Layer Locks & Filtering
At the top of Photoshop’s Layers panel you will find two clusters of icons. The topmost cluster filters layers, allowing you to quickly hide layers, revealing only the ones you need to see. The other locks the active layer(s) in different ways.
These buttons provide a fast way to protect different aspects of layers. Some are more intuitive than others. Hover your cursor over each to see its name.
Lock Transparent Pixels
This lock protects the transparent parts of a layer. If you paint or apply a filter, only the nontransparent pixels are affected. Translucent pixels retain their level of transparency too. In the following illustration, I painted across this layer that contains opaque and translucent pixels.