Lighten those pages
- convert output.pdf -function polynomial 1,0,0,0 darkened.pdf
- mogrify output.pdf -contrast-stretch 2%x20% music1C.pdf
- convert -density 600 output.pdf output-%02d.jpg
(using rm to add security permissions then remove them after https://stackoverflow.com/questions/52861946/imagemagick-not-authorized-to-convert-pdf-to-an-image)
sudo mv /etc/ImageMagick-6/policy.xml /etc/ImageMagick-6/policy.xml.off
-----When done, you can restore the original with
sudo mv /etc/ImageMagick-6/policy.xml.off /etc/ImageMagick-6/policy.xml
3 step process:
- convert your_pdf_filename.pdf output-%02d.jpg
- convert output*.jpg -level 25% final-%02d.jpg
- convert final*.jpg very_readable.pdf
(change the level value)
With the arg -threshold you get a "black and white" (only) image. But I want to keep the gray scale, which is possible with the arg -level: you keep the gray, letting the image with a darker or lighter gray scale. (referring to something like <<< convert output*.jpg -normalize -threshold 80% final-%02d.jpg >>>