diff --git a/PIL/PyAccess.py b/PIL/PyAccess.py
index d5acfd0fe..09ce86af4 100644
--- a/PIL/PyAccess.py
+++ b/PIL/PyAccess.py
@@ -133,6 +133,7 @@ class _PyAccess32_3(PyAccess):
         pixel.r = min(color[0], 255)
         pixel.g = min(color[1], 255)
         pixel.b = min(color[2], 255)
+        pixel.a = 255
 
 
 class _PyAccess32_4(PyAccess):
diff --git a/Tests/test_lib_pack.py b/Tests/test_lib_pack.py
index 83872c5d1..d062b33be 100644
--- a/Tests/test_lib_pack.py
+++ b/Tests/test_lib_pack.py
@@ -1,157 +1,481 @@
+import sys
+
 from helper import unittest, PillowTestCase, py3
 
 from PIL import Image
 
 
+X = 255
+
+
 class TestLibPack(PillowTestCase):
+    def assert_pack(self, mode, rawmode, data, *pixels):
+        """
+        data - either raw bytes with data or just number of bytes in rawmode.
+        """
+        im = Image.new(mode, (len(pixels), 1))
+        for x, pixel in enumerate(pixels):
+            im.putpixel((x, 0), pixel)
 
-    def pack(self):
-        pass  # not yet
+        if isinstance(data, (int)):
+            data_len = data * len(pixels)
+            data = bytes(bytearray(range(1, data_len + 1)))
 
-    def test_pack(self):
+        self.assertEqual(data, im.tobytes("raw", rawmode))
 
-        def pack(mode, rawmode, in_data=(1, 2, 3, 4)):
-            if len(mode) == 1:
-                im = Image.new(mode, (1, 1), in_data[0])
-            else:
-                im = Image.new(mode, (1, 1), in_data[:len(mode)])
+    def test_1(self):
+        self.assert_pack("1", "1", b'\x01', 0,0,0,0,0,0,0,X)
+        self.assert_pack("1", "1;I", b'\x01', X,X,X,X,X,X,X,0)
+        self.assert_pack("1", "1;R", b'\x01', X,0,0,0,0,0,0,0)
+        self.assert_pack("1", "1;IR", b'\x01', 0,X,X,X,X,X,X,X)
 
-            if py3:
-                return list(im.tobytes("raw", rawmode))
-            else:
-                return [ord(c) for c in im.tobytes("raw", rawmode)]
+        self.assert_pack("1", "1", b'\xaa', X,0,X,0,X,0,X,0)
+        self.assert_pack("1", "1;I", b'\xaa', 0,X,0,X,0,X,0,X)
+        self.assert_pack("1", "1;R", b'\xaa', 0,X,0,X,0,X,0,X)
+        self.assert_pack("1", "1;IR", b'\xaa', X,0,X,0,X,0,X,0)
 
-        order = 1 if Image._ENDIAN == '<' else -1
+        self.assert_pack("1", "L", b'\xff\x00\x00\xff\x00\x00', X,0,0,X,0,0)
 
-        self.assertEqual(pack("1", "1"), [128])
-        self.assertEqual(pack("1", "1;I"), [0])
-        self.assertEqual(pack("1", "1;R"), [1])
-        self.assertEqual(pack("1", "1;IR"), [0])
+    def test_L(self):
+        self.assert_pack("L", "L", 1, 1,2,3,4)
 
-        self.assertEqual(pack("L", "L"), [1])
+    def test_LA(self):
+        self.assert_pack("LA", "LA", 2, (1,2), (3,4), (5,6))
+        self.assert_pack("LA", "LA;L", 2, (1,4), (2,5), (3,6))
 
-        self.assertEqual(pack("I", "I"), [1, 0, 0, 0][::order])
+    def test_P(self):
+        self.assert_pack("P", "P;1", b'\xe4', 1, 1, 1, 0, 0, 255, 0, 0)
+        self.assert_pack("P", "P;2", b'\xe4', 3, 2, 1, 0)
+        self.assert_pack("P", "P;4", b'\x02\xef', 0, 2, 14, 15)
+        self.assert_pack("P", "P", 1, 1, 2, 3, 4)
 
-        self.assertEqual(pack("F", "F"), [0, 0, 128, 63][::order])
+    def test_PA(self):
+        self.assert_pack("PA", "PA", 2, (1,2), (3,4), (5,6))
+        self.assert_pack("PA", "PA;L", 2, (1,4), (2,5), (3,6))
 
-        self.assertEqual(pack("LA", "LA"), [1, 2])
+    def test_RGB(self):
+        self.assert_pack("RGB", "RGB", 3, (1,2,3), (4,5,6), (7,8,9))
+        self.assert_pack("RGB", "RGBX",
+            b'\x01\x02\x03\xff\x05\x06\x07\xff', (1,2,3), (5,6,7))
+        self.assert_pack("RGB", "XRGB",
+            b'\x00\x02\x03\x04\x00\x06\x07\x08', (2,3,4), (6,7,8))
+        self.assert_pack("RGB", "BGR", 3, (3,2,1), (6,5,4), (9,8,7))
+        self.assert_pack("RGB", "BGRX",
+            b'\x01\x02\x03\x00\x05\x06\x07\x00', (3,2,1), (7,6,5))
+        self.assert_pack("RGB", "XBGR",
+            b'\x00\x02\x03\x04\x00\x06\x07\x08', (4,3,2), (8,7,6))
+        self.assert_pack("RGB", "RGB;L", 3, (1,4,7), (2,5,8), (3,6,9))
+        self.assert_pack("RGB", "R", 1, (1,9,9), (2,9,9), (3,9,9))
+        self.assert_pack("RGB", "G", 1, (9,1,9), (9,2,9), (9,3,9))
+        self.assert_pack("RGB", "B", 1, (9,9,1), (9,9,2), (9,9,3))
 
