Open a new image in rgb mode. Double click on the background to turn it into an editable layer.

Create a new layer and set blending mode to "Screen." Fill the new layer with white. Click on the eye to hide the new layer.

On your original layer, use the selection tool of your choice: lasso, the marquee or elliptical tools or the single column or row and make your selection. On the options bar, set feather to "6."

Click on the eye on the new layer and fill the layer with black; your original image will now appear. From the options bar: Filter > Pixelate > Crystalize x2.