This command removes the Alpha channel of the active layer, keeping the Apha channels of the other layers.
If the active layer is the background layer and if you have not added an Alpha channel before (then the layer name is in bold letters in the Layer Dialog), the command is grayed out, inactive.
If the active layer is not the background layer, transparency is replaced with the background color of the Toolbox.
You can access this command from the image menubar through
→ → .In addition, at the Layer Dialog, you can access it through of its context pop-up menu.