-        self.assertEqual(pack("RGB", "RGB"), [1, 2, 3])
-        self.assertEqual(pack("RGB", "RGB;L"), [1, 2, 3])
-        self.assertEqual(pack("RGB", "BGR"), [3, 2, 1])
-        self.assertEqual(pack("RGB", "RGBX"), [1, 2, 3, 255])  # 255?
-        self.assertEqual(pack("RGB", "BGRX"), [3, 2, 1, 0])
-        self.assertEqual(pack("RGB", "XRGB"), [0, 1, 2, 3])
-        self.assertEqual(pack("RGB", "XBGR"), [0, 3, 2, 1])
+    def test_RGBA(self):
+        self.assert_pack("RGBA", "RGBA", 4,
+            (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_pack("RGBA", "RGBA;L", 4,
+            (1,4,7,10), (2,5,8,11), (3,6,9,12))
+        self.assert_pack("RGBA", "RGB", 3, (1,2,3,14), (4,5,6,15), (7,8,9,16))
+        self.assert_pack("RGBA", "BGR", 3, (3,2,1,14), (6,5,4,15), (9,8,7,16))
+        self.assert_pack("RGBA", "BGRA", 4,
+            (3,2,1,4), (7,6,5,8), (11,10,9,12))
+        self.assert_pack("RGBA", "ABGR", 4,
+            (4,3,2,1), (8,7,6,5), (12,11,10,9))
+        self.assert_pack("RGBA", "BGRa", 4,
+            (191,127,63,4), (223,191,159,8), (233,212,191,12))
+        self.assert_pack("RGBA", "R", 1, (1,0,8,9), (2,0,8,9), (3,0,8,0))
+        self.assert_pack("RGBA", "G", 1, (6,1,8,9), (6,2,8,9), (6,3,8,9))
+        self.assert_pack("RGBA", "B", 1, (6,7,1,9), (6,7,2,0), (6,7,3,9))
+        self.assert_pack("RGBA", "A", 1, (6,7,0,1), (6,7,0,2), (0,7,0,3))
 
-        self.assertEqual(pack("RGBX", "RGBX"), [1, 2, 3, 4])  # 4->255?
+    def test_RGBa(self):
+        self.assert_pack("RGBa", "RGBa", 4,
+            (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_pack("RGBa", "BGRa", 4,
+            (3,2,1,4), (7,6,5,8), (11,10,9,12))
+        self.assert_pack("RGBa", "aBGR", 4,
+            (4,3,2,1), (8,7,6,5), (12,11,10,9))
 
-        self.assertEqual(pack("RGBA", "RGBA"), [1, 2, 3, 4])
-        self.assertEqual(pack("RGBA", "BGRa"), [0, 0, 0, 4])
-        self.assertEqual(pack("RGBA", "BGRa", in_data=(20, 30, 40, 50)), [8, 6, 4, 50])
+    def test_RGBX(self):
+        self.assert_pack("RGBX", "RGBX", 4, (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_pack("RGBX", "RGBX;L", 4, (1,4,7,10), (2,5,8,11), (3,6,9,12))
+        self.assert_pack("RGBX", "RGB", 3, (1,2,3,X), (4,5,6,X), (7,8,9,X))
+        self.assert_pack("RGBX", "BGR", 3, (3,2,1,X), (6,5,4,X), (9,8,7,X))
+        self.assert_pack("RGBX", "BGRX",
+            b'\x01\x02\x03\x00\x05\x06\x07\x00\t\n\x0b\x00',
+            (3,2,1,X), (7,6,5,X), (11,10,9,X))
+        self.assert_pack("RGBX", "XBGR",
+            b'\x00\x02\x03\x04\x00\x06\x07\x08\x00\n\x0b\x0c',
+            (4,3,2,X), (8,7,6,X), (12,11,10,X))
+        self.assert_pack("RGBX", "R", 1, (1,0,8,9), (2,0,8,9), (3,0,8,0))
+        self.assert_pack("RGBX", "G", 1, (6,1,8,9), (6,2,8,9), (6,3,8,9))
+        self.assert_pack("RGBX", "B", 1, (6,7,1,9), (6,7,2,0), (6,7,3,9))
+        self.assert_pack("RGBX", "X", 1, (6,7,0,1), (6,7,0,2), (0,7,0,3))
 
-        self.assertEqual(pack("RGBa", "RGBa"), [1, 2, 3, 4])
-        self.assertEqual(pack("RGBa", "BGRa"), [3, 2, 1, 4])
-        self.assertEqual(pack("RGBa", "aBGR"), [4, 3, 2, 1])
+    def test_CMYK(self):
+        self.assert_pack("CMYK", "CMYK", 4, (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_pack("CMYK", "CMYK;I", 4,
+            (254,253,252,251), (250,249,248,247), (246,245,244,243))
+        self.assert_pack("CMYK", "CMYK;L", 4,
+            (1,4,7,10), (2,5,8,11), (3,6,9,12))
+        self.assert_pack("CMYK", "K", 1, (6,7,0,1), (6,7,0,2), (0,7,0,3))
 
