Film restoration using image processing has been an active research field during the last years. However, the restoration of the soundtrack has been mainly performed in the sound domain, using signal processing methods, in spite of the fact that it is recorded as a continuous image between the images of the film and the perforations. Digital restoration of optical soundtracks at the image level is an application field which has not been investigated, though it is scientifically rich. It consists in removing dust particles, concealing large corrupted areas or restoring underexposure or overexposure defects of the soundtrack. Finally, it makes it possible to mix image processing and signal processing approaches.After introducing the principles of optical soundtrack recording and playback, this contribution focuses on experimental approaches to detect and cancel the effects of under and overexposure. The approach is validated on both simulated alterations and real data digitized using the specific optical soundtrack scanner we have set up for the RESONANCES project.