Increase the Contrast of a PDF to Sharpen & Darken Text
With Preview you can adjust the contrast of a PDF, this makes the text sharper and darker, and for scanned files or dubious quality PDF’s this makes them significantly easier to read.
The process of increasing contrast and sharpening text in a PDF is made quite simple with Preview app on the Mac, we’ll walk through how to accomplish this.
How to Increase Contrast & Sharpen Text in PDF Files on Mac
This works with all versions of Preview in all versions of Mac OS:
- Open the PDF file with Preview
- From the ‘File’ menu, choose “Export”
- Click on the “Quartz Filter” drop-down menu and choose “Lightness Decrease”
- Choose “Save”
Essentially what you’re doing is re-saving the PDF file with the contrast filter applied, which has the effect of making the text darker and sharper. The exported PDF file will be a new document, leaving the original file untouched. The image below gives a
You may notice re-saving and exporting the file takes a while, this is because Preview is quite literally applying a filter to each individual page of the PDF you are saving. For small PDF files this is quick, for longer PDF files it can take a bit. Just wait before reviewing the changed document.
For a very practical example, I noticed this was needed after downloading the excellent Guy Kawasaki freely available “The Macintosh Way” book, which is a great look at early Apple history. Unfortunately the PDF file text is very light making it difficult to read on some screens, but the Quartz Filter mentioned above greatly helps this.
One potential downside you may notice with some files is an increase in noise. That noise is most noticeable on older PDF’s of scanned books or documents, and at times the trade-off may not be worth it. For the most part it works great though and it improves the readability, contrast, and text sharpness of a document.