multiPageTiff.py

# AppendingTiffWriter
# -*- coding: utf-8 -*-
#
# "file object wrapper class" that is able to append a TIF to an existing one
#
# Code by @vashek (https://github.com/vashek) published at
# https://github.com/python-pillow/Pillow/issues/733#issuecomment-249380397
#
# Fixed PEP8 and clean by Jesús Leganés-Combarro 'piranna' <piranna@gmail.com>

from enum import IntEnum
from io import open, SEEK_CUR, SEEK_END, SEEK_SET
from struct import pack, unpack

try:
    from logging import trace
except ImportError as e:
    def trace(*args, **kwargs):
        pass


class AppendingTiffWriter:
    fieldSizes = [
        0,  # None
        1,  # byte
        1,  # ascii
        2,  # short
        4,  # long
        8,  # rational
        1,  # sbyte
        1,  # undefined
        2,  # sshort
        4,  # slong
        8,  # srational
        4,  # float
        8,  # double
    ]

    class Tags(IntEnum):
        StripOffsets = 273
        FreeOffsets = 288
        TileOffsets = 324
        JPEGQTables = 519
        JPEGDCTables = 520
        JPEGACTables = 521

    def __init__(self, fn, new=False):
        self.whereToWriteNewIFDOffset = None
        self.offsetOfNewPage = 0
        self.name = fn

        mode = "w+b" if new else "r+b"

        if hasattr(fn, 'read'):
            self.f = fn
        else:
            try:
                self.f = open(fn, mode)
            except IOError:
                self.f = open(fn, "w+b")

        self.IIMM = IIMM = self.f.read(4)
        if not IIMM:
            # empty file - first page
            self.isFirst = True
            return

        self.isFirst = False
        if IIMM == "II\x2a\x00":
            self.setEndian("<")
        elif IIMM == "MM\x00\x2a":
            self.setEndian(">")
        else:
            raise RuntimeError("Invalid TIFF file header")

        self.skipIFDs()
        self.goToEnd()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.close()
        return False

    def tell(self):
        return self.f.tell() - self.offsetOfNewPage

    def seek(self, offset, whence):
        if whence == SEEK_SET:
            offset += self.offsetOfNewPage

        self.f.seek(offset, whence)
        return self.tell()

    def goToEnd(self):
        self.f.seek(0, SEEK_END)
        pos = self.f.tell()

        # pad to 16 byte boundary
        padBytes = 16 - pos % 16
        if 0 < padBytes < 16:
            self.f.write(bytes(bytearray(padBytes)))
        self.offsetOfNewPage = self.f.tell()

    def setEndian(self, endian):
        self.endian = endian
        self.longFmt = self.endian + "L"
        self.shortFmt = self.endian + "H"
        self.tagFormat = self.endian + "HHL"

    def skipIFDs(self):
        while True:
            IFDoffset = self.readLong()
            if IFDoffset == 0:
                self.whereToWriteNewIFDOffset = self.f.tell() - 4
                break

            self.f.seek(IFDoffset)
            numTags = self.readShort()
            self.f.seek(numTags * 12, SEEK_CUR)

    def write(self, data):
        return self.f.write(data)

    def readShort(self):
        value, = unpack(self.shortFmt, self.f.read(2))
        return value

    def readLong(self):
        value, = unpack(self.longFmt, self.f.read(4))
        return value

    def rewriteLastShortToLong(self, value):
        self.f.seek(-2, SEEK_CUR)
        bytesWritten = self.f.write(pack(self.longFmt, value))
        if bytesWritten != 4:
            raise RuntimeError("wrote only %u bytes but wanted 4" %
                               bytesWritten)

    def rewriteLastShort(self, value):
        self.f.seek(-2, SEEK_CUR)
        bytesWritten = self.f.write(pack(self.shortFmt, value))
        if bytesWritten != 2:
            raise RuntimeError("wrote only %u bytes but wanted 2" %
                               bytesWritten)

