imaging.images2swf — GRASS Python Library documentation

# Source code for imaging.images2swf

    #   Copyright (C) 2012, Almar Klein
    #
    #   This code is subject to the (new) BSD license:
    #
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    #     * Redistributions of source code must retain the above copyright
    #       notice, this list of conditions and the following disclaimer.
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    #     * Neither the name of the <organization> nor the
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    #       derived from this software without specific prior written permission.
    #
    # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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    """ Module images2swf

    Provides a function (writeSwf) to store a series of PIL images or numpy
    arrays in an SWF movie, that can be played on a wide range of OS's.

    This module came into being because I wanted to store a series of images
    in a movie that can be viewed by other people, and which I can embed in
    flash presentations. For writing AVI or MPEG you really need a c/c++
    library, and although the filesize is then very small, the quality is
    sometimes not adequate. Besides I'd like to be independent of yet another
    package. I tried writing animated gif using PIL (which is widely available),
    but the quality is so poor because it only allows for 256 different colors.
    [EDIT: thanks to Ant1, now the quality of animated gif isn't so bad!]
    I also looked into MNG and APNG, two standards similar to the PNG stanard.
    Both standards promise exactly what I need. However, hardly any application
    can read those formats, and I cannot import them in flash.

    Therefore I decided to check out the swf file format, which is very well
    documented. This is the result: a pure python module to create an SWF file
    that shows a series of images. The images are stored using the DEFLATE
    algorithm (same as PNG and ZIP and which is included in the standard Python
    distribution). As this compression algorithm is much more effective than
    that used in GIF images, we obtain better quality (24 bit colors + alpha
    channel) while still producesing smaller files (a test showed ~75%).
    Although SWF also allows for JPEG compression, doing so would probably
    require a third party library (because encoding JPEG is much harder).

    This module requires Python 2.x and numpy.

    sources and tools:

    - SWF on wikipedia
    - Adobes "SWF File Format Specification" version 10
      (http://www.adobe.com/devnet/swf/pdf/swf_file_format_spec_v10.pdf)
    - swftools (swfdump in specific) for debugging
    - iwisoft swf2avi can be used to convert swf to avi/mpg/flv with really
      good quality, while file size is reduced with factors 20-100.
      A good program in my opinion. The free version has the limitation
      of a watermark in the upper left corner.

    """

    import os
    import zlib

    try:
        import numpy as np
    except ImportError:
        np = None

    try:
        import PIL.Image
    except ImportError:
        PIL = None

    string_types = (str,)
    integer_types = (int,)
    class_types = (type,)
    text_type = str
    binary_type = bytes

    # todo: use imageio/FreeImage to support reading JPEG images from SWF?

    def checkImages(images):
        """checkImages(images)
        Check numpy images and correct intensity range etc.
        The same for all movie formats.
        """
        # Init results
        images2 = []

        for im in images:
            if PIL and isinstance(im, PIL.Image.Image):
                # We assume PIL images are alright
                images2.append(im)

            elif np and isinstance(im, np.ndarray):
                # Check and convert dtype
                if im.dtype == np.uint8:
                    images2.append(im)  # Ok
                elif im.dtype in [np.float32, np.float64]:
                    theMax = im.max()
                    if theMax > 128 and theMax < 300:
                        pass  # assume 0:255
                    else:
                        im = im.copy()
                        im[im < 0] = 0
                        im[im > 1] = 1
                        im *= 255
                    images2.append(im.astype(np.uint8))
                else:
                    im = im.astype(np.uint8)
                    images2.append(im)
                # Check size
                if im.ndim == 2:
                    pass  # ok
                elif im.ndim == 3:
                    if im.shape[2] not in [3, 4]:
                        raise ValueError("This array can not represent an image.")
                else:
                    raise ValueError("This array can not represent an image.")
            else:
                raise ValueError("Invalid image type: " + str(type(im)))

