Original
Downsampled preview
Limits the pattern to this many DMC threads. Pixels are snapped to the nearest of these once the limit is applied.
Direct match snaps each region to one flat colour. Atkinson spreads a small part of each colour choice's error to neighbouring stitches, the way traditional image dithering works.
Pattern preview
Only merges a stitch if this much of the area around it already shares one colour, so real detail (like facial features) is left alone.