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Add support for JBIG2 (generic coding)

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Implements the proposal detailed at
https://gitlab.mister-muffin.de/josch/img2pdf/issues/112#issuecomment-1304

This is a limited implementation of JBIG2, which can be extended to
support multiple pages, symbol tables, and other features of the format
in the future.

Added a test case based on mono.tif.

Updated the README.md based on
https://gitlab.mister-muffin.de/josch/img2pdf/pulls/184/files#issuecomment-1334
This commit is contained in:
ooBJ3u 2024-09-25 00:00:00 +00:00
parent 819b366bf5
commit e2369eb59a
5 changed files with 110 additions and 20 deletions
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16
README.md
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@ -28,17 +28,19 @@ The following table shows how img2pdf handles different input depending on the
input file format and image color space.
| Format | Colorspace | Result |
| ------------------------------------- | ------------------------------ | ------------- |
| ------------------------------------- | ------------------------------------ | ------------- |
| JPEG | any | direct |
| JPEG2000 | any | direct |
| PNG (non-interlaced, no transparency) | any | direct |
| TIFF (CCITT Group 4) | monochrome | direct |
| any | any except CMYK and monochrome | PNG Paeth |
| any | monochrome | CCITT Group 4 |
| TIFF (CCITT Group 4) | 1-bit monochrome | direct |
| JBIG2 (single-page generic coding) | 1-bit monochrome | direct |
| any | any except CMYK and 1-bit monochrome | PNG Paeth |
| any | 1-bit monochrome | CCITT Group 4 |
| any | CMYK | flate |
For JPEG, JPEG2000, non-interlaced PNG and TIFF images with CCITT Group 4
encoded data, img2pdf directly embeds the image data into the PDF without
For JPEG, JPEG2000, non-interlaced PNG, TIFF images with CCITT Group 4
encoded data, and JBIG2 with single-page generic coding (e.g. using `jbig2enc`),
img2pdf directly embeds the image data into the PDF without
re-encoding it. It thus treats the PDF format merely as a container format for
the image data. In these cases, img2pdf only increases the filesize by the size
of the PDF container (typically around 500 to 700 bytes). Since data is only
@ -47,7 +49,7 @@ solutions for these input formats.
For all other input types, img2pdf first has to transform the pixel data to
make it compatible with PDF. In most cases, the PNG Paeth filter is applied to
the pixel data. For monochrome input, CCITT Group 4 is used instead. Only for
the pixel data. For 1-bit monochrome input, CCITT Group 4 is used instead. Only for
CMYK input no filter is applied before finally applying flate compression.
Usage

