US Patent 7518608 Z-depth matting of particles in image rendering

A method of rendering a first image having a plurality of particles. The method comprises: receiving a z-depth image that provides a z-value for each pixel in the first image; generating a single pixel particle of an opaque transparency for each pixel in the z-depth image positioned at the same x-y position as the each pixel in the z-depth image and at a z-position indicated by the z-value; sorting the plurality of particles with a plurality of the generated single pixel particles in the first image based on the z-position; and rendering the sorted plurality of particles and single pixel particles based on the sorted order.