Enhancement of Underwater images using White Balancing and Rayleigh-Stretching

Abstract

Absorption and scattering are the two main issues in underwater image capturing which results in diminished contrast, high level of blurring and faded colours. The present paper proposes a method of enhancing underwater images for better visual quality using auto white balancing followed by gamma correction and Rayleigh stretching in RGB colour model. The proposed method is very effective which does not require any dedicated hardware and depends only on single image. The use of white balancing compensates the non-uniform color cast which is caused by the selective absorption of colors with depth. Histogram stretching of red colour channel is done with a minimum limit of 5% and histogram stretching of blue channel is done with a maximum limit of 95%. Histogram of green channel is stretched in both the directions. To compensate the effect of under and over enhancement from the image, histograms of the stretched colour channels are mapped to trail a Rayleigh distribution. Thorough analysis has been carried out to verify the proposed method. Contrast and image details are effectively enhanced by minimizing the bluish-green effect and reducing less as well as more enhanced areas from resultant image.