Photoshop Tip: Filters are greyed out?
Tips & Tutorials, by Mark White
November 30, 2012
Here’s a possible solution if you ever see your filters disabled
If you ever experience your filters in Photoshop greyed out, make sure that you’re working in RGB Mode.
It may be the case that your image is in CMYK Mode, which disables many of the filters. Go to Image>Mode and choose RGB, and the filters show appear in full.