-        self.assertEqual(pack("CMYK", "CMYK"), [1, 2, 3, 4])
-        self.assertEqual(pack("YCbCr", "YCbCr"), [1, 2, 3])
+    def test_YCbCr(self):
+        self.assert_pack("YCbCr", "YCbCr", 3, (1,2,3), (4,5,6), (7,8,9))
+        self.assert_pack("YCbCr", "YCbCr;L", 3, (1,4,7), (2,5,8), (3,6,9))
+        self.assert_pack("YCbCr", "YCbCrX",
+            b'\x01\x02\x03\xff\x05\x06\x07\xff\t\n\x0b\xff',
+            (1,2,3), (5,6,7), (9,10,11))
+        self.assert_pack("YCbCr", "YCbCrK",
+            b'\x01\x02\x03\xff\x05\x06\x07\xff\t\n\x0b\xff',
+            (1,2,3), (5,6,7), (9,10,11))
+        self.assert_pack("YCbCr", "Y", 1, (1,0,8,9), (2,0,8,9), (3,0,8,0))
+        self.assert_pack("YCbCr", "Cb", 1, (6,1,8,9), (6,2,8,9), (6,3,8,9))
+        self.assert_pack("YCbCr", "Cr", 1, (6,7,1,9), (6,7,2,0), (6,7,3,9))
 
-    def test_unpack(self):
+    def test_LAB(self):
+        self.assert_pack("LAB", "LAB", 3,
+            (1,130,131), (4,133,134), (7,136,137))
+        self.assert_pack("LAB", "L", 1, (1,9,9), (2,9,9), (3,9,9))
+        self.assert_pack("LAB", "A", 1, (9,1,9), (9,2,9), (9,3,9))
+        self.assert_pack("LAB", "B", 1, (9,9,1), (9,9,2), (9,9,3))
 
-        def unpack(mode, rawmode, bytes_):
-            im = None
+    def test_HSV(self):
+        self.assert_pack("HSV", "HSV", 3, (1,2,3), (4,5,6), (7,8,9))
+        self.assert_pack("HSV", "H", 1, (1,9,9), (2,9,9), (3,9,9))
+        self.assert_pack("HSV", "S", 1, (9,1,9), (9,2,9), (9,3,9))
+        self.assert_pack("HSV", "V", 1, (9,9,1), (9,9,2), (9,9,3))
 
-            if py3:
-                data = bytes(range(1, bytes_+1))
-            else:
-                data = ''.join(chr(i) for i in range(1, bytes_+1))
+    def test_I(self):
+        self.assert_pack("I", "I;16B", 2, 0x0102, 0x0304)
+        self.assert_pack("I", "I;32S",
+            b'\x83\x00\x00\x01\x01\x00\x00\x83',
+            0x01000083, -2097151999)
 
-            im = Image.frombytes(mode, (1, 1), data, "raw", rawmode, 0, 1)
+        if sys.byteorder == 'little':
+            self.assert_pack("I", "I", 4, 0x04030201, 0x08070605)
+            self.assert_pack("I", "I;32NS",
+                b'\x83\x00\x00\x01\x01\x00\x00\x83',
+                0x01000083, -2097151999)
+        else:
+            self.assert_pack("I", "I", 4, 0x01020304, 0x05060708)
+            self.assert_pack("I", "I;32NS",
+                b'\x83\x00\x00\x01\x01\x00\x00\x83',
+                -2097151999, 0x01000083)
 
-            return im.getpixel((0, 0))
+    def test_F_float(self):
+        self.assert_pack("F", "F;32F", 4,
+            1.539989614439558e-36, 4.063216068939723e-34)
 
-        def unpack_1(mode, rawmode, value):
-            assert mode == "1"
-            im = None
+        if sys.byteorder == 'little':
+            self.assert_pack("F", "F", 4,
+                1.539989614439558e-36, 4.063216068939723e-34)
+            self.assert_pack("F", "F;32NF", 4,
+                1.539989614439558e-36, 4.063216068939723e-34)
+        else:
+            self.assert_pack("F", "F", 4,
+                2.387939260590663e-38, 6.301941157072183e-36)
+            self.assert_pack("F", "F;32NF", 4,
+                2.387939260590663e-38, 6.301941157072183e-36)
 
-            if py3:
-                im = Image.frombytes(
-                    mode, (8, 1), bytes([value]), "raw", rawmode, 0, 1)
-            else:
-                im = Image.frombytes(
-                    mode, (8, 1), chr(value), "raw", rawmode, 0, 1)
 
-            return tuple(im.getdata())
+class TestLibUnpack(PillowTestCase):
+    def assert_unpack(self, mode, rawmode, data, *pixels):
+        """
+        data - either raw bytes with data or just number of bytes in rawmode.
+        """
+        if isinstance(data, (int)):
+            data_len = data * len(pixels)
+            data = bytes(bytearray(range(1, data_len + 1)))
 
-        X = 255
+        im = Image.frombytes(mode, (len(pixels), 1), data, "raw", rawmode, 0, 1)
 
-        self.assertEqual(unpack_1("1", "1", 1), (0, 0, 0, 0, 0, 0, 0, X))
-        self.assertEqual(unpack_1("1", "1;I", 1), (X, X, X, X, X, X, X, 0))
-        self.assertEqual(unpack_1("1", "1;R", 1), (X, 0, 0, 0, 0, 0, 0, 0))
-        self.assertEqual(unpack_1("1", "1;IR", 1), (0, X, X, X, X, X, X, X))
+        for x, pixel in enumerate(pixels):
+            self.assertEqual(pixel, im.getpixel((x, 0)))
 
