Adjust PDF Contrast with Adobe Reader/Acrobat?

We get PDF's from our professor to read for homework but they're often scanned documents, is there a way to adjust the contrast of the text to make it easier to read?

Edit: I've got Photoshop but is there a way to do it from a PDF reader?

Edit2: Windows XP, 7 ** Windows or Ubuntu Only **

Solution 1:

You can try this:

Go to Edit>Preferences>Accessibility

This will not change the true contrast, but you can pick contrasting colors of your choice, or one of the defaults, as in the screenshot.

Solution 2:

You could try Imagemagick - it's a graphics manipulation program that can read and write PDFs too.

There are a few command line options that may help - for example: -normalize, -contrast and -contrast-stretch

http://www.imagemagick.org

Try something like: convert original.pdf -contrast new.pdf

More info and examples on the site.

Solution 3:

Under OS X, you can use ColorSync which is installed by default. There are many filters, and one is for decreasing contrast.