针对机器视觉中存在的离焦现象，采用理论与实验相结合的方法分析了离焦成像对面积测量的影响.实验表明,当离焦量（物面偏离对准平面的距离）为10 mm时，面积相对误差达31.3%.根据图像最大梯度值与离焦量之间的关系提出了一种误差修正的方法.首先标定图像最大梯度值与离焦量之间的关系，然后求待测图像的最大梯度值，由最大梯度值求出离焦量，最后根据离焦量对图像面积进行修正.结果表明,当离焦量小于10 mm时，经修正后图像面积相对误差小于3.8%.

Phenomenon of defocus in machine vision, the effect of defocused image on aTo therea measurement was analyzed by the method of theory and experiment.The results of experiment show that the relative error is 31.3% when the object plane deviates 10 mm from conjugate plane.A method of amendment error was developed according to the relation between maximal image gradient and defocusing amount.The relation between maximal image gradient and defocusing amount was calibrated.The maximal gradient of image was calculated.The defocusing amount was deduced.And,the area of defocused image was amended according to the defocusing amount.After amendment,the relative error of image area is less than 3.8%,when the defocusing amount is within 10 mm.