        # Done
        return images2

    # Base functions and classes

    class BitArray:
        """Dynamic array of bits that automatically resizes
        with factors of two.
        Append bits using .Append() or +=
        You can reverse bits using .Reverse()
        """

        def __init__(self, initvalue=None):
            self.data = np.zeros((16,), dtype=np.uint8)
            self._len = 0
            if initvalue is not None:
                self.Append(initvalue)

        def __len__(self):
            return self._len  # self.data.shape[0]

        def __repr__(self):
            return self.data[: self._len].tobytes()

        def _checkSize(self):
            # check length... grow if necessary
            arraylen = self.data.shape[0]
            if self._len >= arraylen:
                tmp = np.zeros((arraylen * 2,), dtype=np.uint8)
                tmp[: self._len] = self.data[: self._len]
                self.data = tmp

        def __add__(self, value):
            self.Append(value)
            return self

        def Append(self, bits):
            # check input
            if isinstance(bits, BitArray):
                bits = str(bits)
            if isinstance(bits, int):
                bits = str(bits)
            if not isinstance(bits, string_types):
                raise ValueError("Append bits as strings or integers!")

            # add bits
            for bit in bits:
                self.data[self._len] = ord(bit)
                self._len += 1
                self._checkSize()

        def Reverse(self):
            """In-place reverse."""
            tmp = self.data[: self._len].copy()
            self.data[: self._len] = np.flipud(tmp)

        def ToBytes(self):
            """Convert to bytes. If necessary,
            zeros are padded to the end (right side).
            """
            bits = str(self)

            # determine number of bytes
            nbytes = 0
            while nbytes * 8 < len(bits):
                nbytes += 1
            # pad
            bits = bits.ljust(nbytes * 8, "0")

            # go from bits to bytes
            bb = binary_type()
            for i in range(nbytes):
                tmp = int(bits[i * 8 : (i + 1) * 8], 2)
                bb += intToUint8(tmp)

            # done
            return bb

    def intToUint32(i):
        return int(i).to_bytes(4, "little")

    def intToUint16(i):
        return int(i).to_bytes(2, "little")

    def intToUint8(i):
        return int(i).to_bytes(1, "little")

    def intToBits(i, n=None):
        """convert int to a string of bits (0's and 1's in a string),
        pad to n elements. Convert back using int(ss,2)."""
        ii = i

        # make bits
        bb = BitArray()
        while ii > 0:
            bb += str(ii % 2)
            ii = ii >> 1
        bb.Reverse()

        # justify
        if n is not None:
            if len(bb) > n:
                raise ValueError("intToBits fail: len larger than padlength.")
            bb = str(bb).rjust(n, "0")

        # done
        return BitArray(bb)

    def bitsToInt(bb, n=8):
        # Init
        value = ""

        # Get value in bits
        for i in range(len(bb)):
            b = bb[i : i + 1]
            tmp = bin(ord(b))[2:]
            # value += tmp.rjust(8,'0')
            value = tmp.rjust(8, "0") + value

        # Make decimal
        return int(value[:n], 2)

    def getTypeAndLen(bb):
        """bb should be 6 bytes at least
        Return (type, length, length_of_full_tag)
        """
        # Init
        value = ""

        # Get first 16 bits
        for i in range(2):
            b = bb[i : i + 1]
            tmp = bin(ord(b))[2:]
            # value += tmp.rjust(8,'0')
            value = tmp.rjust(8, "0") + value

        # Get type and length
        type = int(value[:10], 2)
        L = int(value[10:], 2)
        L2 = L + 2

        # Long tag header?
        if L == 63:  # '111111'
            value = ""
            for i in range(2, 6):
                b = bb[i : i + 1]  # becomes a single-byte bytes() on both PY3 and PY2
                tmp = bin(ord(b))[2:]
                # value += tmp.rjust(8,'0')
                value = tmp.rjust(8, "0") + value
            L = int(value, 2)
            L2 = L + 6

        # Done
        return type, L, L2

    def signedIntToBits(i, n=None):
        """convert signed int to a string of bits (0's and 1's in a string),
        pad to n elements. Negative numbers are stored in 2's complement bit
        patterns, thus positive numbers always start with a 0.
        """

        # negative number?
        ii = i
        if i < 0:
            # A negative number, -n, is represented as the bitwise opposite of
            ii = abs(ii) - 1  # the positive-zero number n-1.

