A trellis decoding system for use in processing a High Definition Television signal. An optimum ultraviolet dose determining tool, for ultraviolet radiotherapy, is used to determine an optimum ultraviolet dose in advance. The symbolic error covariance propagation model relates input parameters to one another pairwise and in closed form. All electrical, controlling and monitoring functions are incorporated into the two units as shipped requiring only hook-up when the two units are installed at the operational site. The intermediate film layer passes the internal light from the emissive type display panel to the reflective type display panel, and also blocks the external light that passes through the reflective type display panel and is reflected at the emissive type display panel.