Merge pull request #714 from wiredfool/jpeg_qtables

JPEG qtables

PIL/JpegImagePlugin.py

@@ -498,7 +498,7 @@ def _save(im, fp, filename):
     else:
         if subsampling in presets:
             subsampling = presets[subsampling].get('subsampling', -1)
-        if qtables in presets:
+        if isStringType(qtables) and qtables in presets:
             qtables = presets[qtables].get('quantization')
 
     if subsampling == "4:4:4":

Tests/test_file_jpeg.py

@@ -224,7 +224,57 @@ class TestFileJpeg(PillowTestCase):
         filename = "Tests/images/junk_jpeg_header.jpg"
         Image.open(filename)
 
+    def test_qtables(self):
+        im = Image.open("Tests/images/lena.jpg")
+        qtables = im.quantization
+        reloaded = self.roundtrip(im, qtables=qtables, subsampling=0)
+        self.assertEqual(im.quantization, reloaded.quantization)
+        self.assert_image_similar(im, self.roundtrip(im, qtables='web_low'), 30)
+        self.assert_image_similar(im, self.roundtrip(im, qtables='web_high'), 30)
+        self.assert_image_similar(im, self.roundtrip(im, qtables='keep'), 30)
 
+        #values from wizard.txt in jpeg9-a src package.
+        standard_l_qtable = [int(s) for s in """
+            16  11  10  16  24  40  51  61
+            12  12  14  19  26  58  60  55
+            14  13  16  24  40  57  69  56
+            14  17  22  29  51  87  80  62
+            18  22  37  56  68 109 103  77
+            24  35  55  64  81 104 113  92
+            49  64  78  87 103 121 120 101
+            72  92  95  98 112 100 103  99
+            """.split(None)]
+
+        standard_chrominance_qtable= [int(s) for s in """
+            17  18  24  47  99  99  99  99
+            18  21  26  66  99  99  99  99
+            24  26  56  99  99  99  99  99
+            47  66  99  99  99  99  99  99
+            99  99  99  99  99  99  99  99
+            99  99  99  99  99  99  99  99
+            99  99  99  99  99  99  99  99
+            99  99  99  99  99  99  99  99
+            """.split(None)]
+        # list of qtable lists
+        self.assert_image_similar(im,
+                                  self.roundtrip(im,
+                                                 qtables=[standard_l_qtable,
+                                                          standard_chrominance_qtable]),
+                                  30)
+        # tuple of qtable lists
+        self.assert_image_similar(im,
+                                  self.roundtrip(im,
+                                                 qtables=(standard_l_qtable,
+                                                          standard_chrominance_qtable)),
+                                  30)
+        # dict of qtable lists
+        self.assert_image_similar(im,
+                                  self.roundtrip(im,
+                                                 qtables={0:standard_l_qtable,
+                                                          1:standard_chrominance_qtable}),
+                                  30)
+        
+        
 if __name__ == '__main__':
     unittest.main()
 

docs/handbook/image-file-formats.rst

@@ -147,6 +147,29 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
     If present, indicates that this image should be stored as a progressive
     JPEG file.
 
+**subsampling**
+    If present, sets the subsampling for the encoder. 
+    
+    * ``keep``: Only valid for JPEG files, will retain the original image setting.
+    * ``4:4:4``, ``4:2:2``, ``4:1:1``: Specific sampling values
+    * ``-1``: equivalent to ``keep``
+    * ``0``: equivalent to ``4:4:4``
+    * ``1``: equivalent to ``4:2:2``
+    * ``2``: equivalent to ``4:1:1``
+
+**qtables**
+    If present, sets the qtables for the encoder. This is listed as an
+    advanced option for wizards in the JPEG documentation. Use with
+    caution. ``qtables`` can be one of several types of values:
+
+    *  a string, naming a preset, e.g. ``keep``, ``web_low``, or ``web_high``
+    *  a list, tuple, or dictionary (with integer keys =
+       range(len(keys))) of lists of 64 integers. There must be
+       between 2 and 4 tables. 
+
+    .. versionadded:: 2.5.0
+
+
 .. note::
 
     To enable JPEG support, you need to build and install the IJG JPEG library