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== img2pdf ==
Lossless conversion of images to PDF without unnecessarily re-encoding JPEG
files. Thus, no loss of quality and no unnecessary large output file.
PDF is able to embed JPEG images as they are without re-encoding them (and
hence loosing quality) but I was missing a tool to do this automatically, thus
I wrote this piece of python code.
If you know how to embed JPEG images into a PDF container without
recompression, using existing tools, please contact me so that I can put this
code into the garbage bin :D
The program will take image filenames from commandline arguments and output a
PDF file with them embedded into it. If the input image is a JPEG file, it will
be included as-is without any processing. If it is in any other format, the
image will be included as zip-encoded RGB. As a result, this tool will be able
to lossless wrap any image into a PDF container while performing better (in
terms of quality/filesize ratio) than existing tools in case the input image is
a JPEG.
For the record, the imagemagick command to lossless convert any image to
PDF using zip-encoding, is:
convert input.jpg -compress Zip output.pdf
The downside is, that using imagemagick like this will make the resulting PDF
files a few times bigger than the input JPEG and can also not output a
multipage PDF.
img2pdf is able to output a PDF with multiple pages if more than one input
image is given, losslessly embed JPEGs into a PDF container without adding more
overhead than the PDF structure itself and will save all other graphics formats
using lossless zip-compression.
If you find a JPEG that, when embedded can not be read by the Adobe Acrobat
Reader, please contact me.
For lossless conversion of other formats than JPEG, zip/flate encoding is used.
This choice is based on a number of tests I did on images. I converted them
into PDF using imagemagick and all compressions it has to offer and then
compared the output size of the lossless variants. In all my tests, zip/flate
encoding performed best. You can verify my findings using the test_comp.sh
script with any input image given as a commandline argument. If you find an
input file that is outperformed by another lossless compression, contact me.

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#!/usr/bin/env python
import Image
import sys
import zlib
import argparse
from datetime import datetime
def parse(cont, indent=1):
if type(cont) is dict:
return "<<\n"+"\n".join([4*indent*" "+"%s %s"%(k, parse(v, indent+1)) for k, v in cont.items()])+"\n"+4*(indent-1)*" "+">>"
elif type(cont) is int or type(cont) is float:
return str(cont)
elif isinstance(cont, obj):
return "%d 0 R"%cont.get_identifier()
elif type(cont) is str:
return cont
elif type(cont) is list:
return "[ "+" ".join([parse(c, indent) for c in cont])+" ]"
class obj():
def __init__(self, content, stream=None):
self.content = content
self.stream = stream
def tostring(self, identifier):
self.identifier = identifier
if self.stream:
return "%d 0 obj "%identifier+parse(self.content)+"\nstream\n"+self.stream+"\nendstream\nendobj\n"
else:
return "%d 0 obj "%identifier+parse(self.content)+" endobj\n"
def get_identifier(self):
if not hasattr(self, 'identifier'):
raise Exception("no id set yet, call tostring() on obj first")
return self.identifier
def main(images, dpi, title=None, author=None, creator=None, producer=None,
creationdate=None, moddate=None, subject=None, keywords=None):
now = datetime.now()
info = dict()
if title:
info["/Title"] = "("+title+")"
if author:
info["/Author"] = "("+author+")"
if creator:
info["/Creator"] = "("+creator+")"
if producer:
info["/Producer"] = "("+producer+")"
if creationdate:
info["/CreationDate"] = "(D:"+creationdate.strftime("%Y%m%d%H%M%S")+")"
else:
info["/CreationDate"] = "(D:"+now.strftime("%Y%m%d%H%M%S")+")"
if moddate:
info["/ModDate"] = "(D:"+moddate.strftime("%Y%m%d%H%M%S")+")"
else:
info["/ModDate"] = "(D:"+now.strftime("%Y%m%d%H%M%S")+")"
if subject:
info["/Subject"] = "("+subject+")"
if keywords:
info["/Keywords"] = "("+",".join(keywords)+")"
