Balancing of Attenuation Disparity to Restore the Weak Color Channels in Underwater Images

Abstract

The images captured under water are typically deteriorated due to non uniform attenuation of traversing light in underwater medium. The studies on underwater environment mainly depends on the techniques for the enhancement of underwater images. Many state-of-the-arts compensate the losses due to scattering of light in underwater images but still it is a challenging task to compensate the color distortion due to absorption of light. A new approach is introduced in this article for the enhancement of underwater images by balancing the attenuation disparity between the color channels. This approach reduces the color dominancy based on the prior that the non-uniform attenuation of RGB channels of light in water which results in severely absorbed, moderately absorbed and informative color channels. The difference between the maximum pixel intensity level of an image and its color channels is considered as the attenuation disparity of color channels. So, this leads to the statistical classification of underwater images into five major types: haze, bluish, greenish, greenish blue and bluish green images and two special types such as yellowish image and dark image subjectively. The pixel intensity of severely and moderately absorbed color channels are manipulated in accordance with the informative color channel by adding the value of concerned attenuation disparity globally. It increases the pixel intensity level of weak color channels and restores the channel information but does not improve the visual quality. The Gray World (GW) method or color equalization (CE) method is applied to remove the color imbalance and the contrast is improved by saturating the high level and low level pixel intensities. Finally, the conventional multiscale image fusion is employed to improve the image quality. The experimental results show that the proposed method outperforms qualitatively and quantitatively in terms of underwater color image quality evaluation (UCIQE) metrics and underwater image quality measures (UIQM) compared to the existing image enhancement methods.

Keywords

• Attenuation disparity
• attenuation of light
• color equalization
• Gray World assumption
• image enhancement
• underwater image classification