Robot Tip #4

If your document is in Grayscale mode some filters will be grayed out since those filters are only available in RGB mode. The solution is simple: switch to RGB. apply the filter and then switch back to Grayscale (depending on the filter, some color may be introduced so you may want to first add a Black & White Adjustment layer to control how the color is converted, and then switch the mode back to Grayscale).

(This tip appears thanks to the option in Blogger to schedule posts ahead of time)