The detection of blotches in old movies

Blotch detection is one of the most important steps in the old movies restoration. The existing blotch detection algorithms get higher correct detection rates by reducing the threshold value. However, the corresponding higher false alarms affect the following correction results directly. To maximize the ratio between correct detections and false alarms, an improved blotch detection algorithm based on simplified rank-ordered difference is proposed in this paper. The improved algorithm can achieve the most appropriate threshold for the different blotches in one frame by introducing dual-step adaptive multi-threshold; meanwhile the employment of texture matching avoids the possible deviation caused by motion vector estimation in the regions with blotches. Performance evaluation is taken to the image sequences with both real blotches and artificially corrupted ones separately. The experimental results indicate that our algorithm can achieve higher correct detection rates and lower false alarms.