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xiota 2015-03-20 11:30:19 -07:00 committed by xiota
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img2pdf
=======
Lossless conversion of images to PDF without unnecessarily re-encoding JPEG and
JPEG2000 files. Thus, no loss of quality and no unnecessary large output file.
Losslessly convert images to PDF without unnecessarily re-encoding JPEG and
JPEG2000 files. Image quality is retained without unnecessarily increasing
file size.
Background
----------
PDF is able to embed JPEG and JPEG2000 images as they are without re-encoding
them (and hence losing quality) but I was missing a tool to do this
automatically, thus I wrote this piece of python code.
Quality loss can be avoided when converting JPEG and JPEG2000 images to
PDF by embedding them without re-encoding. I wrote this piece of python code.
because I was missing a tool to do this automatically.
If you know how to embed JPEG and JPEG2000 images into a PDF container without
recompression, using existing tools, please contact me so that I can put this
@ -18,43 +19,41 @@ code into the garbage bin :D
Functionality
-------------
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 or JPEG2000
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 or JPEG2000 file.
This program will take a list of images and produce a PDF file with the
images embedded in it. JPEG and JPEG2000 images will be included without
recompression. Images in other formats will be included with zip/flate
encoding. As a result, this tool is able to losslessly wrap any image
into a PDF container with a quality-filesize ratio that is typically better
than that of existing tools.
For example, imagemagick will re-encode the input JPEG image and thus change
its content:
For example, imagemagick will re-encode the input JPEG image (thus changing
its content):
$ convert img.jpg img.pdf
$ pdfimages img.pdf img.extr # not using -j to be extra sure there is no recompression
$ compare -metric AE img.jpg img.extr-000.ppm null:
1.6301e+06
If one wants to do a lossless conversion from any format to PDF with
imagemagick then one has to use zip-encoding:
If one wants to losslessly convert from any format to PDF with
imagemagick, one has to use zip compression:
$ convert input.jpg -compress Zip output.pdf
$ pdfimages img.pdf img.extr # not using -j to be extra sure there is no recompression
$ compare -metric AE img.jpg img.extr-000.ppm null:
0
The downside is, that using imagemagick like this will make the resulting PDF
files a few times bigger than the input JPEG or JPEG2000 file and can also not
output a multipage PDF.
However, this approach will result in PDF files that are a few times larger
than the input JPEG or JPEG2000 file.
img2pdf is able to output a PDF with multiple pages if more than one input
image is given, losslessly embed JPEG and JPEG2000 files into a PDF container
without adding more overhead than the PDF structure itself and will save all
other graphics formats using lossless zip-compression.
img2pdf is able to losslessly embed JPEG and JPEG2000 files into a PDF
container without additional overhead (aside from the PDF structure itself),
save other graphics formats using lossless zip compression,
and produce multi-page PDF files when more than one input image is given.
Another nifty advantage: Since no re-encoding is done in case of JPEG images,
the conversion is many (ten to hundred) times faster with img2pdf compared to
imagemagick. While a run of above convert command with a 2.8MB JPEG takes 27
seconds (on average) on my machine, conversion using img2pdf takes just a
Also, since JPEG and JPEG2000 images are not reencoded, conversion with
img2pdf is several (ten to hundred) times faster than with imagemagick.
While the above convert command with a 2.8MB JPEG took 27 seconds
(on average) on my machine, conversion using img2pdf took just a
fraction of a second.
Commandline Arguments
@ -81,27 +80,26 @@ More help is available with the -h or --help option.
Bugs
----
If you find a JPEG or JPEG2000 file that, when embedded can not be read by the
Adobe Acrobat Reader, please contact me.
If you find a JPEG or JPEG2000 file that, when embedded cannot be read
by the Adobe Acrobat Reader, please contact me.
For lossless conversion of other formats than JPEG or JPEG2000 files, 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.
For lossless conversion of formats other than JPEG or JPEG2000, zip/flate
encoding is used. This choice is based on tests I did with a number of images.
I converted them into PDF using the lossless variants of the compression
formats offered by imagemagick. 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 method, contact me.
I have not yet figured out how to read the colorspace from jpeg2000 files.
Therefor jpeg2000 files use DeviceRGB per default. If your jpeg2000 files are
of any other colorspace you must force it using the --colorspace option.
Like -C L for DeviceGray.
I have not yet figured out how to determine the colorspace of JPEG2000 files.
Therefore JPEG2000 files use DeviceRGB by default. For JPEG2000 files with
other colorspaces, you must force it using the `--colorspace` option.
Installation
------------
On a Debian/Ubuntu based OS, the following dependencies are needed:
On a Debian- and Ubuntu-based systems, dependencies may be installed
with the following command:
apt-get install python python-pil python-setuptools
@ -109,17 +107,17 @@ Or for Python 3:
apt-get install python3 python3-pil python3-setuptools
You can install the package using:
You can then install the package using:
$ pip install img2pdf
If you want to install from source code simply use:
If you prefer to install from source code use:
$ cd img2pdf/
$ pip install .
To test the console script without installing the package on your system,
simply use virtualenv:
use virtualenv:
$ cd img2pdf/
$ virtualenv ve
@ -129,7 +127,7 @@ You can then test the converter using:
$ ve/bin/img2pdf -o test.pdf src/tests/test.jpg
Note that the package can also be used as a library as follows:
The package can also be used as a library:
import img2pdf
pdf_bytes = img2pdf.convert(['test.jpg'])