-        self.assertEqual(unpack_1("1", "1", 170), (X, 0, X, 0, X, 0, X, 0))
-        self.assertEqual(unpack_1("1", "1;I", 170), (0, X, 0, X, 0, X, 0, X))
-        self.assertEqual(unpack_1("1", "1;R", 170), (0, X, 0, X, 0, X, 0, X))
-        self.assertEqual(unpack_1("1", "1;IR", 170), (X, 0, X, 0, X, 0, X, 0))
+    def test_1(self):
+        self.assert_unpack("1", "1", b'\x01', 0, 0, 0, 0, 0, 0, 0, X)
+        self.assert_unpack("1", "1;I", b'\x01', X, X, X, X, X, X, X, 0)
+        self.assert_unpack("1", "1;R", b'\x01', X, 0, 0, 0, 0, 0, 0, 0)
+        self.assert_unpack("1", "1;IR", b'\x01', 0, X, X, X, X, X, X, X)
 
-        self.assertEqual(unpack("L", "L;2", 1), 0)
-        self.assertEqual(unpack("L", "L;4", 1), 0)
-        self.assertEqual(unpack("L", "L", 1), 1)
-        self.assertEqual(unpack("L", "L;I", 1), 254)
-        self.assertEqual(unpack("L", "L;R", 1), 128)
-        self.assertEqual(unpack("L", "L;16", 2), 2)  # little endian
-        self.assertEqual(unpack("L", "L;16B", 2), 1)  # big endian
+        self.assert_unpack("1", "1", b'\xaa', X, 0, X, 0, X, 0, X, 0)
+        self.assert_unpack("1", "1;I", b'\xaa', 0, X, 0, X, 0, X, 0, X)
+        self.assert_unpack("1", "1;R", b'\xaa', 0, X, 0, X, 0, X, 0, X)
+        self.assert_unpack("1", "1;IR", b'\xaa', X, 0, X, 0, X, 0, X, 0)
 
-        self.assertEqual(unpack("LA", "LA", 2), (1, 2))
-        self.assertEqual(unpack("LA", "LA;L", 2), (1, 2))
+        self.assert_unpack("1", "1;8", b'\x00\x01\x02\xff', 0, X, X, X)
 
-        self.assertEqual(unpack("RGB", "RGB", 3), (1, 2, 3))
-        self.assertEqual(unpack("RGB", "RGB;L", 3), (1, 2, 3))
-        self.assertEqual(unpack("RGB", "RGB;R", 3), (128, 64, 192))
-        self.assertEqual(unpack("RGB", "RGB;16B", 6), (1, 3, 5))  # ?
-        self.assertEqual(unpack("RGB", "BGR", 3), (3, 2, 1))
-        self.assertEqual(unpack("RGB", "RGB;15", 2), (8, 131, 0))
-        self.assertEqual(unpack("RGB", "BGR;15", 2), (0, 131, 8))
-        self.assertEqual(unpack("RGB", "RGB;16", 2), (8, 64, 0))
-        self.assertEqual(unpack("RGB", "BGR;16", 2), (0, 64, 8))
-        self.assertEqual(unpack("RGB", "RGB;4B", 2), (17, 0, 34))
+    def test_L(self):
+        self.assert_unpack("L", "L;2", b'\xe4', 255, 170, 85, 0)
+        self.assert_unpack("L", "L;2I", b'\xe4', 0, 85, 170, 255)
+        self.assert_unpack("L", "L;2R", b'\xe4', 0, 170, 85, 255)
+        self.assert_unpack("L", "L;2IR", b'\xe4', 255, 85, 170, 0)
 
-        self.assertEqual(unpack("RGB", "RGBX", 4), (1, 2, 3))
-        self.assertEqual(unpack("RGB", "BGRX", 4), (3, 2, 1))
-        self.assertEqual(unpack("RGB", "XRGB", 4), (2, 3, 4))
-        self.assertEqual(unpack("RGB", "XBGR", 4), (4, 3, 2))
+        self.assert_unpack("L", "L;4", b'\x02\xef', 0, 34, 238, 255)
+        self.assert_unpack("L", "L;4I", b'\x02\xef', 255, 221, 17, 0)
+        self.assert_unpack("L", "L;4R", b'\x02\xef', 68, 0, 255, 119)
+        self.assert_unpack("L", "L;4IR", b'\x02\xef', 187, 255, 0, 136)
 
-        self.assertEqual(unpack("RGBA", "RGBA", 4), (1, 2, 3, 4))
-        self.assertEqual(unpack("RGBA", "RGBa", 4), (63, 127, 191, 4))
-        self.assertEqual(unpack("RGBA", "BGRA", 4), (3, 2, 1, 4))
-        self.assertEqual(unpack("RGBA", "BGRa", 4), (191, 127, 63, 4))
-        self.assertEqual(unpack("RGBA", "ARGB", 4), (2, 3, 4, 1))
-        self.assertEqual(unpack("RGBA", "ABGR", 4), (4, 3, 2, 1))
-        self.assertEqual(unpack("RGBA", "RGBA;15", 2), (8, 131, 0, 0))
-        self.assertEqual(unpack("RGBA", "BGRA;15", 2), (0, 131, 8, 0))
-        self.assertEqual(unpack("RGBA", "RGBA;4B", 2), (17, 0, 34, 0))
+        self.assert_unpack("L", "L", 1, 1, 2, 3, 4)
+        self.assert_unpack("L", "L;I", 1, 254, 253, 252, 251)
+        self.assert_unpack("L", "L;R", 1, 128, 64, 192, 32)
+        self.assert_unpack("L", "L;16", 2, 2, 4, 6, 8)
+        self.assert_unpack("L", "L;16B", 2, 1, 3, 5, 7)
 
-        self.assertEqual(unpack("RGBa", "RGBa", 4), (1, 2, 3, 4))
-        self.assertEqual(unpack("RGBa", "BGRa", 4), (3, 2, 1, 4))
-        self.assertEqual(unpack("RGBa", "aRGB", 4), (2, 3, 4, 1))
-        self.assertEqual(unpack("RGBa", "aBGR", 4), (4, 3, 2, 1))
+    def test_LA(self):
+        self.assert_unpack("LA", "LA", 2, (1, 2), (3, 4), (5, 6))
+        self.assert_unpack("LA", "LA;L", 2, (1, 4), (2, 5), (3, 6))
 
-        self.assertEqual(unpack("RGBX", "RGBX", 4), (1, 2, 3, 4))  # 4->255?
-        self.assertEqual(unpack("RGBX", "BGRX", 4), (3, 2, 1, 255))
-        self.assertEqual(unpack("RGBX", "XRGB", 4), (2, 3, 4, 255))
-        self.assertEqual(unpack("RGBX", "XBGR", 4), (4, 3, 2, 255))
-        self.assertEqual(unpack("RGBX", "RGB;15", 2), (8, 131, 0, 255))
-        self.assertEqual(unpack("RGBX", "BGR;15", 2), (0, 131, 8, 255))
-        self.assertEqual(unpack("RGBX", "RGB;4B", 2), (17, 0, 34, 255))
+    def test_P(self):
+        self.assert_unpack("P", "P;1", b'\xe4', 1, 1, 1, 0, 0, 1, 0, 0)
+        self.assert_unpack("P", "P;2", b'\xe4', 3, 2, 1, 0)
+        # self.assert_unpack("P", "P;2L", b'\xe4', 1, 1, 1, 0)  # erroneous?
+        self.assert_unpack("P", "P;4", b'\x02\xef', 0, 2, 14, 15)
+        # self.assert_unpack("P", "P;4L", b'\x02\xef', 2, 10, 10, 0)  # erroneous?
+        self.assert_unpack("P", "P", 1, 1, 2, 3, 4)
+        self.assert_unpack("P", "P;R", 1, 128, 64, 192, 32)
 
-        self.assertEqual(unpack("CMYK", "CMYK", 4), (1, 2, 3, 4))
-        self.assertEqual(unpack("CMYK", "CMYK;I", 4), (254, 253, 252, 251))
+    def test_PA(self):
+        self.assert_unpack("PA", "PA", 2, (1, 2), (3, 4), (5, 6))
+        self.assert_unpack("PA", "PA;L", 2, (1, 4), (2, 5), (3, 6))
 
