Lossy compression may lead to the loss of medically relevant information. However, there are no encoding guidelines available for endoscopic videos that specify how to efficiently encode such videos so that the visual quality is appropriate. Hence, most users use inefficient default configurations. Even worse, most commercially available video documentation systems use the legacy MPEG-2 video format, although it is not designed to handle HD content and requires high bitrates. In order to improve storage efficiency, we identified appropriate encoding configurations and studied their impact on the perceptual quality of laparoscopic videos .
In order to investigate how video compression with the H.264/AVC state of the art encoding format and reduced bitrate and resolution settings affects the perceived quality, we performed a subjective study including 37 surgeons and surgical residents. In particular, we addressed to what extend laparoscopic videos can be compressed without any noticeable quality loss. Additionally, we wanted to find out whether it is feasible to reach a significantly higher compression rate without essential loss of “semantic quality”, which refers to the extent to which a video conveys relevant medical information to the observer. The original recordings were encoding using MPEG-2 with a 1080p resolution and a bitrate of 20 Mbit/s. Evaluations results show that using H.264/AVC and a constant rate factor of 26 produces videos with a bitrate of 8 Mbit/s that provide the same visual quality that the original version. Furthermore, we found out that lowering the resolution to 720p, which results in a bitrate of 2,5 Mbit/s, still achieves a good quality. Finally, even a resolution of 640×360 with a bitrate of only 1.4Mbit/s is acceptable. Based on these evaluation results, we propose encoding parameter recommendations for the efficient compression of laparoscopic video archives.