JpegImagePlugin.py

#
# The Python Imaging Library.
# $Id$
#
# JPEG (JFIF) file handling
#
# See "Digital Compression and Coding of Continuous-Tone Still Images,
# Part 1, Requirements and Guidelines" (CCITT T.81 / ISO 10918-1)
#
# History:
# 1995-09-09 fl   Created
# 1995-09-13 fl   Added full parser
# 1996-03-25 fl   Added hack to use the IJG command line utilities
# 1996-05-05 fl   Workaround Photoshop 2.5 CMYK polarity bug
# 1996-05-28 fl   Added draft support, JFIF version (0.1)
# 1996-12-30 fl   Added encoder options, added progression property (0.2)
# 1997-08-27 fl   Save mode 1 images as BW (0.3)
# 1998-07-12 fl   Added YCbCr to draft and save methods (0.4)
# 1998-10-19 fl   Don't hang on files using 16-bit DQT's (0.4.1)
# 2001-04-16 fl   Extract DPI settings from JFIF files (0.4.2)
# 2002-07-01 fl   Skip pad bytes before markers; identify Exif files (0.4.3)
# 2003-04-25 fl   Added experimental EXIF decoder (0.5)
# 2003-06-06 fl   Added experimental EXIF GPSinfo decoder
# 2003-09-13 fl   Extract COM markers
# 2009-09-06 fl   Added icc_profile support (from Florian Hoech)
# 2009-03-06 fl   Changed CMYK handling; always use Adobe polarity (0.6)
# 2009-03-08 fl   Added subsampling support (from Justin Huff).
#
# Copyright (c) 1997-2003 by Secret Labs AB.
# Copyright (c) 1995-1996 by Fredrik Lundh.
#
# See the README file for information on usage and redistribution.
#

from __future__ import print_function

import array
import struct
import io
import warnings
from . import Image, ImageFile, TiffImagePlugin
from ._binary import i8, o8, i16be as i16
from .JpegPresets import presets
from ._util import isStringType

# __version__ is deprecated and will be removed in a future version. Use
# PIL.__version__ instead.
__version__ = "0.6"


#
# Parser

def Skip(self, marker):
    n = i16(self.fp.read(2))-2
    ImageFile._safe_read(self.fp, n)


def APP(self, marker):
    #
    # Application marker.  Store these in the APP dictionary.
    # Also look for well-known application markers.

    n = i16(self.fp.read(2))-2
    s = ImageFile._safe_read(self.fp, n)

    app = "APP%d" % (marker & 15)

    self.app[app] = s  # compatibility
    self.applist.append((app, s))

    if marker == 0xFFE0 and s[:4] == b"JFIF":
        # extract JFIF information
        self.info["jfif"] = version = i16(s, 5)  # version
        self.info["jfif_version"] = divmod(version, 256)
        # extract JFIF properties
        try:
            jfif_unit = i8(s[7])
            jfif_density = i16(s, 8), i16(s, 10)
        except Exception:
            pass
        else:
            if jfif_unit == 1:
                self.info["dpi"] = jfif_density
            self.info["jfif_unit"] = jfif_unit
            self.info["jfif_density"] = jfif_density
    elif marker == 0xFFE1 and s[:5] == b"Exif\0":
        if "exif" not in self.info:
            # extract Exif information (incomplete)
            self.info["exif"] = s  # FIXME: value will change
    elif marker == 0xFFE2 and s[:5] == b"FPXR\0":
        # extract FlashPix information (incomplete)
        self.info["flashpix"] = s  # FIXME: value will change
    elif marker == 0xFFE2 and s[:12] == b"ICC_PROFILE\0":
        # Since an ICC profile can be larger than the maximum size of
        # a JPEG marker (64K), we need provisions to split it into
        # multiple markers. The format defined by the ICC specifies
        # one or more APP2 markers containing the following data:
        #   Identifying string      ASCII "ICC_PROFILE\0"  (12 bytes)
        #   Marker sequence number  1, 2, etc (1 byte)
        #   Number of markers       Total of APP2's used (1 byte)
        #   Profile data            (remainder of APP2 data)
        # Decoders should use the marker sequence numbers to
        # reassemble the profile, rather than assuming that the APP2
        # markers appear in the correct sequence.
        self.icclist.append(s)
    elif marker == 0xFFEE and s[:5] == b"Adobe":
        self.info["adobe"] = i16(s, 5)
        # extract Adobe custom properties
        try:
            adobe_transform = i8(s[1])
        except Exception:
            pass
        else:
            self.info["adobe_transform"] = adobe_transform
    elif marker == 0xFFE2 and s[:4] == b"MPF\0":
        # extract MPO information
        self.info["mp"] = s[4:]
        # offset is current location minus buffer size
        # plus constant header size
        self.info["mpoffset"] = self.fp.tell() - n + 4

