目的 为了解决纸塑复合袋的缺陷图像筛选效率低、精度差等问题，提出一种基于梯度投影差值的纸塑复合袋表面缺陷图像筛选方法。方法 首先采集纸塑复合袋图像，并利用Sobel算子函数得到其梯度幅值图像，使用水平投影和垂直投影计算公式，计算获取的梯度幅值图像信息，得出图像水平和垂直方向的投影均值，采集缺陷图像中具有丰富梯度信息的特点，分析梯度投影均值的差值，根据图像信息计算出阈值，通过比较投影差值和阈值，完成图像的筛选。结果 针对此次采集的缺陷图像，当投影差值阈值设置在0.014 6~0.018 9内时，可以筛选出表面缺陷的图像。相较于差影法，该方法的筛选正确率提高了约10%，图片筛选时间加快了1.5 s。结论 文中提出的梯度投影差值方法与差影法相比，具有图像筛选正确率高、筛选速度快等优点，满足图像筛选在工业生产上的需求。

The work aims to propose a surface defect image screening method for paper-plastic composite bag based on gradient projection difference, so as to solve the problem of low efficiency and poor accuracy in defect image screening. Firstly, the image of paper-plastic composite bag was acquired and the gradient magnitude image was obtained by Sobel operator function. Then, the information of the acquired gradient magnitude image was calculated by the horizontal projection and vertical projection calculation formula, and the average value of horizontal projection and vertical projection of the image was derived. The difference in average value of gradient projection was analyzed according to the feature of abundant gradient information in the acquired defect image, and the threshold value was calculated according to the image information. The screening of the image was completed by comparing the projection difference and the threshold value. For the acquired defect image, when the threshold value of projection difference was set in the range of 0.014 6 to 0.018 9, the image of surface defect could be screened. Compared with the differential shading method, the screening correct rate of this method was improved by 10% and the image screening time was accelerated by 1.5 s. The gradient projection difference method proposed has the advantages of high correct image screening rate and fast screening speed compared with the differential shading method, which can meet the needs of image screening in industrial production.