The Study Of Auto-exposure And Auto-gain On CCD Imaging Electronics System

This topic comes from an actual development project of high-resolution CCD imaging electronics system, and I am responsible for the study of auto-exposure and auto-gain of the system based on FPGA.Currently, the resolution of camera system is not high. In the specific application environment of needing to analyse some details of the scene, the popular camera system in the market can not meet the requirements. Therefore, high-resolution camera system has great practical needs. And the auto-exposure and auto-gain are essential components of functions of camera system.For an imaging system, the light intensity of the scene, aperture size, exposure time and signal gain determine the brightness of the image. In nature, the natural light intensity determines the light intensity of the scene; one can not easily control it. Therefore, in order to automatically obtain moderate-brightness images, it is only needed that the aperture size, exposure time and signal gain are effectively controlled. In this system, the aperture size is manually controlled, and exposure time and signal gain are automatically controlled.The purpose of auto-exposure is to obtain moderate-brightness images by imaging system automatically exposing to the objectives. Generally it includes three steps:light intensity measurement, scenario analysis and exposure compensation. And auto-exposure has optics-implemented way and electronic-implemented way. The purpose of auto-gain is to adjust the image brightness by automatically adjusting the gain of amplifiers based on the image brightness.To obtain moderate-brightness images, our group propose auto-exposure and auto-gain algorithm based on the gray-average and the dynamic-range of histogram, taking the exposure time as a prerequisite, adopting electronic-implemented way, and determining the light environment by analyzing the distribution of the histogram. Algorithm based on function is divided into Dynamic-distribution Adjustment Module, Gray Statistics Module, Gain and Exposure-time Conversion Module, Gain-code Lookup Module, Shutter Control Module, etc. And algorithm is programmed using the Verilog language, and implemented on FPGA hardware platform. Currently, the software and hardware of the system have been completed; also the debugging of the whole system has been completed. The performance of auto-exposure and auto-gain algorithm is also verified by experiment. At present, the system is stable, images are clear.