Converting a PDF to PNG

Question

I'm trying to convert a PDF to a PNG image (at least the cover of one). I'm successfully extracting the first page of the PDF with pdftk. I'm using imagemagick to do the conversion:

convert cover.pdf cover.png 

This works, but unfortunately the cover.png comes through incorrectly rendered (some of the alpha object in the PDF aren't rendered properly). I know ImageMagick uses GhostScript to do the conversion and if I do it directly with gs I can get the desired results, but I'd rather use the convert library as it has other tools I'd like to leverage.

This command in GhostScript accomplishes the desired image:

gs -sDEVICE=pngalpha -sOutputFile=cover.png -r144 cover.pdf 

I'm wondering is there any way to pass arguments through convert to GhostScript or am I stuck with calling GhostScript directly?

Answer 1

You can use one commandline with two commands (gs, convert) connected through a pipe, if the first command can write its output to stdout, and if the second one can read its input from stdin.

1. Luckily, gs can write to stdout (... -o %stdout ...).
2. Luckily, convert can read from stdin (convert -background transparent - output.png).

Problem solved:

• GS used for alpha channel handling a special image,
• convert used for creating transparent background,
• pipe used to avoid writing out a temp file on disk.

Complete solution:

gs -sDEVICE=pngalpha       \    -o %stdout              \    -r144 cover.pdf         \    |                       \ convert                    \    -background transparent \    -                       \     cover.png 

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Update

If you want to have a separate PNG per PDF page, you can use the %d syntax:

gs -sDEVICE=pngalpha -o file-%03d.png -r144 cover.pdf 

This will create PNG files named page-000.png, page-001.png, ... (Note that the %d-counting is zero-based -- file-000.png corresponds to page 1 of the PDF, 001 to page 2...

Or, if you want to keep your transparent background, for a 100-page PDF, do

for i in {1..100}; do        \                              \   gs -sDEVICE=pngalpha       \      -dFirstPage="${i}"      \      -dLastPage="${i}"       \      -o %stdout              \      -r144 input.pdf         \      |                       \   convert                    \      -background transparent \      -                       \       page-${i}.png ;        \                              \ done 

Answer 2

Out of all the available alternatives I found Inkscape to produce the most accurate results when converting PDFs to PNG. Especially when the source file had transparent layers, Inkscape succeeded where Imagemagick and other tools failed.

This is the command I use:

inkscape "$pdf" -z --export-dpi=600 --export-area-drawing --export-png="$pngfile" 

And here it is implemented in a script:

#!/bin/bash  while [ $# -gt 0 ]; do  pdf=$1 echo "Converting "$pdf" ..." pngfile=`echo "$pdf" | sed 's/\.\w*$/.png/'` inkscape "$pdf" -z --export-dpi=600 --export-area-drawing --export-png="$pngfile" echo "Converted to "$pngfile"" shift  done  echo "All jobs done. Exiting."