How to Selectively Apply a Filter in Photoshop CS6
You don’t need to apply filters to an entire image or an entire layer in Photoshop CS6. You can achieve some of the best effects when you apply a filter to only a portion of an image — say, to an object in the foreground but not on the background. Your choices include the following:
Selections: Make a selection and apply the filter only to that selection. You can use Quick Mask mode to paint a selection. This technique can give you a high degree of control; it even lets you feather the edges of the selection so the filter effect fades out.
Channels: You can store selections as alpha channels (visible in the Channels panel, of course). But you can also choose to apply a filter to only one of the other channels, such as the Red, Green, or Blue channels in an RGB image. By using this technique, you can create a filter effect that’s applied to only one color in an image.
Layer Masks: You can use a layer mask to create a selection where you apply the filter to that selection only. Or you can actually apply the filter to the layer mask itself for a special effect.Credit: ©iStockphoto.com/t-lorien Image #5272702
History Brush: Use the History Brush tool to paint a filter onto a portion of the image. Apply the filter to the entire image. Then in the History panel, select the state just before you applied your filter. Set your source state to the filter state and then paint the part of your image you want filtered. For details on working with the History panel.
An advantage of using a Smart Filter is that it comes equipped with its own layer mask. Therefore you can selectively apply the filter to your layer in varying percentages.