A singular-value-decomposition analysis of the imaging kernel for three-dimensional fluorescent laser scanning microscopy at a high numerical aperture (NA) is presented. The design and superresolving performance of image-plane binary optical masks are then derived, and new computational techniques for calculating these masks are given. Initial experimental results with a microscope equipped with such a mask at NA = 1.3 are presented. The improvement in both contrast and resolution over the confocal and type 1 instruments is demonstrated. (C) 1998 Optical Society of America.