Basic MPO reading works, seek is partially there.

PIL/Image.py

@@ -2231,7 +2231,6 @@ def open(fp, mode="r"):
 
     for i in ID:
         try:
-            print(ID)
             factory, accept = OPEN[i]
             if not accept or accept(prefix):
                 fp.seek(0)

PIL/JpegImagePlugin.py

@@ -37,6 +37,7 @@ __version__ = "0.6"
 import array
 import struct
 import io
+from struct import unpack
 from PIL import Image, ImageFile, TiffImagePlugin, _binary
 from PIL.JpegPresets import presets
 from PIL._util import isStringType
@@ -114,6 +115,7 @@ def APP(self, marker):
     elif marker == 0xFFE2 and s[:4] == b"MPF\0":
         # extract MPO information
         self.info["mp"] = s[4:]
+        self.info["mpoffset"] = self.fp.tell()
 
 
 def COM(self, marker):
@@ -451,12 +453,30 @@ def _getmp(self):
         return None
     file = io.BytesIO(data)
     head = file.read(8)
+    endianness = '>' if head[:4] == b'\x4d\x4d\x00\x2a' else '<'
     mp = {}
     # process dictionary
     info = TiffImagePlugin.ImageFileDirectory(head)
     info.load(file)
     for key, value in info.items():
         mp[key] = _fixup(value)
+    # it's an error not to have a number of images
+    try:
+        quant = mp[0xB001]
+    except KeyError:
+        raise SyntaxError("malformed MP Index (no number of images)")
+    # get MP entries
+    try:
+        mpentries = []
+        for entrynum in range(0, quant):
+            rawmpentry = mp[0xB002][entrynum * 16:(entrynum + 1) * 16]
+            unpackedentry = unpack('{0}LLLHH'.format(endianness), rawmpentry)
+            labels = ('Attribute', 'Size', 'DataOffset', 'EntryNo1', 'EntryNo2')
+            mpentry = dict(zip(labels, unpackedentry))
+            mpentries.append(mpentry)
+        mp[0xB002] = mpentries
+    except KeyError:
+        raise SyntaxError("malformed MP Index (bad MP Entry)")
     return mp
 
 

PIL/MpoImagePlugin.py

@@ -38,21 +38,28 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
 
     def _open(self):
         JpegImagePlugin.JpegImageFile._open(self)
+        self.mpinfo = self._getmp()
+        self.__framecount = self.mpinfo[0xB001]
+        self.__mpoffsets = [mpent['DataOffset'] + self.info['mpoffset'] \
+            for mpent in self.mpinfo[0xB002]]
+        assert self.__framecount == len(self.__mpoffsets)
+        del self.info['mpoffset'] # no longer needed
         self.__fp = self.fp # FIXME: hack
-        self.__rewind = self.fp.tell()
-        self.seek(0) # get ready to read first frame
+        self.__fp.seek(self.__mpoffsets[0]) # get ready to read first frame
+        self.__frame = 0
+        self.offset = 0
 
     def seek(self, frame):
-
-        if frame == 0:
-            # rewind
-            self.__offset = 0
-            self.dispose = None
-            self.__frame = -1
-            self.__fp.seek(self.__rewind)
-
-        if frame != self.__frame + 1:
-            raise ValueError("cannot seek to frame %d" % frame)
+        if frame < 0 or frame >= self.__framecount:
+            raise EOFError("no more images in MPO file")
+        else:
+            self.fp = self.__fp
+            self.fp.seek(self.__mpoffsets[frame])
+            self.offset = self.__mpoffsets[frame]
+            rawmode = self.mode
+            if self.mode == "CMYK":
+                rawmode = "CMYK;I"  # assume adobe conventions
+            self.tile = [("jpeg", (0, 0) + self.size, 0, (rawmode, ""))]
         self.__frame = frame
 
     def tell(self):

Tests/test_file_mpo.py

@@ -54,6 +54,26 @@ class TestFileMpo(PillowTestCase):
             info = im._getmp()
             self.assertEqual(info[45056], '0100')
             self.assertEqual(info[45057], 2)
+    
+    def test_seek(self):
+        for test_file in test_files:
+            im = Image.open(test_file)
+            self.assertEqual(im.tell(), 0)
+            # prior to first image raises an error, both blatant and borderline
+            self.assertRaises(EOFError, im.seek, -1)
+            self.assertRaises(EOFError, im.seek, -523)
+            # after the final image raises an error, both blatant and borderline
+            self.assertRaises(EOFError, im.seek, 2)
+            self.assertRaises(EOFError, im.seek, 523)
+            # bad calls shouldn't change the frame
+            self.assertEqual(im.tell(), 0)
+            # this one will work
+            im.seek(1)
+            self.assertEqual(im.tell(), 1)
+            # and this one, too
+            im.seek(0)
+            self.assertEqual(im.tell(), 0)
+            
 
 if __name__ == '__main__':
     unittest.main()