info = obj(info)
pagestuples = list()
for im in images:
imgdata = Image.open(im)
width, height = imgdata.size
if dpi:
dpi_x, dpi_y = dpi, dpi
else:
dpi_x, dpi_y = imgdata.info.get("dpi", (96, 96))
pdf_x, pdf_y = 72.0*width/dpi_x, 72.0*height/dpi_y # pdf units = 1/72 inch
imgformat = imgdata.format
color = imgdata.mode
if color == 'L':
color = "/DeviceGray"
elif color == 'RGB':
color = "/DeviceRGB"
else:
print "unsupported color space:", color
exit(1)
# either embed the whole jpeg or deflate the bitmap representation
if imgformat is "JPEG":
ofilter = [ "/DCTDecode" ]
im.seek(0)
imgdata = im.read()
else:
ofilter = [ "/FlateDecode" ]
imgdata = zlib.compress(imgdata.tostring())
im.close()
image = obj({
"/Type": "/XObject",
"/Subtype": "/Image",
"/Filter": ofilter,
"/Width": width,
"/Height": height,
"/ColorSpace": color,
"/BitsPerComponent": 8, # hardcoded as PIL doesnt provide bits for non-jpeg formats
"/Length": len(imgdata)
}, imgdata)
text = "q\n%f 0 0 %f 0 0 cm\n/Im0 Do\nQ"%(pdf_x, pdf_y)
content = obj({
"/Length": len(text)
}, text)
page = obj({
"/Type": "/Page",
"/Resources": {
"/XObject": {
"/Im0": image
}
},
"/MediaBox": [0, 0, pdf_x, pdf_y],
"/Contents": content
})
pagestuples.append((image, content, page))
pages = obj({
"/Type": "/Pages",
"/Kids": [ pagetuple[2] for pagetuple in pagestuples ],
"/Count": len(pagestuples)
})
catalog = obj({
"/Pages": pages,
"/Type": "/Catalog"
})
objects = list()
objects.append(info.tostring(3*(len(pagestuples)+1)))
for i, (image, content, page) in enumerate(reversed(pagestuples)):
objects.append(image.tostring(3*(len(pagestuples)-i+1)-1))
objects.append(content.tostring(3*(len(pagestuples)-i+1)-2))
objects.append(page.tostring(3*(len(pagestuples)-i+1)-3))
objects.append(pages.tostring(2))
objects.append(catalog.tostring(1))
objects.reverse()
xreftable = list()
result = "%PDF-1.3\n"
xreftable.append("0000000000 65535 f \n")
for o in objects:
xreftable.append("%010d 00000 n \n"%len(result))
result += o
xrefoffset = len(result)
result += "xref\n"
result += "0 %d\n"%len(xreftable)
for x in xreftable:
result += x
result += "trailer\n"
result += parse({"/Size": len(xreftable), "/Info": info, "/Root": catalog})+"\n"
result += "startxref\n"
result += "%d\n"%xrefoffset
result += "%%EOF\n"
return result
if __name__ == "__main__":
parser = argparse.ArgumentParser(description='lossless conversion/embedding of images (in)to pdf')
parser.add_argument('images', metavar='infile', type=argparse.FileType('r'),
nargs='*', default=[sys.stdin], help='input file(s) (default: stdin)')
parser.add_argument('-o', '--output', metavar='out', type=argparse.FileType('w'),
default=sys.stdout, help='output file (default: stdout)')
def positive_float(string):
value = float(string)
if value <= 0:
msg = "%r is not positive"%string
raise argparse.ArgumentTypeError(msg)
return value
parser.add_argument('-d', '--dpi', metavar='dpi', type=positive_float, help='dpi for pdf output (default: 96.0)')
parser.add_argument('-t', '--title', metavar='title', type=str, help='title for metadata')
parser.add_argument('-a', '--author', metavar='author', type=str, help='author for metadata')
parser.add_argument('-c', '--creator', metavar='creator', type=str, help='creator for metadata')
parser.add_argument('-p', '--producer', metavar='producer', type=str, help='producer for metadata')
def valid_date(string):
return datetime.strptime(string, "%Y-%m-%dT%H:%M:%S")
parser.add_argument('-r', '--creationdate', metavar='creationdate',
type=valid_date, help='creation date for metadata in YYYY-MM-DDTHH:MM:SS format')
parser.add_argument('-m', '--moddate', metavar='moddate',
type=valid_date, help='modification date for metadata in YYYY-MM-DDTHH:MM:SS format')
parser.add_argument('-s', '--subject', metavar='subject', type=str, help='subject for metadata')
parser.add_argument('-k', '--keywords', metavar='kw', type=str, nargs='+', help='keywords for metadata')
args = parser.parse_args()
args.output.write(main(args.images, args.dpi, args.title, args.author,
args.creator, args.producer, args.creationdate, args.moddate,
args.subject, args.keywords))