This article is based on legacy software.
Photoshop CS3 allows you to mask selected areas of a layer. Masking gives you the ability to hide, edit, and protect selected areas of an image. Furthermore, masking allows you to blend, merge, and add fade attributes to multiple images within the same project. This document will define the two types of layer masks available in Photoshop CS3, detail the necessary steps to add a mask to a selected area of a layer, and explain how to hide and reveal portions of a layer within another layer.
In Photoshop CS3 there are two types of masks available, the layer mask and the vector mask. Both of these masks are greyscale images; meaning, you should paint areas that you would wish to hide in black, and anything you would want to be partially visible, you should paint using various shades of gray. The lighter the gray, the more transparent the selected area is; white is fully visible. Once you hide part of an image using a mask, you can modify or fully restore it at any time because the mask has just covered up, not deleted, that part of the image. This is one of the distinct advantages of masking.
Layer masks are the most common types of masks used. Layer masks are created by using the Painting Tools, primarily the Brush Tool. The layer masking method will cover a large area of an image quickly. While this method may save time, your masked area is more likely to be imprecise and have uneven edges that are not present with the vector masking method.
Vector masks give a much cleaner and more defined image than a layer mask. Vector masks are created by using the Pen, Shape, or Path Selection Tool. While the edges of the mask are more precise, it takes a little more time and precision to create this mask than is necessary with a layer mask.
Creating a Mask
These steps will explain how to add a mask to your image.
NOTE: Layer masks and vector masks can be applied to the same layer.
Open or create your image(s).
Create the number of appropriate layers for your document.
NOTE: For more information on creating layers see Creating Layers.
Place the image(s) you wish to add masking properties to in their respective layers.
NOTE: Name each individual layer with a meaningful name. This will allow you to identify the contents of the layer more quickly. For more information on naming layers see Renaming Layers.
Select the layer you wish to apply a mask to.
From the bottom of the Layers Palette, click Add Layer Mask.
A white thumbnail will appear in the Layers palette on your selected layer. This thumbnail will display the masking properties you add to this layer.
From the Toolbox, click the Brush Tool if you would like a layer mask.
Click the Pen , Path Selection , or Shape Tool , if you would like a vector mask.
NOTE: Layers masks consist of only white and black; therefore, you can only apply the colors white and black to a layer mask with the tools referred to here. To hide areas of a layer, you will want to apply black to the mask. If later you wish to reveal an area that you have masked, apply white to that area of the mask.
Use your desired tool to designate the areas on the image you would like to hide or mask.
When you are finished, the areas that you have masked will be hidden from view.
Hiding and Revealing Selections
You can use a layer mask to hide or reveal a selected area.
Hiding a Selection
Hiding a selection applies a mask over the selected area; the selection is not visible. The portion of the layer directly beneath the masked layer which corresponds to the selection is now visible. In the Layers palette, the layer which has a hidden selection will display a white thumbnail with the selected area in black. The example below shows a hidden selection along with the Layers palette.
Revealing a Selection
Revealing a selection applies a mask to the area surrounding the selected area; only the selection is visible. The portion of the layer directly beneath the masked layer which corresponds to the area outside of the selection is now visible. In the Layers palette, the layer which has a revealed selection will display a black thumbnail with the selected area in white. The example below shows a selection revealed along with the Layers palette.
To hide or reveal a selection:
Select the layer which you wish to apply a mask to.
NOTE: Any layers above the layer you have selected in the Layers palette will not be effected by the mask.
Using a selection tool, select the portion of the image you wish to hide or reveal.
From the Layer menu select Layer Mask » Hide Selection or Reveal Selection.
Your mask is applied accordingly.