        # make bits
        bb = BitArray()
        while ii > 0:
            bb += str(ii % 2)
            ii = ii >> 1
        bb.Reverse()

        # justify
        bb = "0" + str(bb)  # always need the sign bit in front
        if n is not None:
            if len(bb) > n:
                raise ValueError("signedIntToBits fail: len larger than padlength.")
            bb = bb.rjust(n, "0")

        # was it negative? (then opposite bits)
        if i < 0:
            bb = bb.replace("0", "x").replace("1", "0").replace("x", "1")

        # done
        return BitArray(bb)

    def twitsToBits(arr):
        """Given a few (signed) numbers, store them
        as compactly as possible in the wat specifief by the swf format.
        The numbers are multiplied by 20, assuming they
        are twits.
        Can be used to make the RECT record.
        """

        # first determine length using non justified bit strings
        maxlen = 1
        for i in arr:
            tmp = len(signedIntToBits(i * 20))
            if tmp > maxlen:
                maxlen = tmp

        # build array
        bits = intToBits(maxlen, 5)
        for i in arr:
            bits += signedIntToBits(i * 20, maxlen)

        return bits

    def floatsToBits(arr):
        """Given a few (signed) numbers, convert them to bits,
        stored as FB (float bit values). We always use 16.16.
        Negative numbers are not (yet) possible, because I don't
        know how the're implemented (ambiguity).
        """
        bits = intToBits(31, 5)  # 32 does not fit in 5 bits!
        for i in arr:
            if i < 0:
                raise ValueError("Dit not implement negative floats!")
            i1 = int(i)
            i2 = i - i1
            bits += intToBits(i1, 15)
            bits += intToBits(i2 * 2**16, 16)
        return bits

    def _readFrom(fp, n):
        bb = binary_type()
        try:
            while len(bb) < n:
                tmp = fp.read(n - len(bb))
                bb += tmp
                if not tmp:
                    break
        except EOFError:
            pass
        return bb

    # Base Tag

    class Tag:
        def __init__(self):
            self.bytes = binary_type()
            self.tagtype = -1

        def ProcessTag(self):
            """Implement this to create the tag."""
            raise NotImplementedError()

        def GetTag(self):
            """Calls processTag and attaches the header."""
            self.ProcessTag()

            # tag to binary
            bits = intToBits(self.tagtype, 10)

            # complete header uint16 thing
            bits += "1" * 6  # = 63 = 0x3f
            # make uint16
            bb = intToUint16(int(str(bits), 2))

            # now add 32bit length descriptor
            bb += intToUint32(len(self.bytes))

            # done, attach and return
            bb += self.bytes
            return bb

        def MakeRectRecord(self, xmin, xmax, ymin, ymax):
            """Simply uses makeCompactArray to produce
            a RECT Record."""
            return twitsToBits([xmin, xmax, ymin, ymax])

        def MakeMatrixRecord(self, scale_xy=None, rot_xy=None, trans_xy=None):
            # empty matrix?
            if scale_xy is None and rot_xy is None and trans_xy is None:
                return "0" * 8

            # init
            bits = BitArray()

            # scale
            if scale_xy:
                bits += "1"
                bits += floatsToBits([scale_xy[0], scale_xy[1]])
            else:
                bits += "0"

            # rotation
            if rot_xy:
                bits += "1"
                bits += floatsToBits([rot_xy[0], rot_xy[1]])
            else:
                bits += "0"

            # translation (no flag here)
            if trans_xy:
                bits += twitsToBits([trans_xy[0], trans_xy[1]])
            else:
                bits += twitsToBits([0, 0])

