A low bandwidth, still image transmission system

Abstract

The Civil Air Patrol (CAP) performs aerial reconnaissance of roadways and bridges. To enhance the analysis of aerial observations, CAP has proposed broadcasting amateur television from aircraft cockpits to ground receiving stations, However, because of the large bandwidth required for video transmission and the low transmitter power available the range of video transmission is very limited. As an alternative to amateur television transmission, the paper develops a software based, continuous-tone, still image transmission system. A digitized color image at television resolution contains nearly one million bytes. Digital imaging is, therefore, not often implemented due to high storage or transmission costs. However, by employing a high quality image compression technique, images may be compressed from 1/10 to greater than 1/50 their uncompressed size without visibly affecting image quality. These compressed images can then be transmitted over a low bandwidth channel in a reasonable time. The major issues in developing the prototype system were the image compression and data transmission techniques. The selected image compression technique is based on the JPEG Still Image Data Compression Standard, known officially as ISO DIS 10918-1 or CCITT Recommendation T.81. The system's data link will use high speed (9600 bits per second) packet radio (CCITT X25). This system shows the JPEG image compression method is suitable for transmitting high quality compressed images over a low bandwidth channel in a reasonable time. Additional data compression is achieved through the use of V.42 bis data compression.