Underwater Image Enhancement Using Integrated Contrast Correction And White Balance Methods

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Date
2009-03
Authors
Kashif Iqbal
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Abstract
The clarity of underwater images is degraded by light absorption, scattering of light and turbidity of water. Due to this, underwater images are affected by bluish colour cast, low contrast and reduced illumination. This thesis proposes two approaches "Integrated Colour Model" (ICM) and "White Balance Adaptive Approach" (WBA) to address factors affecting image clarity. The ICM is based on colour balancing, contrast correction of RGB colour model and contrast correction of HSI colour model. Firstly, the colour cast is reduced by equalizing the colour values. Secondly, an enhancement to a contrast correction method is applied to increase the Red colour by stretching red histogram towards the maximum (i.e., right side), similarly the Blue colour is reduced by stretching the blue histogram towards the minimum (i.e., left side). Thirdly, the Saturation and Intensity components of the HSI colour model has been applied for contrast correction to increase the true colour using Saturation and to address the illumination problem through Intensity. The WBA approach is based on contrast correction and white balance algorithms. A new efficient process for colour cast adjustment is introduced which relies on statistical calculations. This is performed by determining the colour cast, calculating the intensity ratio between RGB components and correcting the affected image by applying two gain factors (i.e., Red and Green). Both the ICM and WBA models have been evaluated using the three wellknown methods: Human Perception, Edge Detection and Histogram. The use of three different methods ensures that the proposed models are comprehensively evaluated. The proposed approaches: ICM and WBA are compared with the established methods (i.e., Gray World, Histogram Equalisation and White Patch) and the latest research methods. The results show that both the ICM and WBA have outperformed against the established methods in terms of colour enhancement, contrast and illumination. The latest research methods: (i) use artificial illumination to capture clear reference image; (ii) use predefine threshold values; (iii) involve computationally intensive local and global enhancement process and; (iv) regenerate the absorbed wavelength of light using known depth of the scene. In some cases, the latest research methods have achieved better results due to the fact that they have used additional information (i.e., artificial illumination, predefined threshold values and reference image) but the use of such information can reduce the adaptability of the methods. Additionally WBA shows significant results when applied to underwater videos and land images.
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The clarity of underwater images , is degraded by light absorption
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