Colour Separation Overlay and its relation to digital video sampling

Current techniques for color separation overlay (CSO) are briefly described. The influence of CSO techniques on the formulation of standards for digital video sampling parameters is discussed and experiments are described which investigated the effects on CSO pictures of filtering and sampling the foreground picture signals. The conclusions are that a chrominance (UV) bandwidth of at least 3 MHz, (implying a sampling frequency of at least 6 MHz) is needed for satisfactory CSO whereas luminance (Y) sampling frequency need not be constrained by CSO considerations. Hence a YUV sampling frequency standard of 13.5, 6.75, 6.75 MHz appears to be commensurate with good-quality CSO. This investigation into digital video sampling parameters formed part of the evidence on which the 13.5:6.75:6.75 system was chosen for digital video sampling.