Learn how to quickly edit layer masks in 5 simple steps
Masking enables you to create anything you can imagine in Photoshop. You can add a mask to a layer and use the mask to hide portions of the layer and reveal the layers below.
To easily edit and refine existing layer masks, do the following:
Click the Mask thumbnail in the Layers panel.
Select any of the editing or painting tools. The foreground and background colors assume default grayscale values when the mask is active.
(Optional) To edit the layer instead of the layer mask, select it by clicking its thumbnail in the Layers panel. A border appears around the layer thumbnail.
To paste a copied selection into a layer mask, Alt-click (Win) or Option-click (Mac) the layer mask thumbnail in the Layers panel to select and display the mask channel. Choose Edit > Paste and then Select > Deselect. The selection is converted to grayscale and added to the mask. Click the layer thumbnail in the Layers panel to deselect the mask channel.