An input picture signal is converted, for each picture element, into a K-bit, first time-serial signal having "ls" corresponding in number to the gradation level of the picture element, and the first time-serial signal are written in a random access memory, sequentially updating its column addresses...http://www.google.de/patents/US4368491?utm_source=gb-gplus-sharePatent US4368491 - Driving equipment for multi-gradation level reproduction
