| hi cj max,
there's lots of ways to feather, or to simulate it. but, the best way would probably depend on your two images. so, without an image to see, it's a bit hard to say exactly.
nonetheless, you can feather with the smudge or push tool, clone the two sides together, erase with a low opacity and fill, make a new blank raster layer and paint a blending in, airbrush a feather, and probably some others i'm not thinking of currently.
so, take your choice. if you care to post the image, i'm sure someone can give you more exact advice.
Craig |