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Blending Images with Layer Masks
Layer masks make areas of an image appear transparent by painting with black. Then just as quickly, you can make those areas reappear by painting with white. There are obvious applications to the use of layer maskschanging a sky, removing a tree, or even removing a person who was cut off in the photo. For example, you have an image, and you want the image to change from line art to a normal photograph. To accomplish this, you'll need a copy of the image in a separate layer, a layer mask, and the linear gradient tool.
Blend Images with Layer Masks
Open a document.
Select the layer you want to use for the effect in the Layers palette. If this is a multi-layered document, this layer should be at the top of the layer stack.
Drag the layer over the Create New Layer button to make a copy.TIMESAVER
If making a copy of a layer is a common practice, press Ctrl+J (Win) or
+J (Mac). 
Click the Add Layer Mask button, and then add a layer mask to the copy layer.
Use any of Photoshop's adjust-ment or filter effects to make changes to the copy.
Select black and white for the default foreground and background colors.
Select the Gradient tool, and then select a linear gradient using the foreground to background gradient option.
Click the layer mask thumbnail in the copy layer.
Drag the Gradient tool, left to right, across the document.The image slowly goes transparent from left to right, exposing the original image.[View full size image]
[View full size image]
