Colour Contrast Enhancement Method by Scaling the DC Coefficients in CIE-LAB Colour Space

Abstract

Colour and brightness of the captured images from low cost digital cameras are usually different from the colour and brightness of the original scene. Many factors are responsible for the low contrast images such as non uniform illumination, large or small exposure of some specific regions, and the unwanted movements of camera users. Due to these reasons the captured image to looks annoying to human visual system. Thus, contrast enhancement methods are required for improving the visual appearance of the colour images. In this paper the performance of contrast limited adaptive histogram equalization (CLAHE) method is compared with method of DC coefficient scaling in the compressed DCT domain for enhancing the contrast of colour images. In addition, as a modification DC coefficient scaling is also implemented in the CIE-Lab colour space. The contrast is only enhanced in L component and keeping the colour information preserved. This improves the entropy of standard method. For comparing the performance along with SNR and entropy the absolute standard deviation difference is also used as parameters. The methods are tested on various true colour images from different environment. General Terms Image processing, Image enhancement, Colour spaces