-        self.assertRaises(ValueError, lambda: unpack("L", "L", 0))
-        self.assertRaises(ValueError, lambda: unpack("RGB", "RGB", 2))
-        self.assertRaises(ValueError, lambda: unpack("CMYK", "CMYK", 2))
+    def test_RGB(self):
+        self.assert_unpack("RGB", "RGB", 3, (1,2,3), (4,5,6), (7,8,9))
+        self.assert_unpack("RGB", "RGB;L", 3, (1,4,7), (2,5,8), (3,6,9))
+        self.assert_unpack("RGB", "RGB;R", 3, (128,64,192), (32,160,96))
+        self.assert_unpack("RGB", "RGB;16B", 6, (1,3,5), (7,9,11))
+        self.assert_unpack("RGB", "BGR", 3, (3,2,1), (6,5,4), (9,8,7))
+        self.assert_unpack("RGB", "RGB;15", 2, (8,131,0), (24,0,8))
+        self.assert_unpack("RGB", "BGR;15", 2, (0,131,8), (8,0,24))
+        self.assert_unpack("RGB", "RGB;16", 2, (8,64,0), (24,129,0))
+        self.assert_unpack("RGB", "BGR;16", 2, (0,64,8), (0,129,24))
+        self.assert_unpack("RGB", "RGB;4B", 2, (17,0,34), (51,0,68))
+        self.assert_unpack("RGB", "RGBX", 4, (1,2,3), (5,6,7), (9,10,11))
+        self.assert_unpack("RGB", "RGBX;L", 4, (1,4,7), (2,5,8), (3,6,9))
+        self.assert_unpack("RGB", "BGRX", 4, (3,2,1), (7,6,5), (11,10,9))
+        self.assert_unpack("RGB", "XRGB", 4, (2,3,4), (6,7,8), (10,11,12))
+        self.assert_unpack("RGB", "XBGR", 4, (4,3,2), (8,7,6), (12,11,10))
+        self.assert_unpack("RGB", "YCC;P",
+            b'D]\x9c\x82\x1a\x91\xfaOC\xe7J\x12',  # random data
+            (127,102,0), (192,227,0), (213,255,170), (98,255,133))
+        self.assert_unpack("RGB", "R", 1, (1,0,0), (2,0,0), (3,0,0))
+        self.assert_unpack("RGB", "G", 1, (0,1,0), (0,2,0), (0,3,0))
+        self.assert_unpack("RGB", "B", 1, (0,0,1), (0,0,2), (0,0,3))
+
+    def test_RGBA(self):
+        self.assert_unpack("RGBA", "LA", 2, (1,1,1,2), (3,3,3,4), (5,5,5,6))
+        self.assert_unpack("RGBA", "LA;16B", 4,
+            (1,1,1,3), (5,5,5,7), (9,9,9,11))
+        self.assert_unpack("RGBA", "RGBA", 4,
+            (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_unpack("RGBA", "RGBa", 4,
+            (63,127,191,4), (159,191,223,8), (191,212,233,12))
+        self.assert_unpack("RGBA", "BGRa", 4,
+            (191,127,63,4), (223,191,159,8), (233,212,191,12))
+        self.assert_unpack("RGBA", "RGBA;I", 4,
+            (254,253,252,4), (250,249,248,8), (246,245,244,12))
+        self.assert_unpack("RGBA", "RGBA;L", 4,
+            (1,4,7,10), (2,5,8,11), (3,6,9,12))
+        self.assert_unpack("RGBA", "RGBA;15", 2, (8,131,0,0), (24,0,8,0))
+        self.assert_unpack("RGBA", "BGRA;15", 2, (0,131,8,0), (8,0,24,0))
+        self.assert_unpack("RGBA", "RGBA;4B", 2, (17,0,34,0), (51,0,68,0))
+        self.assert_unpack("RGBA", "RGBA;16B", 8, (1,3,5,7), (9,11,13,15))
+        self.assert_unpack("RGBA", "BGRA", 4,
+            (3,2,1,4), (7,6,5,8), (11,10,9,12))
+        self.assert_unpack("RGBA", "ARGB", 4,
+            (2,3,4,1), (6,7,8,5), (10,11,12,9))
+        self.assert_unpack("RGBA", "ABGR", 4,
+            (4,3,2,1), (8,7,6,5), (12,11,10,9))
+        self.assert_unpack("RGBA", "YCCA;P",
+            b']bE\x04\xdd\xbej\xed57T\xce\xac\xce:\x11',  # random data
+            (0,161,0,4), (255,255,255,237), (27,158,0,206), (0,118,0,17))
+        self.assert_unpack("RGBA", "R", 1, (1,0,0,0), (2,0,0,0), (3,0,0,0))
+        self.assert_unpack("RGBA", "G", 1, (0,1,0,0), (0,2,0,0), (0,3,0,0))
+        self.assert_unpack("RGBA", "B", 1, (0,0,1,0), (0,0,2,0), (0,0,3,0))
+        self.assert_unpack("RGBA", "A", 1, (0,0,0,1), (0,0,0,2), (0,0,0,3))
+
+    def test_RGBa(self):
+        self.assert_unpack("RGBa", "RGBa", 4,
+            (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_unpack("RGBa", "BGRa", 4,
+            (3,2,1,4), (7,6,5,8), (11,10,9,12))
+        self.assert_unpack("RGBa", "aRGB", 4,
+            (2,3,4,1), (6,7,8,5), (10,11,12,9))
+        self.assert_unpack("RGBa", "aBGR", 4,
+            (4,3,2,1), (8,7,6,5), (12,11,10,9))
+
+    def test_RGBX(self):
+        self.assert_unpack("RGBX", "RGB", 3, (1,2,3,X), (4,5,6,X), (7,8,9,X))
+        self.assert_unpack("RGBX", "RGB;L", 3, (1,4,7,X), (2,5,8,X), (3,6,9,X))
+        self.assert_unpack("RGBX", "RGB;16B", 6, (1,3,5,X), (7,9,11,X))
+        self.assert_unpack("RGBX", "BGR", 3, (3,2,1,X), (6,5,4,X), (9,8,7,X))
+        self.assert_unpack("RGBX", "RGB;15", 2, (8,131,0,X), (24,0,8,X))
+        self.assert_unpack("RGBX", "BGR;15", 2, (0,131,8,X), (8,0,24,X))
+        self.assert_unpack("RGBX", "RGB;4B", 2, (17,0,34,X), (51,0,68,X))
+        self.assert_unpack("RGBX", "RGBX", 4,
+            (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_unpack("RGBX", "RGBX;L", 4,
+            (1,4,7,10), (2,5,8,11), (3,6,9,12))
+        self.assert_unpack("RGBX", "BGRX", 4, (3,2,1,X), (7,6,5,X), (11,10,9,X))
+        self.assert_unpack("RGBX", "XRGB", 4, (2,3,4,X), (6,7,8,X), (10,11,12,X))
+        self.assert_unpack("RGBX", "XBGR", 4, (4,3,2,X), (8,7,6,X), (12,11,10,X))
+        self.assert_unpack("RGBX", "YCC;P",
+            b'D]\x9c\x82\x1a\x91\xfaOC\xe7J\x12',  # random data
+            (127,102,0,X), (192,227,0,X), (213,255,170,X), (98,255,133,X))
+        self.assert_unpack("RGBX", "R", 1, (1,0,0,0), (2,0,0,0), (3,0,0,0))
+        self.assert_unpack("RGBX", "G", 1, (0,1,0,0), (0,2,0,0), (0,3,0,0))
+        self.assert_unpack("RGBX", "B", 1, (0,0,1,0), (0,0,2,0), (0,0,3,0))
+        self.assert_unpack("RGBX", "X", 1, (0,0,0,1), (0,0,0,2), (0,0,0,3))
+
+    def test_CMYK(self):
+        self.assert_unpack("CMYK", "CMYK", 4, (1,2,3,4), (5,6,7,8), (9,10,11,12))
+        self.assert_unpack("CMYK", "CMYK;I", 4,
+            (254,253,252,251), (250,249,248,247), (246,245,244,243))
+        self.assert_unpack("CMYK", "CMYK;L", 4,
+            (1,4,7,10), (2,5,8,11), (3,6,9,12))
+        self.assert_unpack("CMYK", "C", 1, (1,0,0,0), (2,0,0,0), (3,0,0,0))
+        self.assert_unpack("CMYK", "M", 1, (0,1,0,0), (0,2,0,0), (0,3,0,0))
+        self.assert_unpack("CMYK", "Y", 1, (0,0,1,0), (0,0,2,0), (0,0,3,0))
+        self.assert_unpack("CMYK", "K", 1, (0,0,0,1), (0,0,0,2), (0,0,0,3))
+        self.assert_unpack("CMYK", "C;I", 1,
+            (254,0,0,0), (253,0,0,0), (252,0,0,0))
+        self.assert_unpack("CMYK", "M;I", 1,
+            (0,254,0,0), (0,253,0,0), (0,252,0,0))
+        self.assert_unpack("CMYK", "Y;I", 1,
+            (0,0,254,0), (0,0,253,0), (0,0,252,0))
+        self.assert_unpack("CMYK", "K;I", 1,
+            (0,0,0,254), (0,0,0,253), (0,0,0,252))
+
+    def test_YCbCr(self):
+        self.assert_unpack("YCbCr", "YCbCr", 3, (1,2,3), (4,5,6), (7,8,9))
+        self.assert_unpack("YCbCr", "YCbCr;L", 3, (1,4,7), (2,5,8), (3,6,9))