    # If DPI isn't in JPEG header, fetch from EXIF
    if "dpi" not in self.info and "exif" in self.info:
        try:
            exif = self._getexif()
            resolution_unit = exif[0x0128]
            x_resolution = exif[0x011A]
            try:
                dpi = x_resolution[0] / x_resolution[1]
            except TypeError:
                dpi = x_resolution
            if resolution_unit == 3:  # cm
                # 1 dpcm = 2.54 dpi
                dpi *= 2.54
            self.info["dpi"] = dpi, dpi
        except (KeyError, SyntaxError, ZeroDivisionError):
            # SyntaxError for invalid/unreadable exif
            # KeyError for dpi not included
            # ZeroDivisionError for invalid dpi rational value
            self.info["dpi"] = 72, 72


def COM(self, marker):
    #
    # Comment marker.  Store these in the APP dictionary.
    n = i16(self.fp.read(2))-2
    s = ImageFile._safe_read(self.fp, n)

    self.app["COM"] = s  # compatibility
    self.applist.append(("COM", s))


def SOF(self, marker):
    #
    # Start of frame marker.  Defines the size and mode of the
    # image.  JPEG is colour blind, so we use some simple
    # heuristics to map the number of layers to an appropriate
    # mode.  Note that this could be made a bit brighter, by
    # looking for JFIF and Adobe APP markers.

    n = i16(self.fp.read(2))-2
    s = ImageFile._safe_read(self.fp, n)
    self._size = i16(s[3:]), i16(s[1:])

    self.bits = i8(s[0])
    if self.bits != 8:
        raise SyntaxError("cannot handle %d-bit layers" % self.bits)

    self.layers = i8(s[5])
    if self.layers == 1:
        self.mode = "L"
    elif self.layers == 3:
        self.mode = "RGB"
    elif self.layers == 4:
        self.mode = "CMYK"
    else:
        raise SyntaxError("cannot handle %d-layer images" % self.layers)

    if marker in [0xFFC2, 0xFFC6, 0xFFCA, 0xFFCE]:
        self.info["progressive"] = self.info["progression"] = 1

    if self.icclist:
        # fixup icc profile
        self.icclist.sort()  # sort by sequence number
        if i8(self.icclist[0][13]) == len(self.icclist):
            profile = []
            for p in self.icclist:
                profile.append(p[14:])
            icc_profile = b"".join(profile)
        else:
            icc_profile = None  # wrong number of fragments
        self.info["icc_profile"] = icc_profile
        self.icclist = None

    for i in range(6, len(s), 3):
        t = s[i:i+3]
        # 4-tuples: id, vsamp, hsamp, qtable
        self.layer.append((t[0], i8(t[1])//16, i8(t[1]) & 15, i8(t[2])))


def DQT(self, marker):
    #
    # Define quantization table.  Support baseline 8-bit tables
    # only.  Note that there might be more than one table in
    # each marker.

    # FIXME: The quantization tables can be used to estimate the
    # compression quality.

    n = i16(self.fp.read(2))-2
    s = ImageFile._safe_read(self.fp, n)
    while len(s):
        if len(s) < 65:
            raise SyntaxError("bad quantization table marker")
        v = i8(s[0])
        if v//16 == 0:
            self.quantization[v & 15] = array.array("B", s[1:65])
            s = s[65:]
        else:
            return  # FIXME: add code to read 16-bit tables!
            # raise SyntaxError, "bad quantization table element size"


