Abstract:
This dissertation proposes a system that uses the vertical blanking intervals of a PAL video signal for transmitting and receiving a sequence of animation pictures, each of which consists of 112 X 128 dots of either black or white. A data compression technique based on the CCITT T.4 2-D standard is adopted by the system to reduce the amount of transmitting data per picture by an average of 5-10 times with no loss of information. Yet, its decompression algorithm is still simple enough to be implemented at the receiver in real time by a high speed 8 bit microcontroller. Two pieces of hardware, i.e. an inserter and a decoder, are developed to test the proposed system. The inserter is designed to hide 48 bytes of compressed data, generated by a personal computer, in 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. Preliminary analysis has indicated that this system can support an animation rate of 6 hidden picture frames per second. Therefore, it has a good potential for providing a sign language closed captioning service.