How to mask adjustment layers
You can use a mask to apply an adjustment layer selectively so that only specific parts of the layer it’s adjusting are modified.
This can be useful with landscape images, for example, where you may want to darken the sky without changing the brightness of the foreground.
In this case, once you’ve created the adjustment layer, make the adjustment so that the sky looks the way you want and ignore what happens to the foreground.
Then, click the adjustment layer mask thumbnail in the Layers panel and use a black brush to paint over the foreground.
As you paint in the mask the ground will be returned to its original brightness.
Invert the Layer Mask
Painting in a mask to hide the impact of an adjustment layer is a little counterintuitive. Invert the mask by clicking it in the Layers panel and pressing Cmd/Ctrl+I.
This applies the mask to the whole layer. You can then paint in the adjustment using a white brush. If you make a mistake, switch to a black brush and paint the mask back in.
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