>>2121834For something like this, use the magic wand to color select the black background. Invert the mask so only the girl is selected.
Expand the mask 1 pixel and feather it outwards 1 more. The feathering is important because it softens the edge and eliminates jaggies. (The actual numbers may vary with the image you're working on.)
So we have the girl and a dark boarder. Cut them to another layer. Fill the original layer (now just a background) with a contrasting color. This enables you to see flaws easily.
Zoom in and scroll around the boundary. Narrow "crevices", such as I've circled, will show as unwanted material. Use a very tiny eraser to eliminate them. Or use another selection tool to mark them, feather, and erase.
To make this clearer, I duped the background as a new layer and deleted half the contrasting color. Then I took a screenshot. This lets you see the "transparency grid" -- though it degraded the image. The original edge was smoother than what you see here.
Experiment. If you find you still have an unwanted light "halo", select the girl again (easy since she's on her own layer), feather inside a pixel, invert and erase. That wipes out the halo. Of course, you can wipe out only selected parts as well. You can also "firm up" an outline by selecting it and stacking copies. Sub-pixel Gaussian blurring and multiplying the new layers may help.
