Enhancement of Colour Reproduction for Capsule Endoscopy Images

During a clinical examination, a capsule endoscope, like the PillCam, allows the entire digestive system of the patient to be photographed. The images can be analysed to detect abnormalities. However, the rendering is of low quality compared to colonoscopy. Distorted colour reproduction of tissues and blood vessels can be one reason for overseeing abnormalities, and improvement of colour reproduction could improve the examination. For this purpose, a colourimetric calibration must be performed in order to deduce the correction to be applied. The ColorChecker is a chart containing a number of standard colour patches sampled over the gamut of perceivable colours, providing ground truth reference. Thus, it is possible to measure the rendering of these colours and then compare and adjust its values. However, the colours that appear inside the gastrointestinal system are a subset of perceivable colours. It also appears like typical PillCam’s are constructed accordingly. As shown in this paper, colour correction based on the ColorChecker becomes saturated. Therefore, we develop a novel colour checker based on colours sampled from colonoscopy images and perform corrections based on that. An evaluation of both inter- and intra-camera variation indicates that the same calibration method should perform quite well for all PillCam Colon2 capsules. A subjective evaluation of colour corrected videos was performed by two experienced gastroenterologist, indicating that the proposed method obtains a more faithful colour reconstruction.