Home » Tip of The Day » Lock Transparent PixelsLock Transparent Pixels May 21, 2016. Posted in: Tip Of The Day. To lock transparent pixels, so that you can only paint in pixels that are opaque, press the / (forward slash) key or click on the first icon next to the word “Lock:” in the Layers panel. To unlock transparent pixels press the / key again. « Previous Photoshop Tip: | Next Photoshop Tip: » Sign-up for the PTC Newsletter so that you'll never miss a tutorial!. Your Email Address: