Photoshop does it, Paint does it. It is just a filter, on a layer of a resized photo. I don't like to do it because I don't want to tape together 15 pieces of 8 1/2 x 11 paper. When I want to do a portrait quilt, I just take a photo to a copy store that has poster sized paper (those that copy blue prints for architects and home builders.) I ask it to be enlarged and pixilated in black and white. Cost is about $15.00 not $45.00 these online services charge and still give you 8 1/2 x 11 paper.