I am looking for an automator workflow that reduces the size of multipage pdfs automatically without reducing the visual quality of the contents. I have tried using the standard automator quartz filter and the visual quality was not good. Has anybody been able to do this?
Are you creating the PDFs yourself? If so you might have options at the source.
If they are heavy on images, or is it all text? Do you need colour or would B&W/grey scale suffice?
Often when you are applying compression approaches to a file it is all about choosing the right algorithm for the right types of data and then tuning the parameters to what you find acceptable.
An assortment of Quartz filters for reducing the size of PDFs are available for download at joshcarr/Apple-Quartz-Filters. Included are:
Reduce to 075 dpi average quality
Reduce to 075 dpi low quality
Reduce to 110 dpi average quality
Reduce to 150 dpi average quality - STANDARD COMPRESSION
Reduce to 150 dpi low quality
Reduce to 300 dpi average quality
Reduce to 300 dpi low quality
Reduce to 600 dpi average quality
Reduce to 600 dpi low quality
Just download the zip file, unzip, and follow the instructions on the download page to install the filters.
As @sylumer mentioned, getting to an acceptable combination of file size and quality is often a hit-or-miss affair. One would think that applying a black-and-white filter would decrease the size of a PDF, but sometimes this filter inflates the size. So, you’ll need to experiment, which makes automating the process troublesome; maybe your workflow could apply multiple filters and save the results in a folder somewhere for you to review and select the best result.