电影胶片由于长期存放和多次播放，产生了灰尘、污垢、霉斑、图像抖动、划痕、闪烁、噪声、变色、模糊等问题，其中由灰尘、污垢等引起的斑块是出现最频繁的损伤之一。为了快速有效地对这些斑块进行检测，提出了一种检测电影胶片斑块损伤的技术，该技术首先用改进的SROD算法对受损帧的斑块进行初步检测，然后通过两次EM估计算法对检测结果进行后处理来消除噪声的影响，同时确定斑块位置及其边缘信息。实验结果显示，该技术不仅可以有效地检测斑块，而且算法简单快速。

Digital film archives are often damaged by aging and multiple playing, such as dust spots, dirt, blotches, film unsteadiness, line scratches, flicker, noises, color variations and blurs, witch may cause some artifacts on the films. This paper introduces a method for blotch detection. The initial detection is gained by using an improved SROD algorithm. And then postprocessing module is achieved through two EM steps, thus eliminating the effect of noise and determining blotch. Experimental results show that the blotch detection method proposed in this paper is effective and can be easily implemented.