            # done
            return bits

    # Control tags

    class ControlTag(Tag):
        def __init__(self):
            Tag.__init__(self)

    class FileAttributesTag(ControlTag):
        def __init__(self):
            ControlTag.__init__(self)
            self.tagtype = 69

        def ProcessTag(self):
            self.bytes = "\x00".encode("ascii") * (1 + 3)

    class ShowFrameTag(ControlTag):
        def __init__(self):
            ControlTag.__init__(self)
            self.tagtype = 1

        def ProcessTag(self):
            self.bytes = binary_type()

    class SetBackgroundTag(ControlTag):
        """Set the color in 0-255, or 0-1 (if floats given)."""

        def __init__(self, *rgb):
            self.tagtype = 9
            if len(rgb) == 1:
                rgb = rgb[0]
            self.rgb = rgb

        def ProcessTag(self):
            bb = binary_type()
            for i in range(3):
                clr = self.rgb[i]
                if isinstance(clr, float):
                    clr = clr * 255
                bb += intToUint8(clr)
            self.bytes = bb

    class DoActionTag(Tag):
        def __init__(self, action="stop"):
            Tag.__init__(self)
            self.tagtype = 12
            self.actions = [action]

        def Append(self, action):
            self.actions.append(action)

        def ProcessTag(self):
            bb = binary_type()

            for action in self.actions:
                action = action.lower()
                if action == "stop":
                    bb += "\x07".encode("ascii")
                elif action == "play":
                    bb += "\x06".encode("ascii")
                else:
                    print("warning, unknown action: %s" % action)

            bb += intToUint8(0)
            self.bytes = bb

    # Definition tags

    class DefinitionTag(Tag):
        counter = 0  # to give automatically id's

        def __init__(self):
            Tag.__init__(self)
            DefinitionTag.counter += 1
            self.id = DefinitionTag.counter  # id in dictionary

    class BitmapTag(DefinitionTag):
        def __init__(self, im):
            DefinitionTag.__init__(self)
            self.tagtype = 36  # DefineBitsLossless2

            # convert image (note that format is ARGB)
            # even a grayscale image is stored in ARGB, nevertheless,
            # the fabilous deflate compression will make it that not much
            # more data is required for storing (25% or so, and less than 10%
            # when storing RGB as ARGB).

            if len(im.shape) == 3:
                if im.shape[2] in [3, 4]:
                    tmp = np.ones((im.shape[0], im.shape[1], 4), dtype=np.uint8) * 255
                    for i in range(3):
                        tmp[:, :, i + 1] = im[:, :, i]
                    if im.shape[2] == 4:
                        tmp[:, :, 0] = im[:, :, 3]  # swap channel where alpha is in
                else:
                    raise ValueError("Invalid shape to be an image.")

            elif len(im.shape) == 2:
                tmp = np.ones((im.shape[0], im.shape[1], 4), dtype=np.uint8) * 255
                for i in range(3):
                    tmp[:, :, i + 1] = im[:, :]
            else:
                raise ValueError("Invalid shape to be an image.")

            # we changed the image to uint8 4 channels.
            # now compress!
            self._data = zlib.compress(tmp.tostring(), zlib.DEFLATED)
            self.imshape = im.shape

        def ProcessTag(self):
            # build tag
            bb = binary_type()
            bb += intToUint16(self.id)  # CharacterID
            bb += intToUint8(5)  # BitmapFormat
            bb += intToUint16(self.imshape[1])  # BitmapWidth
            bb += intToUint16(self.imshape[0])  # BitmapHeight
            bb += self._data  # ZlibBitmapData

            self.bytes = bb

    class PlaceObjectTag(ControlTag):
        def __init__(self, depth, idToPlace=None, xy=(0, 0), move=False):
            ControlTag.__init__(self)
            self.tagtype = 26
            self.depth = depth
            self.idToPlace = idToPlace
            self.xy = xy
            self.move = move

        def ProcessTag(self):
            # retrieve stuff
            depth = self.depth
            xy = self.xy
            id = self.idToPlace