#
# JPEG marker table

MARKER = {
    0xFFC0: ("SOF0", "Baseline DCT", SOF),
    0xFFC1: ("SOF1", "Extended Sequential DCT", SOF),
    0xFFC2: ("SOF2", "Progressive DCT", SOF),
    0xFFC3: ("SOF3", "Spatial lossless", SOF),
    0xFFC4: ("DHT", "Define Huffman table", Skip),
    0xFFC5: ("SOF5", "Differential sequential DCT", SOF),
    0xFFC6: ("SOF6", "Differential progressive DCT", SOF),
    0xFFC7: ("SOF7", "Differential spatial", SOF),
    0xFFC8: ("JPG", "Extension", None),
    0xFFC9: ("SOF9", "Extended sequential DCT (AC)", SOF),
    0xFFCA: ("SOF10", "Progressive DCT (AC)", SOF),
    0xFFCB: ("SOF11", "Spatial lossless DCT (AC)", SOF),
    0xFFCC: ("DAC", "Define arithmetic coding conditioning", Skip),
    0xFFCD: ("SOF13", "Differential sequential DCT (AC)", SOF),
    0xFFCE: ("SOF14", "Differential progressive DCT (AC)", SOF),
    0xFFCF: ("SOF15", "Differential spatial (AC)", SOF),
    0xFFD0: ("RST0", "Restart 0", None),
    0xFFD1: ("RST1", "Restart 1", None),
    0xFFD2: ("RST2", "Restart 2", None),
    0xFFD3: ("RST3", "Restart 3", None),
    0xFFD4: ("RST4", "Restart 4", None),
    0xFFD5: ("RST5", "Restart 5", None),
    0xFFD6: ("RST6", "Restart 6", None),
    0xFFD7: ("RST7", "Restart 7", None),
    0xFFD8: ("SOI", "Start of image", None),
    0xFFD9: ("EOI", "End of image", None),
    0xFFDA: ("SOS", "Start of scan", Skip),
    0xFFDB: ("DQT", "Define quantization table", DQT),
    0xFFDC: ("DNL", "Define number of lines", Skip),
    0xFFDD: ("DRI", "Define restart interval", Skip),
    0xFFDE: ("DHP", "Define hierarchical progression", SOF),
    0xFFDF: ("EXP", "Expand reference component", Skip),
    0xFFE0: ("APP0", "Application segment 0", APP),
    0xFFE1: ("APP1", "Application segment 1", APP),
    0xFFE2: ("APP2", "Application segment 2", APP),
    0xFFE3: ("APP3", "Application segment 3", APP),
    0xFFE4: ("APP4", "Application segment 4", APP),
    0xFFE5: ("APP5", "Application segment 5", APP),
    0xFFE6: ("APP6", "Application segment 6", APP),
    0xFFE7: ("APP7", "Application segment 7", APP),
    0xFFE8: ("APP8", "Application segment 8", APP),
    0xFFE9: ("APP9", "Application segment 9", APP),
    0xFFEA: ("APP10", "Application segment 10", APP),
    0xFFEB: ("APP11", "Application segment 11", APP),
    0xFFEC: ("APP12", "Application segment 12", APP),
    0xFFED: ("APP13", "Application segment 13", APP),
    0xFFEE: ("APP14", "Application segment 14", APP),
    0xFFEF: ("APP15", "Application segment 15", APP),
    0xFFF0: ("JPG0", "Extension 0", None),
    0xFFF1: ("JPG1", "Extension 1", None),
    0xFFF2: ("JPG2", "Extension 2", None),
    0xFFF3: ("JPG3", "Extension 3", None),
    0xFFF4: ("JPG4", "Extension 4", None),
    0xFFF5: ("JPG5", "Extension 5", None),
    0xFFF6: ("JPG6", "Extension 6", None),
    0xFFF7: ("JPG7", "Extension 7", None),
    0xFFF8: ("JPG8", "Extension 8", None),
    0xFFF9: ("JPG9", "Extension 9", None),
    0xFFFA: ("JPG10", "Extension 10", None),
    0xFFFB: ("JPG11", "Extension 11", None),
    0xFFFC: ("JPG12", "Extension 12", None),
    0xFFFD: ("JPG13", "Extension 13", None),
    0xFFFE: ("COM", "Comment", COM)
}


def _accept(prefix):
    return prefix[0:1] == b"\377"


##
# Image plugin for JPEG and JFIF images.

class JpegImageFile(ImageFile.ImageFile):

    format = "JPEG"
    format_description = "JPEG (ISO 10918)"

    def _open(self):

        s = self.fp.read(1)

        if i8(s) != 255:
            raise SyntaxError("not a JPEG file")

