Make a pdf look scanned using ImageMagick

scanner.sh

# use ImageMagick convert
# the order is important. the density argument applies to input.pdf and resize and rotate to output.pdf
convert -density 90 input.pdf -rotate 0.5 -attenuate 0.2 +noise Multiplicative -colorspace Gray output.pdf

Nice! The other day, I had 19 pages to sign with unique signatures. First, I used xournal on Ubuntu 20.04 with a stylus, and then I ran the following script:

#!/usr/bin/env bash

# Dependencies
sudo apt install pdftk imagemagick -y

# Output folder
mkdir -p output

# Keep pages in the right order
for i in {1..19}; do
  if (( $i < 10 )); then
    j=0$i
  else
    j=$i
  fi

  pdftk input.pdf cat $i output output/$j.pdf
  convert -density 200 -trim -flatten -quality 80 -attenuate 0.15 +noise Multiplicative -rotate 0.01 output/$j.pdf output/$j.jpg
  convert output/$j.jpg output/$j.pdf
  rm output/$j.jpg
done

pdftk output/* cat output result.pdf

The conversion to .jpg prevents the file from bloating.

The +noise Multiplicative argument created a dappled background behind where I had text but not in other places. Using Gaussian, Laplacian, or Uniform instead of Multiplicative produced better results for me.

If you get this error:

convert-im6.q16: not authorized `input.pdf' @ error/constitute.c/ReadImage/412.
convert-im6.q16: no images defined `output.pdf' @ error/convert.c/ConvertImageCommand/3258.

you can run

sudo mv /etc/ImageMagick-6/policy.xml /etc/ImageMagick-6/policy.xml.off

to disable the policy. When done, you can restore the original with

sudo mv /etc/ImageMagick-6/policy.xml.off /etc/ImageMagick-6/policy.xml

Taken from here

Guys - completely newbie here
I downloaded Visual studio and Git as per install-windows.txt
then ... how do I run the scanner.sh file?
Do I add this file into folder somewhere...?

tks .....

I've improved upon this script slightly (having used it for a while now):

• by splitting the PDF into separate pages per file
• applying slightly different rotations to each page
• recombining the files
• support for macOS automator quick actions
• Fixing the noise so it appears across the document

See: https://gist.github.com/Pezmc/38017cb03daccb17d3835280c568dc0f

Thanks @Pezmc. To have the noise only at the edges instead of across the whole document is a feature IMO, and also keeps the file size much smaller. Unfortunately, I couldn't figure out how to get your script to use noise only at the edges.

I ended up modifyng the original script using the higher density to make the output sharper. Got to keep up with the increasing quality of the scanners in the 3 years since then. 😉

convert -density 130 input.pdf -rotate 0.2 -attenuate 0.2 +noise Multiplicative -colorspace Gray output.pdf

For those on Windows make sure to install Ghostscript as well or else you'll get errors like

convert: FailedToExecuteCommand `"gswin32c.exe" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r150x150"  "-sOutputFile=C:/Users/TURKEY~1/AppData/Local/Temp/magick-9420wtSmlrXSBcfh%d" "-fC:/Users/TURKEY~1/AppData/Local/Temp/magick-9420IJ2RKxHzcTQf" "-fC:/Users/TURKEY~1/AppData/Local/Temp/magick-9420t7VINjcK97Pq"' (The system cannot find the file specified.
) @ error/delegate.c/ExternalDelegateCommand/475.
convert: PDFDelegateFailed `The system cannot find the file specified.
' @ error/pdf.c/ReadPDFImage/662.

thank you! I have used some of these commands to build https://oakpdf.com which not only applies scanner effect, but also allows to insert an image of signature or draw a signature.
My observations regarding -density parameter: 200 is good enough in most cases, while 300 gives ultimate quality - but the build time get catastrophically slow..

Great

Thank you!
I used zenity to add graphical input and output prompts:
convert -density 150 "$(zenity --file-selection --title="Select Input File" --file-filter=*[PpDdFf])" -rotate "$([ $((RANDOM % 2)) -eq 1 ] && echo -)0.$(($RANDOM % 4 + 5))" -attenuate 0.4 +noise Multiplicative -attenuate 0.03 +noise Multiplicative -sharpen 0x1.0 -colorspace Gray "$(zenity --file-selection --save --title="Select Output File" --filename ".pdf")"

Can also be found here as a .desktop file, so the script can be started from the starter on Linux machines:
https://gist.github.com/fewaltix/c1437171d16671741aafe146751dbf9f

work