2. Endoscopic image pre-processing

2.1 Barrel distortion

Endoscopists generally observe the tissue surface very closely, to benefit from very good image resolution. The distal tip of endoscopes is located at a distance ranging from one to several centimetres from the tissue under observation. This distance of observation requires wide-angle (wide-field) optics to ensure a minimum field of view of the order of a few square centimetres. Wide-field optics require short focal lengths, leading to "barrel" distortions.