Sentence:  Films corrupted by <WSD>blotches</WSD> are often restored in a two-step approach. The first step detects <WSD>blotches</WSD> and generates binary detection masks that indicate whether each pixel is part of a <WSD>blotch</WSD>. The second step corrects pixels by means of spatio-temporal interpolation. 
Meaning of the word marked with <WSD> tags:  A bright or dark spot on old film caused by dirt and  loss of the gelatin covering the film, due to age and poor film quality.