+        self.assert_unpack("YCbCr", "YCbCrX", 4, (1,2,3), (5,6,7), (9,10,11))
+        self.assert_unpack("YCbCr", "YCbCrK", 4, (1,2,3), (5,6,7), (9,10,11))
+
+    def test_LAB(self):
+        self.assert_unpack("LAB", "LAB", 3,
+            (1,130,131), (4,133,134), (7,136,137))
+        self.assert_unpack("LAB", "L", 1, (1,0,0), (2,0,0), (3,0,0))
+        self.assert_unpack("LAB", "A", 1, (0,1,0), (0,2,0), (0,3,0))
+        self.assert_unpack("LAB", "B", 1, (0,0,1), (0,0,2), (0,0,3))
+
+    def test_HSV(self):
+        self.assert_unpack("HSV", "HSV", 3, (1,2,3), (4,5,6), (7,8,9))
+        self.assert_unpack("HSV", "H", 1, (1,0,0), (2,0,0), (3,0,0))
+        self.assert_unpack("HSV", "S", 1, (0,1,0), (0,2,0), (0,3,0))
+        self.assert_unpack("HSV", "V", 1, (0,0,1), (0,0,2), (0,0,3))
+
+    def test_I(self):
+        self.assert_unpack("I", "I;8", 1, 0x01, 0x02, 0x03, 0x04)
+        self.assert_unpack("I", "I;8S", b'\x01\x83', 1, -125)
+        self.assert_unpack("I", "I;16", 2, 0x0201, 0x0403)
+        self.assert_unpack("I", "I;16S", b'\x83\x01\x01\x83', 0x0183, -31999)
+        self.assert_unpack("I", "I;16B", 2, 0x0102, 0x0304)
+        self.assert_unpack("I", "I;16BS", b'\x83\x01\x01\x83', -31999, 0x0183)
+        self.assert_unpack("I", "I;32", 4, 0x04030201, 0x08070605)
+        self.assert_unpack("I", "I;32S",
+            b'\x83\x00\x00\x01\x01\x00\x00\x83',
+            0x01000083, -2097151999)
+        self.assert_unpack("I", "I;32B", 4, 0x01020304, 0x05060708)
+        self.assert_unpack("I", "I;32BS",
+            b'\x83\x00\x00\x01\x01\x00\x00\x83',
+            -2097151999, 0x01000083)
+
+        if sys.byteorder == 'little':
+            self.assert_unpack("I", "I", 4, 0x04030201, 0x08070605)
+            self.assert_unpack("I", "I;16N", 2, 0x0201, 0x0403)
+            self.assert_unpack("I", "I;16NS", b'\x83\x01\x01\x83', 0x0183, -31999)
+            self.assert_unpack("I", "I;32N", 4, 0x04030201, 0x08070605)
+            self.assert_unpack("I", "I;32NS",
+                b'\x83\x00\x00\x01\x01\x00\x00\x83',
+                0x01000083, -2097151999)
+        else:
+            self.assert_unpack("I", "I", 4, 0x01020304, 0x05060708)
+            self.assert_unpack("I", "I;16N", 2, 0x0102, 0x0304)
+            self.assert_unpack("I", "I;16NS", b'\x83\x01\x01\x83', -31999, 0x0183)
+            self.assert_unpack("I", "I;32N", 4, 0x01020304, 0x05060708)
+            self.assert_unpack("I", "I;32NS",
+                b'\x83\x00\x00\x01\x01\x00\x00\x83',
+                -2097151999, 0x01000083)
+
+    def test_F_int(self):
+        self.assert_unpack("F", "F;8", 1, 0x01, 0x02, 0x03, 0x04)
+        self.assert_unpack("F", "F;8S", b'\x01\x83', 1, -125)
+        self.assert_unpack("F", "F;16", 2, 0x0201, 0x0403)
+        self.assert_unpack("F", "F;16S", b'\x83\x01\x01\x83', 0x0183, -31999)
+        self.assert_unpack("F", "F;16B", 2, 0x0102, 0x0304)
+        self.assert_unpack("F", "F;16BS", b'\x83\x01\x01\x83', -31999, 0x0183)
+        self.assert_unpack("F", "F;32", 4, 67305984, 134678016)
+        self.assert_unpack("F", "F;32S",
+            b'\x83\x00\x00\x01\x01\x00\x00\x83',
+            16777348, -2097152000)
+        self.assert_unpack("F", "F;32B", 4, 0x01020304, 0x05060708)
+        self.assert_unpack("F", "F;32BS",
+            b'\x83\x00\x00\x01\x01\x00\x00\x83',
+            -2097152000, 16777348)
+
+        if sys.byteorder == 'little':
+            self.assert_unpack("F", "F;16N", 2, 0x0201, 0x0403)
+            self.assert_unpack("F", "F;16NS", b'\x83\x01\x01\x83', 0x0183, -31999)
+            self.assert_unpack("F", "F;32N", 4, 67305984, 134678016)
+            self.assert_unpack("F", "F;32NS",
+                b'\x83\x00\x00\x01\x01\x00\x00\x83',
+                16777348, -2097152000)
+        else:
+            self.assert_unpack("F", "F;16N", 2, 0x0102, 0x0304)
+            self.assert_unpack("F", "F;16NS", b'\x83\x01\x01\x83', -31999, 0x0183)
+            self.assert_unpack("F", "F;32N", 4, 0x01020304, 0x05060708)
+            self.assert_unpack("F", "F;32NS",
+                b'\x83\x00\x00\x01\x01\x00\x00\x83',
+                -2097152000, 16777348)
+
+    def test_F_float(self):
+        self.assert_unpack("F", "F;32F", 4,
+            1.539989614439558e-36, 4.063216068939723e-34)
+        self.assert_unpack("F", "F;32BF", 4,
+            2.387939260590663e-38, 6.301941157072183e-36)
+        self.assert_unpack("F", "F;64F",
+            b'333333\xc3?\x00\x00\x00\x00\x00J\x93\xc0',  # by struct.pack
+            0.15000000596046448, -1234.5)
+        self.assert_unpack("F", "F;64BF",
+            b'?\xc3333333\xc0\x93J\x00\x00\x00\x00\x00',  # by struct.pack
+            0.15000000596046448, -1234.5)
+
+        if sys.byteorder == 'little':
+            self.assert_unpack("F", "F", 4,
+                1.539989614439558e-36, 4.063216068939723e-34)
+            self.assert_unpack("F", "F;32NF", 4,
+                1.539989614439558e-36, 4.063216068939723e-34)
+            self.assert_unpack("F", "F;64NF",
+                b'333333\xc3?\x00\x00\x00\x00\x00J\x93\xc0',
+                0.15000000596046448, -1234.5)
+        else:
+            self.assert_unpack("F", "F", 4,
+                2.387939260590663e-38, 6.301941157072183e-36)
+            self.assert_unpack("F", "F;32NF", 4,
+                2.387939260590663e-38, 6.301941157072183e-36)
+            self.assert_unpack("F", "F;64NF",
+                b'?\xc3333333\xc0\x93J\x00\x00\x00\x00\x00',
+                0.15000000596046448, -1234.5)
+
+    def test_I16(self):
+        self.assert_unpack("I;16", "I;16", 2, 0x0201, 0x0403, 0x0605)
+        self.assert_unpack("I;16B", "I;16B", 2, 0x0102, 0x0304, 0x0506)
+        self.assert_unpack("I;16L", "I;16L", 2, 0x0201, 0x0403, 0x0605)
+        self.assert_unpack("I;16", "I;12", 2, 0x0010, 0x0203, 0x0040, 0x0506)
+        if sys.byteorder == 'little':
+            self.assert_unpack("I;16", "I;16N", 2, 0x0201, 0x0403, 0x0605)
+            self.assert_unpack("I;16B", "I;16N", 2, 0x0201, 0x0403, 0x0605)
+            self.assert_unpack("I;16L", "I;16N", 2, 0x0201, 0x0403, 0x0605)
+        else:
+            self.assert_unpack("I;16", "I;16N", 2, 0x0102, 0x0304, 0x0506)
+            self.assert_unpack("I;16B", "I;16N", 2, 0x0102, 0x0304, 0x0506)
+            self.assert_unpack("I;16L", "I;16N", 2, 0x0102, 0x0304, 0x0506)
+
+    def test_value_error(self):
+        self.assertRaises(ValueError, self.assert_unpack, "L", "L", 0, 0)
+        self.assertRaises(ValueError, self.assert_unpack, "RGB", "RGB", 2, 0)
+        self.assertRaises(ValueError, self.assert_unpack, "CMYK", "CMYK", 2, 0)
 
