I have had difficulty finding "preferences", there is "options", but didn't seem to be what you were referring to. I did find a filter option under Image Attributes on the bar on the right, for making your image "drawn", "pastel", "painted", b/w", etc. Mine was switched to "none". Is this the filter option you were referring to? I don't think this option really controls pixilation. Must be somewhere else. I'll keep looking. :-)