Improving the Quality on PDF size reducing of the Preview App on Mac
Having a 1200dpi scanned PDF with a size of 20mb’s, I was looking for a way to shrink it down on Mac. Export feature on Preview app was my first option so I tried it by clicking File > Export menu and then selecting the Quartz Filter as Reduce File Size.
The result was total crap. The file size reduced to 40kb from 20mb. The resoultion is way below than expected, probably around 30 or 40 dpi.
So while looking around to resolve this I found out that the reduce file size option could be configured by the file: /System/Library/Filters/Reduce File Size.qfilter.
The qfilter file is just an XML file and the key values Compression Quality (default value 0) and ImageSizeMax (default value 512) should be set bigger values to have better reducing quality. You can select the values according to the dpi value that you want to get. Table is ordered as dpi, compression quality, imagesizemax.