            # build PlaceObject2
            bb = binary_type()
            if self.move:
                bb += "\x07".encode("ascii")
            else:
                bb += "\x06".encode("ascii")  # (8 bit flags): 4:matrix, 2:character, 1:move
            bb += intToUint16(depth)  # Depth
            bb += intToUint16(id)  # character id
            bb += self.MakeMatrixRecord(trans_xy=xy).ToBytes()  # MATRIX record
            self.bytes = bb

    class ShapeTag(DefinitionTag):
        def __init__(self, bitmapId, xy, wh):
            DefinitionTag.__init__(self)
            self.tagtype = 2
            self.bitmapId = bitmapId
            self.xy = xy
            self.wh = wh

        def ProcessTag(self):
            """Returns a defineshape tag. with a bitmap fill"""

            bb = binary_type()
            bb += intToUint16(self.id)
            xy, wh = self.xy, self.wh
            tmp = self.MakeRectRecord(xy[0], wh[0], xy[1], wh[1])  # ShapeBounds
            bb += tmp.ToBytes()

            # make SHAPEWITHSTYLE structure

            # first entry: FILLSTYLEARRAY with in it a single fill style
            bb += intToUint8(1)  # FillStyleCount
            bb += "\x41".encode(
                "ascii"
            )  # FillStyleType  (0x41 or 0x43, latter is non-smoothed)
            bb += intToUint16(self.bitmapId)  # BitmapId
            # bb += '\x00' # BitmapMatrix (empty matrix with leftover bits filled)
            bb += self.MakeMatrixRecord(scale_xy=(20, 20)).ToBytes()

            #         # first entry: FILLSTYLEARRAY with in it a single fill style
            #         bb += intToUint8(1)  # FillStyleCount
            #         bb += '\x00' # solid fill
            #         bb += '\x00\x00\xff' # color

            # second entry: LINESTYLEARRAY with a single line style
            bb += intToUint8(0)  # LineStyleCount
            # bb += intToUint16(0*20) # Width
            # bb += '\x00\xff\x00'  # Color

            # third and fourth entry: NumFillBits and NumLineBits (4 bits each)
            # I each give them four bits, so 16 styles possible.
            bb += "\x44".encode("ascii")

            self.bytes = bb

            # last entries: SHAPERECORDs ... (individual shape records not aligned)
            # STYLECHANGERECORD
            bits = BitArray()
            bits += self.MakeStyleChangeRecord(0, 1, moveTo=(self.wh[0], self.wh[1]))
            # STRAIGHTEDGERECORD 4x
            bits += self.MakeStraightEdgeRecord(-self.wh[0], 0)
            bits += self.MakeStraightEdgeRecord(0, -self.wh[1])
            bits += self.MakeStraightEdgeRecord(self.wh[0], 0)
            bits += self.MakeStraightEdgeRecord(0, self.wh[1])

            # ENDSHAPRECORD
            bits += self.MakeEndShapeRecord()

            self.bytes += bits.ToBytes()

            # done
            # self.bytes = bb

        def MakeStyleChangeRecord(self, lineStyle=None, fillStyle=None, moveTo=None):
            # first 6 flags
            # Note that we use FillStyle1. If we don't flash (at least 8) does not
            # recognize the frames properly when importing to library.

            bits = BitArray()
            bits += "0"  # TypeFlag (not an edge record)
            bits += "0"  # StateNewStyles (only for DefineShape2 and Defineshape3)
            if lineStyle:
                bits += "1"  # StateLineStyle
            else:
                bits += "0"
            if fillStyle:
                bits += "1"  # StateFillStyle1
            else:
                bits += "0"
            bits += "0"  # StateFillStyle0
            if moveTo:
                bits += "1"  # StateMoveTo
            else:
                bits += "0"

            # give information
            # todo: nbits for fillStyle and lineStyle is hard coded.

            if moveTo:
                bits += twitsToBits([moveTo[0], moveTo[1]])
            if fillStyle:
                bits += intToBits(fillStyle, 4)
            if lineStyle:
                bits += intToBits(lineStyle, 4)

            return bits

            # return bitsToBytes(bits)

        def MakeStraightEdgeRecord(self, *dxdy):
            if len(dxdy) == 1:
                dxdy = dxdy[0]

