This document discusses and defines three types of filters in Photoshop: blur filters, sharpen filters, and noise filters. Blur filters are useful for adding depth of field or covering flaws, and can create realistic lens blur or speed effects. Sharpen filters help correct imperfections and emphasize elements by increasing contrast between pixels. Noise filters allow adding or reducing noise and grain in photographs, with the reduce noise filter being useful for repairing old or damaged photos and the add noise filter having creative uses.