        # Create attributes
        self.bits = self.layers = 0

        # JPEG specifics (internal)
        self.layer = []
        self.huffman_dc = {}
        self.huffman_ac = {}
        self.quantization = {}
        self.app = {}  # compatibility
        self.applist = []
        self.icclist = []

        while True:

            i = i8(s)
            if i == 0xFF:
                s = s + self.fp.read(1)
                i = i16(s)
            else:
                # Skip non-0xFF junk
                s = self.fp.read(1)
                continue

            if i in MARKER:
                name, description, handler = MARKER[i]
                if handler is not None:
                    handler(self, i)
                if i == 0xFFDA:  # start of scan
                    rawmode = self.mode
                    if self.mode == "CMYK":
                        rawmode = "CMYK;I"  # assume adobe conventions
                    self.tile = [("jpeg", (0, 0) + self.size, 0,
                                 (rawmode, ""))]
                    # self.__offset = self.fp.tell()
                    break
                s = self.fp.read(1)
            elif i == 0 or i == 0xFFFF:
                # padded marker or junk; move on
                s = b"\xff"
            elif i == 0xFF00:  # Skip extraneous data (escaped 0xFF)
                s = self.fp.read(1)
            else:
                raise SyntaxError("no marker found")

    def load_read(self, read_bytes):
        """
        internal: read more image data
        For premature EOF and LOAD_TRUNCATED_IMAGES adds EOI marker
        so libjpeg can finish decoding
        """
        s = self.fp.read(read_bytes)

        if not s and ImageFile.LOAD_TRUNCATED_IMAGES:
            # Premature EOF.
            # Pretend file is finished adding EOI marker
            return b"\xFF\xD9"

        return s

    def draft(self, mode, size):

        if len(self.tile) != 1:
            return

        # Protect from second call
        if self.decoderconfig:
            return

        d, e, o, a = self.tile[0]
        scale = 0

        if a[0] == "RGB" and mode in ["L", "YCbCr"]:
            self.mode = mode
            a = mode, ""

        if size:
            scale = min(self.size[0] // size[0], self.size[1] // size[1])
            for s in [8, 4, 2, 1]:
                if scale >= s:
                    break
            e = e[0], e[1], (e[2]-e[0]+s-1)//s+e[0], (e[3]-e[1]+s-1)//s+e[1]
            self._size = ((self.size[0]+s-1)//s, (self.size[1]+s-1)//s)
            scale = s

        self.tile = [(d, e, o, a)]
        self.decoderconfig = (scale, 0)

        return self

    def load_djpeg(self):

        # ALTERNATIVE: handle JPEGs via the IJG command line utilities

        import subprocess
        import tempfile
        import os
        f, path = tempfile.mkstemp()
        os.close(f)
        if os.path.exists(self.filename):
            subprocess.check_call(["djpeg", "-outfile", path, self.filename])
        else:
            raise ValueError("Invalid Filename")

        try:
            _im = Image.open(path)
            _im.load()
            self.im = _im.im
        finally:
            try:
                os.unlink(path)
            except OSError:
                pass

        self.mode = self.im.mode
        self._size = self.im.size

        self.tile = []

    def _getexif(self):
        return _getexif(self)

    def _getmp(self):
        return _getmp(self)


def _fixup(value):
    try:
        if len(value) == 1 and not isinstance(value, dict):
            return value[0]
    except Exception:
        pass
    return value


class ExifImageFileDirectory(TiffImagePlugin.ImageFileDirectory_v1):
    """
    Specialization for parsing EXIF data:
    - Remove support for v2 to avoid useless computations
    - custom __setitem__ to supports IFD values
    - values are "fixed up" so that 1-size tuples are expanded
    - custom update() to avoid iterating and expanding non parsed data

    The goal is to use the lazyness of ImageFileDirectory_v1 in _getexif().
    """

    def to_v2(self):
        raise NotImplementedError()

    def _setitem(self, tag, value, legacy_api):
        TiffImagePlugin.ImageFileDirectory_v1._setitem(self, tag, value, legacy_api)
        if legacy_api:
            val = self._tags_v1[tag]
            self._tags_v1[tag] = _fixup(val)

    def __setitem__(self, tag, value):
        if isinstance(value, TiffImagePlugin.ImageFileDirectory_v2):
            self._tags_v1[tag] = value
        else:
            TiffImagePlugin.ImageFileDirectory_v1.__setitem__(self, tag, value)

    def __getitem__(self, tag):
        if tag not in self._tags_v1:  # unpack on the fly
            data = self._tagdata[tag]
            typ = self.tagtype[tag]
            size, handler = self._load_dispatch[typ]
            # We don't support v2
            self._setitem(tag, handler(self, data, True), True)
        val = self._tags_v1[tag]
        # Don't try to convert as tuple, it is undone by the _fixup function
        return val