92
src/img2pdf.py
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@ -128,7 +128,7 @@ PageOrientation = Enum("PageOrientation", "portrait landscape")
Colorspace = Enum("Colorspace", "RGB RGBA L LA 1 CMYK CMYK;I P PA other")
ImageFormat = Enum(
"ImageFormat", "JPEG JPEG2000 CCITTGroup4 PNG GIF TIFF MPO MIFF other"
"ImageFormat", "JPEG JPEG2000 CCITTGroup4 PNG GIF TIFF MPO MIFF JBIG2 other"
)
PageMode = Enum("PageMode", "none outlines thumbs")
@ -918,6 +918,11 @@ class pdfdoc(object):
self.output_version = "1.5" # jpeg2000 needs pdf 1.5
elif imgformat is ImageFormat.CCITTGroup4:
ofilter = [PdfName.CCITTFaxDecode]
elif imgformat is ImageFormat.JBIG2:
ofilter = PdfName.JBIG2Decode
# JBIG2Decode requires PDF 1.4
if self.output_version < "1.4":
self.output_version = "1.4"
else:
ofilter = PdfName.FlateDecode
@ -1308,6 +1313,25 @@ def get_imgmetadata(
if vdpi is None:
vdpi = default_dpi
ndpi = (hdpi, vdpi)
elif imgformat == ImageFormat.JBIG2:
imgwidthpx, imgheightpx, xres, yres = struct.unpack('>IIII', rawdata[24:40])
INCH_PER_METER = 39.370079
if xres == 0:
hdpi = default_dpi
elif xres < 1000:
# If xres is very small, it's likely accidentally expressed in dpi instead
# of dpm. See e.g. https://github.com/agl/jbig2enc/issues/86
hdpi = xres
else:
hdpi = int(float(xres) / INCH_PER_METER)
if yres == 0:
vdpi = default_dpi
elif yres < 1000:
vdpi = yres
else:
vdpi = int(float(yres) / INCH_PER_METER)
ndpi = (hdpi, vdpi)
ics = "1"
else:
imgwidthpx, imgheightpx = imgdata.size
@ -1334,7 +1358,7 @@ def get_imgmetadata(
# GIF and PNG files with transparency are supported
if imgformat in [ImageFormat.PNG, ImageFormat.GIF, ImageFormat.JPEG2000] and (
ics in ["RGBA", "LA"] or "transparency" in imgdata.info
ics in ["RGBA", "LA"] or (imgdata is not None and "transparency" in imgdata.info)
):
# Must check the IHDR chunk for the bit depth, because PIL would lossily
# convert 16-bit RGBA/LA images to 8-bit.
@ -1350,7 +1374,7 @@ def get_imgmetadata(
raise AlphaChannelError(
"Refusing to work with multiple >8bit channels."
)
elif ics in ["LA", "PA", "RGBA"] or "transparency" in imgdata.info:
elif ics in ["LA", "PA", "RGBA"] or (imgdata is not None and "transparency" in imgdata.info):
raise AlphaChannelError("This function must not be called on images with alpha")
# Since commit 07a96209597c5e8dfe785c757d7051ce67a980fb or release 4.1.0
@ -1455,7 +1479,7 @@ def get_imgmetadata(
logger.debug("input colorspace = %s", color.name)
iccp = None
if "icc_profile" in imgdata.info:
if imgdata is not None and "icc_profile" in imgdata.info:
iccp = imgdata.info.get("icc_profile")
# GIMP saves bilevel TIFF images and palette PNG images with only black and
# white in the palette with an RGB ICC profile which is useless
@ -1805,8 +1829,6 @@ def parse_miff(data):
results.extend(parse_miff(rest[lenpal + lenimgdata :]))
return results
# fmt: on
def read_images(
rawdata, colorspace, first_frame_only=False, rot=None, include_thumbnails=False
):
@ -1820,7 +1842,41 @@ def read_images(
if rawdata[:12] == b"\x00\x00\x00\x0C\x6A\x50\x20\x20\x0D\x0A\x87\x0A":
# image is jpeg2000
imgformat = ImageFormat.JPEG2000
if rawdata[:14].lower() == b"id=imagemagick":
elif rawdata[:8] == b"\x97\x4a\x42\x32\x0d\x0a\x1a\x0a":
# For now we only support single-page generic coding of JBIG2, for example as generated by
# https://github.com/agl/jbig2enc
#
# In fact, you can pipe an example image `like src/tests/input/mono.png` directly into img2pdf:
# jbig2 src/tests/input/mono.png | img2pdf -o src/tests/output/mono.png.pdf
#
# For this we assume that the first 13 bytes are the JBIG file header describing a document with one page,
# followed by a "page information" segment describing the dimensions of that page.
#
# The following annotated `hexdump -C 042.jb2` shows the first 40 bytes that we inspect directly.
# The first 24 bytes (until "||") have to match exactly, while the following 16 bytes are read by get_imgmetadata.
#
# 97 4a 42 32 0d 0a 1a 0a 01 00 00 00 01 00 00 00
# \_____________________/ | \_________/ \______
# magic-bytes org/unk pages seg-num
#
# 00 30 00 01 00 00 00 13 || 00 00 00 73 00 00 00 30
# _/ | | | \_________/ || \_________/ \_________/
# type refs page seg-size || width-px height-px
#
# 00 00 00 48 00 00 00 48
# \_________/ \_________/
# xres yres
#
# For more information on the data format, see:
# * https://github.com/agl/jbig2enc/blob/ea05019/fcd14492.pdf
# For more information about the generic coding, see:
# * https://github.com/agl/jbig2enc/blob/ea05019/src/jbig2enc.cc#L898
imgformat = ImageFormat.JBIG2
if rawdata[:24] != b"\x97\x4a\x42\x32\x0d\x0a\x1a\x0a\x01\x00\x00\x00\x01\x00\x00\x00\x00\x30\x00\x01\x00\x00\x00\x13":
raise ImageOpenError(
"Unsupported JBIG2 format; only single-page generic coding is supported (e.g. from `jbig2enc`)"
)
elif rawdata[:14].lower() == b"id=imagemagick":
# image is in MIFF format
# this is useful for 16 bit CMYK because PNG cannot do CMYK and thus
# we need PIL but PIL cannot do 16 bit
@ -2066,6 +2122,28 @@ def read_images(
)
]
if imgformat == ImageFormat.JBIG2:
color, ndpi, imgwidthpx, imgheightpx, rotation, iccp = get_imgmetadata(
imgdata, imgformat, default_dpi, colorspace, rawdata, rot
)
streamdata = rawdata[13:] # Strip file header
return [
(
color,
ndpi,
imgformat,
streamdata,
None,
imgwidthpx,
imgheightpx,
[],
False,
1,
rotation,
iccp,
)
]
if imgformat == ImageFormat.MIFF:
return parse_miff(rawdata)

10
src/img2pdf_test.py
View file

@ -6987,6 +6987,11 @@ def test_general(general_input, engine):
assert x.Root.Type == "/Catalog"
assert sorted(x.Root.Pages.keys()) == ["/Count", "/Kids", "/Type"]
assert x.Root.Pages.Type == "/Pages"
if f.endswith(".jb2"):
# PIL doens't support .jb2, so we load the original .png, which
# was converted to the .jb2 using `jbig2enc`.
orig_img = Image.open(f.replace(".jb2", ".png"))
else:
orig_img = Image.open(f)
for pagenum in range(len(x.Root.Pages.Kids)):
# retrieve the original image frame that this page was
@ -6995,6 +7000,8 @@ def test_general(general_input, engine):
cur_page = x.Root.Pages.Kids[pagenum]
ndpi = orig_img.info.get("dpi", (96.0, 96.0))
if ndpi[0] <= 0.001 or ndpi[1] <= 0.001:
ndpi = (96.0, 96.0)
# In python3, the returned dpi value for some tiff images will
# not be an integer but a float. To make the behaviour of
# img2pdf the same between python2 and python3, we convert that
@ -7044,6 +7051,7 @@ def test_general(general_input, engine):
"/JPXDecode",
"/FlateDecode",
pikepdf.Array([pikepdf.Name.CCITTFaxDecode]),
"/JBIG2Decode",
]
# test if the image has correct size
@ -7053,6 +7061,8 @@ def test_general(general_input, engine):
# verbatim into the PDF
if imgprops.Filter in ["/DCTDecode", "/JPXDecode"]:
assert cur_page.Resources.XObject.Im0.read_raw_bytes() == orig_imgdata
elif imgprops.Filter == "/JBIG2Decode":
assert cur_page.Resources.XObject.Im0.read_raw_bytes() == orig_imgdata[13:] # Strip file header
elif imgprops.Filter == pikepdf.Array([pikepdf.Name.CCITTFaxDecode]):
tiff_header = tiff_header_for_ccitt(
int(imgprops.Width), int(imgprops.Height), int(imgprops.Length), 4

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