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README.md: Improve wording

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Johannes 'josch' Schauer 2017-01-20 09:43:42 +01:00
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@ -2,19 +2,19 @@ img2pdf
=======
Losslessly convert raster images to PDF. The file size will not unnecessarily
increase. One major application would be a number of scans made in JPEG format
which should now become part of a single PDF document. Existing solutions
would either re-encode the input JPEG files (leading to quality loss) or store
them in the zip/flate format which results into the PDF becoming unnecessarily
large in terms of its file size.
increase. It can for example be used to create a PDF document from a number of
scans that are only available in JPEG format. Existing solutions would either
re-encode the input JPEG files (leading to quality loss) or store them in the
zip/flate format which results into the PDF becoming unnecessarily large in
terms of its file size.
Background
----------
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. Img2pdf basically just
wraps JPEG images into the PDF container as they are.
embedding them into the PDF without re-encoding them. This is what img2pdf
does. It thus treats the PDF format merely as a container format for storing
one or more JPEGs without re-encoding the JPEG images themselves.
If you know an existing tool which allows one to embed JPEG and JPEG2000 images
into a PDF container without recompression, please contact me so that I can put
@ -23,12 +23,18 @@ this code into the garbage bin.
Functionality
-------------
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. Raster images in other formats will be included with zip/flate
encoding which usually leads to an increase in the resulting size because
formats like png compress better than PDF which just zip/flate compresses the
RGB data. As a result, this tool is able to losslessly wrap images into a PDF
This program will take a list of raster images and produce a PDF file with the
images embedded in it. JPEG and JPEG2000 images will be included without
recompression and the resulting PDF will only be slightly larger than the input
images due to the overhead of the PDF container. Raster images in other
formats (like png, gif or tif) will be included using the lossless zip/flate
encoding which usually leads to a significant increase in the PDF size if the
input was for example a png image. This is unfortunately unavoidable because
there is no other way to store arbitrary RGB bitmaps in PDF in a lossless way
other than zip/flate encoding. And zip/flate compresses bitmaps worse than png
is able to compress them.
As a result, this tool is able to losslessly wrap raster images into a PDF
container with a quality to filesize ratio that is typically better (in case of
JPEG and JPEG2000 images) or equal (in case of other formats) than that of
existing tools.
@ -67,7 +73,9 @@ 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.
done to stdout. A typical invocation is:
img2pdf img1.png img2.jpg -o out.pdf
The detailed documentation can be accessed by running: