High-speed camera with internal real-time image compression

Abstract

High-speed video cameras are powerful tools for investigating, for instance, fluid dynamics or the movements of mechanical parts in manufacturing processes. In the past 5 years the use of CMOS sensors instead of CCDs has facilited the development of high-speed video cameras offering digital outputs, readout flexibility, and lower manufacturing costs. Still the huge data flow provided by the sensor cannot be easily transferred or processed and thus must generally be stored temporarily in fast local RAM. Since this RAM is size limited, the recording time in the camera is only a few seconds long. We tried to develop an alternative solution that would allow continuous recording. We developed a real-time image compression in order to reduce the data flow. We tested three algorithms: run-length encoding, block coding, and compression using wavelets. These compression algorithms have been implemented into a FPGA Virtex II-1000 and allow real-time compression factors between 5 and 10 with a PSNR greater than 35dB. This compression factor allowed us to link a new high-speed CMOS video camera with a PC using a single USB2 connection. The full flow of 500 fps in 1280x1024 format is transferred to the computer in real-time.