Motion-adaptive standards conversion for broadcast applications

The problem with conventional motion detectors is that the switching from one mode to another is quite noticeable and manifests itself as a variation in vertical detail depending on whether or not an object is moving. A method is described which minimises these switching artefacts whilst maintaining a maximum of vertical resolution in static and moving picture areas. This method is equally applicable to down-conversion and up-conversion processes. Several examples of standards conversion are then considered by extending the concept of a straightforward 2:1 conversion, such as up-conversion to progressive scanning, to the more general case of integer-ratio conversion factors. For example, the conversion from 1152 active lines in the 1250/50/2:1 HDTV standard to 432 active lines in conventional PAL (16:9 letterbox) requires a conversion ratio of 8:3. The design of such conversion filters, which is more critical than that for simple ratios, is also discussed