Research On Real-Time Distortion Correction And Automatic Brightness Control Hardware System For Medical Electronic Endoscope

Medical Electronic Endoscope (MEE) is a widely used medical instrument to cure various diseases. Because wide-field lens are adopted in MEE, output images have serious distortion. Software, limited by computer's calculating speed, can only correct the distortion of static images but not the distortion of dynamic images. So we use the high speed character of very large scale integration (VLSI) to reach real-time need. Otherwise, due to the complexity of the inside illumination of the patient's body, the result depends on the ability of brightness control. A high-performance and complete-function brightness control system is designed. Image distortion correction includes spatial correction and gray-level correction. This paper is based on the dot-array plate correction method. Standard dot-array plate is placed in front of MEE, after whose optical system the distorted dot-array plate image is received. In comparison the standard dot-array plate image with the distorted one, the distortion function can be found to implement spatial correction. The correction datas form the loop-up table and are stored into the flash EPROM. The accuracy of hardware correction is decided by the accuracy of software correction. The hardware bilinear interpolation has good accuracy and can correct general images. The bilinear interpolation module is designed using the language of Verilog HDL and simulated using the software of Quartus II. FPGA is used as the core of the whole system. The I2C communication of video decoder and encoder is completed. FPGA can read or write the SRAM and flash EPROM. The design of every circuit module is detailly explained. The hardware bilinear interpolation is introduced in the fourth chapter as an emphasis. The automatic brightness control system is another design. The design includes the average and peak area exposure measurement using FPGA. By using two modes in turn, the brightness control system is realized. At the end of this paper, we analyze the error source of distortion correction hardware system, compare the effect of distortion correction, summarize the characters of system and put forward the improvement way. This hardware system works in NTSC; field frequency is 60Hz; size of correcting image is 640x480 pixels; input and output are both standard video signals so that corrected images can be displayed on monitor directly. In distortion correction aspect, the distorted image's relative distortion is –20.86% and the corrected image's relative distortion is -1.60%, so we can conclude that the hardware system effectively reduce the distortion of optical system. In real-time aspect, delay time between distorted images' input and corrected images' output is 40ms.so the hardware system reaches the demand of real-time character.