path: root/graphics/img2pdf/README

img2pdf

Lossless conversion of raster images to PDF. You should use img2pdf if
your priorities are (in this order):

    always lossless: the image embedded in the PDF will always have the
exact same color information for every pixel as the input small: if
possible, the difference in filesize between the input image and the
output PDF will only be the overhead of the PDF container itself fast:
if possible, the input image is just pasted into the PDF document as-is
without any CPU hungry re-encoding of the pixel data

Conventional conversion software (like ImageMagick) would either:

    not be lossless because lossy re-encoding to JPEG not be small
because using wasteful flate encoding of raw pixel data not be fast
because input data gets re-encoded

Another advantage of not having to re-encode the input (in most common
situations) is, that img2pdf is able to handle much larger input than
other software, because the raw pixel data never has to be loaded into
memory.

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 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 copied and not re-encoded,
img2pdf is also typically faster than other 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 CMYK input no filter is applied before finally
applying flate compression.  Usage

The images must be provided as files because img2pdf needs to seek in
the file descriptor.

If no output file is specified with the -o/--output option, output will
be done to stdout. A typical invocation is:

$ img2pdf img1.png img2.jpg -o out.pdf

The detailed documentation can be accessed by running:

$ img2pdf --help

Bugs

    If you find a JPEG, JPEG2000, PNG or CCITT Group 4 encoded TIFF file
that, when embedded into the PDF cannot be read by the Adobe Acrobat
Reader, please contact me.

    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 explicitly specify it
using the --colorspace option.

    Input images with alpha channels are not allowed. PDF only supports
transparency using binary masks but is unable to store 8-bit
transparency information as part of the image itself. But img2pdf will
always be lossless and thus, input images must not carry transparency
information.

    img2pdf uses PIL (or Pillow) to obtain image meta data and to
convert the input if necessary. To prevent decompression bomb denial of
service attacks, Pillow limits the maximum number of pixels an input
image is allowed to have. If you are sure that you know what you are
doing, then you can disable this safeguard by passing the
--pillow-limit-break option to img2pdf. This allows one to process even
very large input images.

Installation

On a Debian- and Ubuntu-based systems, img2pdf can be installed from the
official repositories:

$ apt install img2pdf

If you want to install it using pip, you can run:

$ pip3 install img2pdf

If you prefer to install from source code use:

$ cd img2pdf/ $ pip3 install .

To test the console script without installing the package on your
system, use virtualenv:

$ cd img2pdf/ $ virtualenv ve $ ve/bin/pip3 install .

You can then test the converter using:

$ ve/bin/img2pdf -o test.pdf src/tests/test.jpg

For Microsoft Windows users, PyInstaller based .exe files are produced
by appveyor. If you don't want to install Python before using img2pdf
you can head to appveyor and click on "Artifacts" to download the latest
version: https://ci.appveyor.com/project/josch/img2pdf GUI

There exists an experimental GUI with all settings currently disabled.
You can directly convert images to PDF but you cannot set any options
via the GUI yet. If you are interested in adding more features to the
PDF, please submit a merge request. The GUI is based on tkinter and
works on Linux, Windows and MacOS.

Library

The package can also be used as a library:

import img2pdf

# opening from filename with open("name.pdf","wb") as f:
f.write(img2pdf.convert('test.jpg'))

# opening from file handle with open("name.pdf","wb") as f1,
open("test.jpg") as f2: f1.write(img2pdf.convert(f2))

# using in-memory image data with open("name.pdf","wb") as f:
f.write(img2pdf.convert("\x89PNG...")

# multiple inputs (variant 1) with open("name.pdf","wb") as f:
f.write(img2pdf.convert("test1.jpg", "test2.png"))

# multiple inputs (variant 2) with open("name.pdf","wb") as f:
f.write(img2pdf.convert(["test1.jpg", "test2.png"]))

# convert all files ending in .jpg inside a directory dirname =
"/path/to/images" with open("name.pdf","wb") as f: imgs = [] for fname
in os.listdir(dirname): if not fname.endswith(".jpg"): continue path =
os.path.join(dirname, fname) if os.path.isdir(path): continue
imgs.append(path) f.write(img2pdf.convert(imgs))

