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img2pdf/README.md

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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.

background

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

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 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.

bugs

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.