Hue preserving colour image enhancement models in RGB colour space without gamut problem

Abstract

All hue preserving colour image enhancement techniques are associated with the change of colour space, such as RGB to hue saturation intensity (HSI), hue saturation value (HSV), lightness-hue-saturation (LHS), and YUV etc. In these colour spaces intensity or saturation or both have been processed then recombined with unchanged hue component to build a hue preserving method. But all the above techniques are time-consuming for colour space conversion and also introduce gamut problem for which the values of enhanced pixels may not lie within their respective range. In this study, three hue preserving models corresponding to three colour spaces viz. HSI, HSV and YUV, have been proposed by considering only RGB and CMY colour spaces. Any grey level contrast enhancement method can be successfully employed for a colour image through those models. In this paper, a novel variant of Histogram equalisation (HE) has been proposed based on entropy based segmentation to enhance the contrast. The proposed variant called entropy based brightness preserved dynamic histogram equalisation (EBBPDHE) is a modification of brightness preserved dynamic histogram equalisation (BPDHE).