The primary aim of the color constancy algorithm is to estimate illuminant chromaticity. There are various statistical-based, learning-based and combinational-based color constancy algorithms already exist. However, the statistical-based algorithms can only perform well on images that satisfy certain assumptions, learning-based methods are complex methods that require proper preprocessing and training data, and combinational-based methods depend on either pre-determined or dynamically varying weights, which are difficult to determine and prone to error. Therefore, this paper presents a new optimization based illuminant estimation method which is free from complex preprocessing and can estimate the illuminant under different environmental conditions. A strong color cast always has an odd standard deviation value in one of the RGB channels. Based on this observation, a cost function called the degree of illuminant tinge(DIT) is proposed to determine the quality of illuminant color-calibrated images. This DIT is formulated in such a way that the image scene under standard illuminant (d65) has lower DIT value compared to the same scene under different illuminant. Here, a swarm intelligence based particle swarm optimizer(PSO) is used to find the optimum illuminant of the given image that minimizes the degree of illuminant tinge. The proposed method is evaluated using real-world datasets and the experimental results validate the effectiveness of the proposed method.
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Ⅰ. IntroductionIn the real world, the perceived color of an object relies on the surface reflectance and light source color that illuminate the scene. However, the human eye can perceive an object color to be same, even when there is a change in the illuminant color. This ability of the human visual system to discount the influence of illuminant color is referred to as color constancy. In a computational approach, an implied assumption is that the influence of light source colorJournal of The Institute of Electronics and Information Engineers Vol.53, NO.6, June 2016 is static throughout a scene. Therefore, the scene illuminant is estimated first and the scene colors are then corrected using a chromatic adaptation model.The main objective of a color constancy algorithm is to estimate the scene illuminant. However, illuminant estimation is very difficult process and various approximations have been made on physical world scenes to cope up with that. State-of-the-art color constancy approaches can be categorized into three groups: 1) statistical-based methods, 2) learningbased methods, and 3) combinational-based methods [1~2] . The first type of algorithm is based on low level statistics or a physics based reflection model, the second type algorithm makes use of information extracted from the training phase to estimate the light source color, and the third type is formulated by combining statistical-based algorithms or choosing a superlative algorithm for a given image.The Max-RGB or white patch retinex algorithm is a well known statis...