Hybrid display system

A cathode ray tube (801 provides a raster scan symbol display superimposed on a stroke vector display, with selected regions of the stroke vector display preferentially masked in response to priority instructions. Stroke vector priority data is loaded into a full-field bit-mapped memory (30) by a raster symbol generator (60) and used to provide a stroke vector masking signal in synchronism with the picture elements of the raster scan. The system provides efficient generation of dynamic stroke priority areas by utilising the repetitive nature of the raster scan to load the stroke priority full-field bit-mapped memory without requiring corresponding processor intervention.