    def update(self, *args, **kwds):
        if args and isinstance(args[0], TiffImagePlugin.ImageFileDirectory_v2):
            other = args[0]
            # custom update
            self._tags_v1.update(other._tags_v1)
            self._tags_v2.update(other._tags_v2)
            self._tagdata.update(other._tagdata)
            self.tagtype.update(other.tagtype)
        else:
            TiffImagePlugin.ImageFileDirectory_v1.update(self, *args, **kwds)


def _getexif(self):
    # Extract EXIF information.  This method is highly experimental,
    # and is likely to be replaced with something better in a future
    # version.

    # The EXIF record consists of a TIFF file embedded in a JPEG
    # application marker (!).
    try:
        data = self.info["exif"]
    except KeyError:
        return None
    fp = io.BytesIO(data[6:])
    head = fp.read(8)
    # process dictionary
    exif = ExifImageFileDirectory(head)
    fp.seek(exif.next)
    exif.load(fp)
    # get exif extension
    try:
        # exif field 0x8769 is an offset pointer to the location
        # of the nested embedded exif ifd.
        # It should be a long, but may be corrupted.
        fp.seek(exif[0x8769])
    except (KeyError, TypeError):
        pass
    else:
        info = ExifImageFileDirectory(head)
        info.load(fp)
        exif.update(info)
    # get gpsinfo extension
    try:
        # exif field 0x8825 is an offset pointer to the location
        # of the nested embedded gps exif ifd.
        # It should be a long, but may be corrupted.
        fp.seek(exif[0x8825])
    except (KeyError, TypeError):
        pass
    else:
        info = ExifImageFileDirectory(head)
        info.load(fp)
        exif[0x8825] = info

    return exif


def _getmp(self):
    # Extract MP information.  This method was inspired by the "highly
    # experimental" _getexif version that's been in use for years now,
    # itself based on the ImageFileDirectory class in the TIFF plug-in.

    # The MP record essentially consists of a TIFF file embedded in a JPEG
    # application marker.
    try:
        data = self.info["mp"]
    except KeyError:
        return None
    file_contents = io.BytesIO(data)
    head = file_contents.read(8)
    endianness = '>' if head[:4] == b'\x4d\x4d\x00\x2a' else '<'
    # process dictionary
    try:
        info = TiffImagePlugin.ImageFileDirectory_v2(head)
        file_contents.seek(info.next)
        info.load(file_contents)
        mp = dict(info)
    except Exception:
        raise SyntaxError("malformed MP Index (unreadable directory)")
    # 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
    mpentries = []
    try:
        rawmpentries = mp[0xB002]
        for entrynum in range(0, quant):
            unpackedentry = struct.unpack_from(
                '{}LLLHH'.format(endianness), rawmpentries, entrynum * 16)
            labels = ('Attribute', 'Size', 'DataOffset', 'EntryNo1',
                      'EntryNo2')
            mpentry = dict(zip(labels, unpackedentry))
            mpentryattr = {
                'DependentParentImageFlag': bool(mpentry['Attribute'] &
                                                 (1 << 31)),
                'DependentChildImageFlag': bool(mpentry['Attribute'] &
                                                (1 << 30)),
                'RepresentativeImageFlag': bool(mpentry['Attribute'] &
                                                (1 << 29)),
                'Reserved': (mpentry['Attribute'] & (3 << 27)) >> 27,
                'ImageDataFormat': (mpentry['Attribute'] & (7 << 24)) >> 24,
                'MPType': mpentry['Attribute'] & 0x00FFFFFF
            }
            if mpentryattr['ImageDataFormat'] == 0:
                mpentryattr['ImageDataFormat'] = 'JPEG'
            else:
                raise SyntaxError("unsupported picture format in MPO")
            mptypemap = {
                0x000000: 'Undefined',
                0x010001: 'Large Thumbnail (VGA Equivalent)',
                0x010002: 'Large Thumbnail (Full HD Equivalent)',
                0x020001: 'Multi-Frame Image (Panorama)',
                0x020002: 'Multi-Frame Image: (Disparity)',
                0x020003: 'Multi-Frame Image: (Multi-Angle)',
                0x030000: 'Baseline MP Primary Image'
            }
            mpentryattr['MPType'] = mptypemap.get(mpentryattr['MPType'],
                                                  'Unknown')
            mpentry['Attribute'] = mpentryattr
            mpentries.append(mpentry)
        mp[0xB002] = mpentries
    except KeyError:
        raise SyntaxError("malformed MP Index (bad MP Entry)")
    # Next we should try and parse the individual image unique ID list;
    # we don't because I've never seen this actually used in a real MPO
    # file and so can't test it.
    return mp


