100. Mask an Adjustment or Fill Layer Before You Begin  91 About Layers and the Layers Palette
93 Create a Layer Filled with a Color, Gradient, or Pattern 94 Create an Adjustment Layer
See Also  116 Paint an Area of a Photo with a Brush
Unless you made a selection when you created an adjustment or fill layer, the layer initially "flows through" to the layers below, affecting all of them. That's because the mask for the layer (the thing that controls what portions of the layers below are affected) is all white. White on a mask tells you that the pixels on layers below are being filled by a color, pattern, or gradient, or are being affected by the adjustment. You might decide after inserting an adjustment or fill layer that you do not want its effect to be applied to your entire image. For example, if you created an adjustment layer and selected the Brightness and Contrast adjustment, you might want to apply the adjustment to just your subject and not the entire image layer below. To prevent adjustment and fill layers from affecting areas of an image, you must edit the mask for that layerbasically painting parts of the mask black, which causes the mask to block the effect in that area of the layers below. You can use any painting tool to accomplish this, such as the Brush, Pencil, or Paint Bucket. You can also apply a black-to-white gradient, for example, to fade the effect in one direction. You can apply any filter or effect that works on grayscale images, and use the Text or Shape tools to draw the area you want to block. If you use gray, the effects of the adjustment or fill layer are only partially blocked. KEY TERM  | Mask The part of an adjustment or fill layer that acts as a filter, blocking the adjustment or fill from affecting the other layers that lie beneath it in the layer stack. |
You can paint on the mask whether or not it's displayed in the image window; the thumbnail for the mask always appears next to the fill or adjustment layer on the Layers palette. However, for the most part, painting on the mask with it showing in the image window is the best way to go. 1. | Select Layer
Open an image in the Editor in Standard Edit mode and save it in Photoshop (*.psd) format. In the Layers palette, select the adjustment or fill layer whose mask you want to edit.
| 2. | Display the Mask
Press Alt, and on the Layers palette, click the mask thumbnail for the adjustment or fill layer (the thumbnail on the right) to display the mask for that layer in the image window. If you haven't edited the mask, the entire mask layer will be white (indicating that the adjustment or fill layer is affecting all the pixels on the layers below it in the layer stack).
TIPS  | You can copy data into the mask (as long as the mask is displayed), and use that data as your mask. For example, you could select a portion of your image or another image, and paste that onto the mask. The data appears in grayscale; the black pixels (represented by the darkest parts of the image you pasted) block the fill or adjustment layer, and the lighter gray pixels only partially block it. If you need to reposition the mask on the fill or adjustment layer, you must unlink it first by clicking the link icon (the chain), located between the layer thumbnail and the mask thumbnail. Use the Move tool to reposition the mask, and then click the link icon again to re-link the mask to the fill/adjustment layer. |
| 3. | Edit Mask
Click one of the painting tools in the Toolbox, set the foreground color to black, and paint on the mask in the area where you want to block the layer's effect. Paint with gray to partially block the layer's effects. Paint with white again to let the layer's effects flow through.
You can use any tool, filter, effect, or command that works with grayscale images to edit the mask, such as the Gradient tool, Text tool, Shape tool, Paint Bucket tool, Brightness/Contrast or Levels command, or Posterize filter.
| 4. | Hide Mask Again
To view the image again and hide the mask, press Alt and click the mask thumbnail on the Layers palette. Notice that the mask thumbnail has been updated to reflect your changes to the mask.
| 5. | View the Result
When you're satisfied with the image, save the PSD file. Then merge the layers together (if any) and resave the result in JPEG or TIFF format, leaving your PSD image unflattened so that you can return at a later time and make different adjustments if you want.
In this example, I first applied a Levels adjustment to improve the contrast in my niece and great-nephew's face. But I didn't like what it did to the backgroundmade it too bright and distracting. So, I displayed the mask and copied the image layer onto the mask to act as a guide as I painted the background black (to stop the adjustment layer's effect) and painted my subjects white (to let the Levels adjustment affect only that area). The result is a subtle yet striking difference.
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TIP | You can temporarily turn off a mask (and let the fill or adjustment flow through freely) by pressing Shift and clicking the mask thumbnail for the adjustment/fill layer on the Layers palette. |
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