This patch allows a JPEG image to be saved with a specific qtables

value (in dictionary format).

Previously, this would throw a TypeError when checking if the qtables
value was actually a preset. By adding an isStringType check, we can
avoid this error.

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

@@ -230,6 +230,13 @@ def test_quality_keep():
     assert_no_exception(lambda: im.save(f, quality='keep'))
 
 
+def test_qtables():
+    im = Image.open("Images/lena.jpg")
+    qtables = im.quantization
+    f = tempfile('temp.jpg')
+    assert_no_exception(lambda: im.save(f, qtables=qtables, subsampling=0))
+
+
 def test_junk_jpeg_header():
     # https://github.com/python-imaging/Pillow/issues/630
     filename = "Tests/images/junk_jpeg_header.jpg"