Abstract: A data processing system with a look-up table means for implementing a transfer function with non-uniform resolution comprises a memory to store a plurality of function data; an input to receive external address words for operating on the memory; and an output to provide the function data. The look-up table means comprises a converging means between the input and the memory for mapping specific ones of the external address words onto a specific one of internal address words to access the memory. This greatly reduces memory size. If the transfer function has a symmetry property, a symmetry-handling means further reduces the memory size.

Abstract: A television receiver including a teletext decoder for receiving and displaying teletext pages for signalling that a requested teletext has been changed or not changed with respect to the previous consultation of the relevant page. To this end the receiver forms a checkword upon reception of a teletext page, which checkword is representative of the contents of the page, and compares this with the checkword stored upon previous display of the page.

Abstract: A television receiver includes a teletext decoder which is adapted to check whether a keyword entered by the user occurs in a teletext cycle. The teletext pages with the searched keyword, or their page numbers, are identified and stored for later display or selection. The receiver has arrow keys for selecting the keyword on the display screen so that an alphabetical keyboard is not necessary. The receiver also includes a non-volatile memory in which a personal index of keywords can be programmed.