# --------------------------------------------------------------------
# stuff to save JPEG files

RAWMODE = {
    "1": "L",
    "L": "L",
    "RGB": "RGB",
    "RGBX": "RGB",
    "CMYK": "CMYK;I",  # assume adobe conventions
    "YCbCr": "YCbCr",
}

zigzag_index = (0,  1,  5,  6, 14, 15, 27, 28,  # noqa: E128
                2,  4,  7, 13, 16, 26, 29, 42,
                3,  8, 12, 17, 25, 30, 41, 43,
                9, 11, 18, 24, 31, 40, 44, 53,
               10, 19, 23, 32, 39, 45, 52, 54,
               20, 22, 33, 38, 46, 51, 55, 60,
               21, 34, 37, 47, 50, 56, 59, 61,
               35, 36, 48, 49, 57, 58, 62, 63)

samplings = {(1, 1, 1, 1, 1, 1): 0,
             (2, 1, 1, 1, 1, 1): 1,
             (2, 2, 1, 1, 1, 1): 2,
             }


def convert_dict_qtables(qtables):
    qtables = [qtables[key] for key in range(len(qtables)) if key in qtables]
    for idx, table in enumerate(qtables):
        qtables[idx] = [table[i] for i in zigzag_index]
    return qtables


def get_sampling(im):
    # There's no subsampling when image have only 1 layer
    # (grayscale images) or when they are CMYK (4 layers),
    # so set subsampling to default value.
    #
    # NOTE: currently Pillow can't encode JPEG to YCCK format.
    # If YCCK support is added in the future, subsampling code will have
    # to be updated (here and in JpegEncode.c) to deal with 4 layers.
    if not hasattr(im, 'layers') or im.layers in (1, 4):
        return -1
    sampling = im.layer[0][1:3] + im.layer[1][1:3] + im.layer[2][1:3]
    return samplings.get(sampling, -1)


def _save(im, fp, filename):

    try:
        rawmode = RAWMODE[im.mode]
    except KeyError:
        raise IOError("cannot write mode %s as JPEG" % im.mode)

    info = im.encoderinfo

    dpi = [int(round(x)) for x in info.get("dpi", (0, 0))]

    quality = info.get("quality", 0)
    subsampling = info.get("subsampling", -1)
    qtables = info.get("qtables")

    if quality == "keep":
        quality = 0
        subsampling = "keep"
        qtables = "keep"
    elif quality in presets:
        preset = presets[quality]
        quality = 0
        subsampling = preset.get('subsampling', -1)
        qtables = preset.get('quantization')
    elif not isinstance(quality, int):
        raise ValueError("Invalid quality setting")
    else:
        if subsampling in presets:
            subsampling = presets[subsampling].get('subsampling', -1)
        if isStringType(qtables) and qtables in presets:
            qtables = presets[qtables].get('quantization')

    if subsampling == "4:4:4":
        subsampling = 0
    elif subsampling == "4:2:2":
        subsampling = 1
    elif subsampling == "4:2:0":
        subsampling = 2
    elif subsampling == "4:1:1":
        # For compatibility. Before Pillow 4.3, 4:1:1 actually meant 4:2:0.
        # Set 4:2:0 if someone is still using that value.
        subsampling = 2
    elif subsampling == "keep":
        if im.format != "JPEG":
            raise ValueError(
                "Cannot use 'keep' when original image is not a JPEG")
        subsampling = get_sampling(im)

    def validate_qtables(qtables):
        if qtables is None:
            return qtables
        if isStringType(qtables):
            try:
                lines = [int(num) for line in qtables.splitlines()
                         for num in line.split('#', 1)[0].split()]
            except ValueError:
                raise ValueError("Invalid quantization table")
            else:
                qtables = [lines[s:s+64] for s in range(0, len(lines), 64)]
        if isinstance(qtables, (tuple, list, dict)):
            if isinstance(qtables, dict):
                qtables = convert_dict_qtables(qtables)
            elif isinstance(qtables, tuple):
                qtables = list(qtables)
            if not (0 < len(qtables) < 5):
                raise ValueError("None or too many quantization tables")
            for idx, table in enumerate(qtables):
                try:
                    if len(table) != 64:
                        raise TypeError
                    table = array.array('B', table)
                except TypeError:
                    raise ValueError("Invalid quantization table")
                else:
                    qtables[idx] = list(table)
            return qtables

