  This paper proposes an advanced method for contrast enhancement of capsule
endoscopic images, with the main objective to obtain sufficient information
about the vessels and structures in more distant (or darker) parts of capsule
endoscopic images. The proposed method (PM) combines two algorithms for the
enhancement of darker and brighter areas of capsule endoscopic images,
respectively. The half-unit weighted bilinear algorithm (HWB) proposed in our
previous work is used to enhance darker areas according to the darker map
content of its HSV's component V. Enhancement of brighter areas is achieved
thanks to the novel thresholded weighted-bilinear algorithm (TWB) developed to
avoid overexposure and enlargement of specular highlight spots while preserving
the hue, in such areas. The TWB performs enhancement operations following a
gradual increment of the brightness of the brighter map content of its HSV's
component V. In other words, the TWB decreases its averaged-weights as the
intensity content of the component V increases. Extensive experimental
demonstrations were conducted, and based on evaluation of the reference and PM
enhanced images, a gastroenterologist ({\O}H) concluded that the PM enhanced
images were the best ones based on the information about the vessels, contrast
in the images, and the view or visibility of the structures in more distant
parts of the capsule endoscopy images.
