A video system for transmitting hidden pictures based on CCITT T.4 2-D compression

The use of vertical blanking intervals in a PAL video signal for transmitting an animation of 112/spl times/128 dots of black and white picture is proposed. Data compression based on CCITT T.4 2-D standard and low data rate of 500 kbit/sec are chosen to make the hardware design of an inserter and decoder economically feasible to using an 8-bit microcontroller. The inserter is designed to hide 48 bytes of compressed data, generated by a personal computer, within lines 7 to 22 of a PAL video signal. The decoder can extract these data, decompress and display the hidden picture on the lower right position of a normal TV screen. The basic building blocks of these two devices will be described. This system can be used to provide a Sign Language Closed Caption service.