Now and then, you may want to apply an effect to only a portion of an image rather than the entire picture. This can be accomplished using layers and masks. The process is essentially to duplicate the background layer, apply the effect to the duplicate layer, and mask the portion of the image where you don’t want the effect to apply.
In this project you will use Pixelmator‘s tools and effects to add realistic-looking falling snow to an image. I’d like to point out now that most of the settings used in this example are not hard and fast but rather suggested values which you will likely want to modify to get the exact results you want.