    if qtables == "keep":
        if im.format != "JPEG":
            raise ValueError(
                "Cannot use 'keep' when original image is not a JPEG")
        qtables = getattr(im, "quantization", None)
    qtables = validate_qtables(qtables)

    extra = b""

    icc_profile = info.get("icc_profile")
    if icc_profile:
        ICC_OVERHEAD_LEN = 14
        MAX_BYTES_IN_MARKER = 65533
        MAX_DATA_BYTES_IN_MARKER = MAX_BYTES_IN_MARKER - ICC_OVERHEAD_LEN
        markers = []
        while icc_profile:
            markers.append(icc_profile[:MAX_DATA_BYTES_IN_MARKER])
            icc_profile = icc_profile[MAX_DATA_BYTES_IN_MARKER:]
        i = 1
        for marker in markers:
            size = struct.pack(">H", 2 + ICC_OVERHEAD_LEN + len(marker))
            extra += (b"\xFF\xE2" + size + b"ICC_PROFILE\0" + o8(i) +
                      o8(len(markers)) + marker)
            i += 1

    # "progressive" is the official name, but older documentation
    # says "progression"
    # FIXME: issue a warning if the wrong form is used (post-1.1.7)
    progressive = (info.get("progressive", False) or
                   info.get("progression", False))

    optimize = info.get("optimize", False)

    # get keyword arguments
    im.encoderconfig = (
        quality,
        progressive,
        info.get("smooth", 0),
        optimize,
        info.get("streamtype", 0),
        dpi[0], dpi[1],
        subsampling,
        qtables,
        extra,
        info.get("exif", b"")
        )

    # if we optimize, libjpeg needs a buffer big enough to hold the whole image
    # in a shot. Guessing on the size, at im.size bytes. (raw pixel size is
    # channels*size, this is a value that's been used in a django patch.
    # https://github.com/matthewwithanm/django-imagekit/issues/50
    bufsize = 0
    if optimize or progressive:
        # CMYK can be bigger
        if im.mode == 'CMYK':
            bufsize = 4 * im.size[0] * im.size[1]
        # keep sets quality to 0, but the actual value may be high.
        elif quality >= 95 or quality == 0:
            bufsize = 2 * im.size[0] * im.size[1]
        else:
            bufsize = im.size[0] * im.size[1]

    # The exif info needs to be written as one block, + APP1, + one spare byte.
    # Ensure that our buffer is big enough. Same with the icc_profile block.
    bufsize = max(ImageFile.MAXBLOCK, bufsize, len(info.get("exif", b"")) + 5,
                  len(extra) + 1)

    ImageFile._save(im, fp, [("jpeg", (0, 0)+im.size, 0, rawmode)], bufsize)


def _save_cjpeg(im, fp, filename):
    # ALTERNATIVE: handle JPEGs via the IJG command line utilities.
    import os
    import subprocess
    tempfile = im._dump()
    subprocess.check_call(["cjpeg", "-outfile", filename, tempfile])
    try:
        os.unlink(tempfile)
    except OSError:
        pass


##
# Factory for making JPEG and MPO instances
def jpeg_factory(fp=None, filename=None):
    im = JpegImageFile(fp, filename)
    try:
        mpheader = im._getmp()
        if mpheader[45057] > 1:
            # It's actually an MPO
            from .MpoImagePlugin import MpoImageFile
            im = MpoImageFile(fp, filename)
    except (TypeError, IndexError):
        # It is really a JPEG
        pass
    except SyntaxError:
        warnings.warn("Image appears to be a malformed MPO file, it will be "
                      "interpreted as a base JPEG file")
    return im


# ---------------------------------------------------------------------
# Registry stuff

Image.register_open(JpegImageFile.format, jpeg_factory, _accept)
Image.register_save(JpegImageFile.format, _save)

Image.register_extensions(JpegImageFile.format,
                          [".jfif", ".jpe", ".jpg", ".jpeg"])

Image.register_mime(JpegImageFile.format, "image/jpeg")