# convert all files ending in .jpg in a directory and its subdirectories
dirname = "/path/to/images" with open("name.pdf","wb") as f: imgs = []
for r, _, f in os.walk(dirname): for fname in f: if not
fname.endswith(".jpg"): continue imgs.append(os.path.join(r, fname))
f.write(img2pdf.convert(imgs))


# convert all files matching a glob import glob with
open("name.pdf","wb") as f:
f.write(img2pdf.convert(glob.glob("/path/to/*.jpg")))

# writing to file descriptor with open("name.pdf","wb") as f1,
open("test.jpg") as f2: img2pdf.convert(f2, outputstream=f1)

# specify paper size (A4) a4inpt =
(img2pdf.mm_to_pt(210),img2pdf.mm_to_pt(297)) layout_fun =
img2pdf.get_layout_fun(a4inpt) with open("name.pdf","wb") as f:
f.write(img2pdf.convert('test.jpg', layout_fun=layout_fun))

Comparison to ImageMagick

Create a large test image:

$ convert logo: -resize 8000x original.jpg

Convert it into PDF using ImageMagick and img2pdf:

$ time img2pdf original.jpg -o img2pdf.pdf $ time convert original.jpg
imagemagick.pdf

Notice how ImageMagick took an order of magnitude longer to do the
conversion than img2pdf. It also used twice the memory.

Now extract the image data from both PDF documents and compare it to the
original:

$ pdfimages -all img2pdf.pdf tmp $ compare -metric AE original.jpg
tmp-000.jpg null: 0 $ pdfimages -all imagemagick.pdf tmp $ compare
-metric AE original.jpg tmp-000.jpg null: 118716

To get lossless output with ImageMagick we can use Zip compression but
that unnecessarily increases the size of the output:

$ convert original.jpg -compress Zip imagemagick.pdf $ pdfimages -all
imagemagick.pdf tmp $ compare -metric AE original.jpg tmp-000.png null:
0 $ stat --format="%s %n" original.jpg img2pdf.pdf imagemagick.pdf
1535837 original.jpg 1536683 img2pdf.pdf 9397809 imagemagick.pdf

Comparison to pdfLaTeX

pdfLaTeX performs a lossless conversion from included images to PDF by
default. If the input is a JPEG, then it simply embeds the JPEG into the
PDF in the same way as img2pdf does it. But for other image formats it
uses flate compression of the plain pixel data and thus needlessly
increases the output file size:

$ convert logo: -resize 8000x original.png $ cat << END > pdflatex.tex
\documentclass{article} \usepackage{graphicx} \begin{document}
\includegraphics{original.png} \end{document} END $ pdflatex
pdflatex.tex $ stat --format="%s %n" original.png pdflatex.pdf 4500182
original.png 9318120 pdflatex.pdf

Comparison to podofoimg2pdf

Like pdfLaTeX, podofoimg2pdf is able to perform a lossless conversion
from JPEG to PDF by plainly embedding the JPEG data into the pdf
container. But just like pdfLaTeX it uses flate compression for all
other file formats, thus sometimes resulting in larger files than
necessary.

$ convert logo: -resize 8000x original.png $ podofoimg2pdf out.pdf
original.png stat --format="%s %n" original.png out.pdf 4500181
original.png 9335629 out.pdf

It also only supports JPEG, PNG and TIF as input and lacks many of the
convenience features of img2pdf like page sizes, borders, rotation and
metadata.  Comparison to Tesseract OCR

Tesseract OCR comes closest to the functionality img2pdf provides. It is
able to convert JPEG and PNG input to PDF without needlessly increasing
the filesize and is at the same time lossless. So if your input is JPEG
and PNG images, then you should safely be able to use Tesseract instead
of img2pdf. For other input, Tesseract might not do a lossless
conversion. For example it converts CMYK input to RGB and removes the
alpha channel from images with transparency. For multipage TIFF or
animated GIF, it will only convert the first frame.