Maintaining the mean luminance of decoded HD-MAC signals

The disparity between the luminance of areas of the picture processed through different branches of HD-MAC BRE bandwidth reduction encoder, caused by applying spatial filters to gamma-corrected signals, has been minimised by adjusting the mean level of the signal. This does not require linearised signals to be used throughout the studio, which need wider data paths, nor does it introduce new high frequencies by linearising signals within the BRE. Three techniques have been described to correct the additional losses incurred in motion-compensated temporal interpolation with imprecise motion vectors. These techniques give different trade-offs between decoder complexity, flexibility for changes in receiver design in the future and compatible picture quality. The choice of the best compromise is currently under consideration