            # determine required number of bits
            xbits = signedIntToBits(dxdy[0] * 20)
            ybits = signedIntToBits(dxdy[1] * 20)
            nbits = max([len(xbits), len(ybits)])

            bits = BitArray()
            bits += "11"  # TypeFlag and StraightFlag
            bits += intToBits(nbits - 2, 4)
            bits += "1"  # GeneralLineFlag
            bits += signedIntToBits(dxdy[0] * 20, nbits)
            bits += signedIntToBits(dxdy[1] * 20, nbits)

            # note: I do not make use of vertical/horizontal only lines...

            return bits

            # return bitsToBytes(bits)

        def MakeEndShapeRecord(self):
            bits = BitArray()
            bits += "0"  # TypeFlag: no edge
            bits += "0" * 5  # EndOfShape
            return bits

            # return bitsToBytes(bits)

    # Last few functions

    def buildFile(fp, taglist, nframes=1, framesize=(500, 500), fps=10, version=8):
        """Give the given file (as bytes) a header."""

        # compose header
        bb = binary_type()
        bb += "F".encode("ascii")  # uncompressed
        bb += "WS".encode("ascii")  # signature bytes
        bb += intToUint8(version)  # version
        bb += "0000".encode("ascii")  # FileLength (leave open for now)
        bb += Tag().MakeRectRecord(0, framesize[0], 0, framesize[1]).ToBytes()
        bb += intToUint8(0) + intToUint8(fps)  # FrameRate
        bb += intToUint16(nframes)
        fp.write(bb)

        # produce all tags
        for tag in taglist:
            fp.write(tag.GetTag())

        # finish with end tag
        fp.write("\x00\x00".encode("ascii"))

        # set size
        sze = fp.tell()
        fp.seek(4)
        fp.write(intToUint32(sze))

    def writeSwf(filename, images, duration=0.1, repeat=True):
        """Write an swf-file from the specified images. If repeat is False,
        the movie is finished with a stop action. Duration may also
        be a list with durations for each frame (note that the duration
        for each frame is always an integer amount of the minimum duration.)

        Images should be a list consisting of PIL images or numpy arrays.
        The latter should be between 0 and 255 for integer types, and
        between 0 and 1 for float types.

        """

        # Check Numpy
        if np is None:
            raise RuntimeError("Need Numpy to write an SWF file.")

        # Check images (make all Numpy)
        images2 = []
        images = checkImages(images)
        if not images:
            raise ValueError("Image list is empty!")
        for im in images:
            if PIL and isinstance(im, PIL.Image.Image):
                if im.mode == "P":
                    im = im.convert()
                im = np.asarray(im)
                if len(im.shape) == 0:
                    raise MemoryError("Too little memory to convert PIL image to array")
            images2.append(im)

        # Init
        taglist = [FileAttributesTag(), SetBackgroundTag(0, 0, 0)]

        # Check duration
        if hasattr(duration, "__len__"):
            if len(duration) == len(images2):
                duration = [d for d in duration]
            else:
                raise ValueError("len(duration) doesn't match amount of images.")
        else:
            duration = [duration for im in images2]

        # Build delays list
        minDuration = float(min(duration))
        delays = [round(d / minDuration) for d in duration]
        delays = [max(1, int(d)) for d in delays]

        # Get FPS
        fps = 1.0 / minDuration

        # Produce series of tags for each image
        nframes = 0
        for im in images2:
            bm = BitmapTag(im)
            wh = (im.shape[1], im.shape[0])
            sh = ShapeTag(bm.id, (0, 0), wh)
            po = PlaceObjectTag(1, sh.id, move=nframes > 0)
            taglist.extend([bm, sh, po])
            for i in range(delays[nframes]):
                taglist.append(ShowFrameTag())
            nframes += 1

        if not repeat:
            taglist.append(DoActionTag("stop"))

        # Build file
        fp = open(filename, "wb")
        try:
            buildFile(fp, taglist, nframes=nframes, framesize=wh, fps=fps)
        except Exception:
            raise
        finally:
            fp.close()

    def _readPixels(bb, i, tagType, L1):
        """With pf's seed after the recordheader, reads the pixeldata."""

