related ``Image.NORMAL``, ``Image.SEQUENCE`` and
+``Image.CONTAINER`` attributes.
+
+To determine if an image has multiple frames or not,
+``getattr(im, "is_animated", False)`` can be used instead.
+
+JpegImagePlugin.convert_dict_qtables
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 8.3.0
+
+JPEG ``quantization`` is now automatically converted, but still returned as a
+dictionary. The :py:attr:`~PIL.JpegImagePlugin.convert_dict_qtables` method no longer
+performs any operations on the data given to it, has been deprecated and will be
+removed in Pillow 10.0.0 (2023-01-02).
+
 Removed features
 ----------------
 

docs/releasenotes/8.3.0.rst

@@ -4,10 +4,13 @@
 Deprecations
 ============
 
-TODO
-^^^^
+JpegImagePlugin.convert_dict_qtables
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-TODO
+JPEG ``quantization`` is now automatically converted, but still returned as a
+dictionary. The :py:attr:`~PIL.JpegImagePlugin.convert_dict_qtables` method no longer
+performs any operations on the data given to it, has been deprecated and will be
+removed in Pillow 10.0.0 (2023-01-02).
 
 API Changes
 ===========

src/PIL/JpegImagePlugin.py

@@ -254,7 +254,7 @@ def DQT(self, marker):
         data = array.array("B" if precision == 1 else "H", s[1:qt_length])
         if sys.byteorder == "little" and precision > 1:
             data.byteswap()  # the values are always big-endian
-        self.quantization[v & 15] = data
+        self.quantization[v & 15] = [data[i] for i in zigzag_index]
         s = s[qt_length:]
 
 
@@ -601,9 +601,11 @@ samplings = {
 
 
 def convert_dict_qtables(qtables):
-    qtables = [qtables[key] for key in range(len(qtables)) if key in qtables]
-    for idx, table in enumerate(qtables):
-        qtables[idx] = [table[i] for i in zigzag_index]
+    warnings.warn(
+        "convert_dict_qtables is deprecated and will be removed in Pillow 10"
+        "(2023-01-02). Conversion is no longer needed.",
+        DeprecationWarning,
+    )
     return qtables
 
 
@@ -684,7 +686,9 @@ def _save(im, fp, filename):
                 qtables = [lines[s : s + 64] for s in range(0, len(lines), 64)]
         if isinstance(qtables, (tuple, list, dict)):
             if isinstance(qtables, dict):
-                qtables = convert_dict_qtables(qtables)
+                qtables = [
+                    qtables[key] for key in range(len(qtables)) if key in qtables
+                ]
             elif isinstance(qtables, tuple):
                 qtables = list(qtables)
             if not (0 < len(qtables) < 5):

src/PIL/JpegPresets.py

@@ -52,19 +52,11 @@ You can get the quantization tables of a JPEG with::
 
   im.quantization
 
-This will return a dict with a number of arrays. You can pass this dict
+This will return a dict with a number of lists. You can pass this dict
 directly as the qtables argument when saving a JPEG.
 
-The tables format between im.quantization and quantization in presets differ in
-3 ways:
-
-1. The base container of the preset is a list with sublists instead of dict.
-   dict[0] -> list[0], dict[1] -> list[1], ...
-2. Each table in a preset is a list instead of an array.
-3. The zigzag order is remove in the preset (needed by libjpeg >= 6a).
-
-You can convert the dict format to the preset format with the
-:func:`.JpegImagePlugin.convert_dict_qtables()` function.
+The quantization table format in presets is a list with sublists. These formats
+are interchangeable.
 
 Libjpeg ref.:
 https://web.archive.org/web/20120328125543/http://www.jpegcameras.com/libjpeg/libjpeg-3.html