 
 if __name__ == '__main__':
diff --git a/libImaging/Pack.c b/libImaging/Pack.c
index 621936351..0810f51f1 100644
--- a/libImaging/Pack.c
+++ b/libImaging/Pack.c
@@ -559,8 +559,8 @@ static struct {
     /* true colour w. padding */
     {"RGBX",    "RGBX",         32,     copy4},
     {"RGBX",    "RGBX;L",       32,     packRGBXL},
-    {"RGBX",    "RGB",          32,     ImagingPackRGB},
-    {"RGBX",    "BGR",          32,     ImagingPackBGR},
+    {"RGBX",    "RGB",          24,     ImagingPackRGB},
+    {"RGBX",    "BGR",          24,     ImagingPackBGR},
     {"RGBX",    "BGRX",         32,     ImagingPackBGRX},
     {"RGBX",    "XBGR",         32,     ImagingPackXBGR},
     {"RGBX",    "R",            8,      band0},
diff --git a/libImaging/Unpack.c b/libImaging/Unpack.c
index 05f98095d..ce47a5727 100644
--- a/libImaging/Unpack.c
+++ b/libImaging/Unpack.c
@@ -1176,6 +1176,8 @@ static struct {
        endian byte order (default is little endian); "L" line
        interleave, "S" signed, "F" floating point */
 
+    /* exception: rawmodes "I" and "F" are always native endian byte order */
+
     /* bilevel */
     {"1",       "1",            1,      unpack1},
     {"1",       "1;I",          1,      unpack1I},