        # Check Numpy
        if np is None:
            raise RuntimeError("Need Numpy to read an SWF file.")

        # Get info
        # charId = bb[i : i + 2]  # unused
        i += 2
        format = ord(bb[i : i + 1])
        i += 1
        width = bitsToInt(bb[i : i + 2], 16)
        i += 2
        height = bitsToInt(bb[i : i + 2], 16)
        i += 2

        # If we can, get pixeldata and make numpy array
        if format != 5:
            print("Can only read 24bit or 32bit RGB(A) lossless images.")
        else:
            # Read byte data
            offset = 2 + 1 + 2 + 2  # all the info bits
            bb2 = bb[i : i + (L1 - offset)]

            # Decompress and make numpy array
            data = zlib.decompress(bb2)
            a = np.frombuffer(data, dtype=np.uint8)

            # Set shape
            if tagType == 20:
                # DefineBitsLossless - RGB data
                try:
                    a.shape = height, width, 3
                except Exception:
                    # Byte align stuff might cause troubles
                    print("Cannot read image due to byte alignment")
            if tagType == 36:
                # DefineBitsLossless2 - ARGB data
                a.shape = height, width, 4
                # Swap alpha channel to make RGBA
                b = a
                a = np.zeros_like(a)
                a[:, :, 0] = b[:, :, 1]
                a[:, :, 1] = b[:, :, 2]
                a[:, :, 2] = b[:, :, 3]
                a[:, :, 3] = b[:, :, 0]

            return a

    def readSwf(filename, asNumpy=True):
        """Read all images from an SWF (shockwave flash) file. Returns a list
        of numpy arrays, or, if asNumpy is false, a list if PIL images.

        Limitation: only read the PNG encoded images (not the JPG encoded ones).

        """

        # Check whether it exists
        if not os.path.isfile(filename):
            raise OSError("File not found: " + str(filename))

        # Check PIL
        if (not asNumpy) and (PIL is None):
            raise RuntimeError("Need PIL to return as PIL images.")

        # Check Numpy
        if np is None:
            raise RuntimeError("Need Numpy to read SWF files.")

        # Init images
        images = []

        # Open file and read all
        fp = open(filename, "rb")
        bb = fp.read()

        try:
            # Check opening tag
            tmp = bb[0:3].decode("ascii", "ignore")
            if tmp.upper() == "FWS":
                pass  # ok
            elif tmp.upper() == "CWS":
                # Decompress movie
                bb = bb[:8] + zlib.decompress(bb[8:])
            else:
                raise OSError("Not a valid SWF file: " + str(filename))

            # Set filepointer at first tag (skipping framesize RECT and two uin16's
            i = 8
            nbits = bitsToInt(bb[i : i + 1], 5)  # skip FrameSize
            nbits = 5 + nbits * 4
            Lrect = nbits / 8.0
            if Lrect % 1:
                Lrect += 1
            Lrect = int(Lrect)
            i += Lrect + 4

            # Iterate over the tags
            counter = 0
            while True:
                counter += 1

                # Get tag header
                head = bb[i : i + 6]
                if not head:
                    break  # Done (we missed end tag)

                # Determine type and length
                T, L1, L2 = getTypeAndLen(head)
                if not L2:
                    print("Invalid tag length, could not proceed")
                    break
                # print(T, L2)

                # Read image if we can
                if T in [20, 36]:
                    im = _readPixels(bb, i + 6, T, L1)
                    if im is not None:
                        images.append(im)
                elif T in [6, 21, 35, 90]:
                    print("Ignoring JPEG image: cannot read JPEG.")
                else:
                    pass  # Not an image tag

                # Detect end tag
                if T == 0:
                    break

                # Next tag!
                i += L2

        finally:
            fp.close()

        # Convert to normal PIL images if needed
        if not asNumpy:
            images2 = images
            images = []
            for im in images2:
                images.append(PIL.Image.fromarray(im))

        # Done
        return images

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