    def rewriteLastLong(self, value):
        self.f.seek(-4, SEEK_CUR)
        bytesWritten = self.f.write(pack(self.longFmt, value))
        if bytesWritten != 4:
            raise RuntimeError("wrote only %u bytes but wanted 4" %
                               bytesWritten)

    def writeShort(self, value):
        bytesWritten = self.f.write(pack(self.shortFmt, value))
        if bytesWritten != 2:
            raise RuntimeError("wrote only %u bytes but wanted 2" %
                               bytesWritten)

    def writeLong(self, value):
        bytesWritten = self.f.write(pack(self.longFmt, value))
        if bytesWritten != 4:
            raise RuntimeError("wrote only %u bytes but wanted 4" %
                               bytesWritten)

    def close(self):
        if not self.isFirst:
            # fix offsets
            self.f.seek(self.offsetOfNewPage)

            IIMM = self.f.read(4)
            if not IIMM:
                raise RuntimeError("nothing written into new page")
            if IIMM != self.IIMM:
                raise RuntimeError("IIMM of new page doesn't match IIMM of "
                                   "first page")

            IFDoffset = self.readLong()
            IFDoffset += self.offsetOfNewPage
            self.f.seek(self.whereToWriteNewIFDOffset)
            self.writeLong(IFDoffset)
            self.f.seek(IFDoffset)
            self.fixIFD()

        self.f.close()

    def fixIFD(self):
        numTags = self.readShort()
        trace("fixing IFD at %X; number of tags: %u (0x%X)", self.f.tell()-2,
              numTags, numTags)

        edit_tags = set(self.Tags)

        for i in range(numTags):
            tag, fieldType, count = unpack(self.tagFormat, self.f.read(8))
            trace("  at %X: tag %u (0x%X), type %u, count %u", self.f.tell()-8,
                  tag, tag, fieldType, count)

            fieldSize = self.fieldSizes[fieldType]
            totalSize = fieldSize * count
            isLocal = (totalSize <= 4)
            if not isLocal:
                offset = self.readLong()
                offset += self.offsetOfNewPage
                self.rewriteLastLong(offset)

            if tag in edit_tags:
                curPos = self.f.tell()

                if isLocal:
                    self.fixOffsets(count, isShort=(fieldSize == 2),
                                    isLong=(fieldSize == 4))
                    self.f.seek(curPos + 4)
                else:
                    self.f.seek(offset)
                    self.fixOffsets(count, isShort=(fieldSize == 2),
                                    isLong=(fieldSize == 4))
                    self.f.seek(curPos)

                offset = curPos = None

            elif isLocal:
                # skip the locally stored value that is not an offset
                self.f.seek(4, SEEK_CUR)

    def fixOffsets(self, count, isShort=False, isLong=False):
        if not isShort and not isLong:
            raise RuntimeError("offset is neither short nor long")

        for i in range(count):
            offset = self.readShort() if isShort else self.readLong()
            offset += self.offsetOfNewPage
            if isShort and offset >= 65536:
                # offset is now too large - we must convert shorts to longs
                if count != 1:
                    raise RuntimeError("not implemented")  # XXX TODO

                # simple case - the offset is just one and therefore it is
                # local (not referenced with another offset)
                self.rewriteLastShortToLong(offset)
                self.f.seek(-10, SEEK_CUR)
                self.writeShort(4)  # rewrite the type to LONG
                self.f.seek(8, SEEK_CUR)
            elif isShort:
                self.rewriteLastShort(offset)
            else:
                self.rewriteLastLong(offset)

if __name__ == '__main__':
    from PIL import Image
    import os

    testfile = "test.tiff"
    if os.path.exists(testfile):
        os.unlink(testfile)
    with Image.open("multipage.tiff") as ti:
        for idx in range(ti.n_frames):
            ti.seek(idx)
            print ("%i: %s %s" % (idx, repr(ti.size), ti.mode))
            with AppendingTiffWriter(testfile) as tf:
                ti.save(tf)

Could you explain how the test works? Seems that's picking the current number of frames and it's adding them, duplicating the number of frames of the file, isn't it?