Abstract
Defogging algorithms based on dark channel prior have color shift in light color areas because of inaccurate estimation of transmittance. To resolve this problem, a novel improved image clearness method is proposed. Based on the dark channel prior, the essential causes of color shift are analyzed, with two important factors summarized. Then, transmission map is calculated by using 3⁎3 fixed region, and the restoration module based on self-adaptive threshold mechanism for transmission map is provided. Some experiments are carried out to determine parameters in restoration module to correct the transmission map. According to the corrected transmission map, a transmission restoration algorithm is constructed based on the self-adaptive threshold mechanism to improve the performance of the fog-free image. The experiment results show that this method can resolve the color shift in light color areas effectively and guarantee the overall framework of defogging method based on dark color theory unchanged.
Highlights
In fog weather, due to the influence of atmospheric scattering, image taken by outdoor surveillance system would get serious degradation problems in the color and contrast fidelity
The defogging algorithm based on dark channel prior (DCP) is simple and effective; the inaccurate estimates of transmission would lead to distortion of the image, such as halo artifacts and overly enhanced restoration in light color areas, and the optimization algorithm of transmission has high spatial complexity
Based on DCP, this paper proposes an improved algorithm combined with self-adaptive threshold mechanism (STM), which enhances the transmittance in light color area
Summary
Due to the influence of atmospheric scattering, image taken by outdoor surveillance system would get serious degradation problems in the color and contrast fidelity. Zhu et al [18] exploited the characteristics of brightness and saturation of the pixels in hazy image, proposing a new linear model and learning the parameters of the model by using a supervised learning method to estimate the depth information Their experimental results indicated that dehazing effects are good and efficient, but the insufficient estimation of transmission map is still an unsolved problem. The remaining parts of this paper are arranged as follows: in Section 2, atmospheric scattering model will be introduced briefly; in Section 3, the original defogging algorithm based on dark channel prior theory will be described in detail; Section 4 performs a detailed analysis of the color shift problem and construct an improved algorithm combined with self-adaptive threshold mechanism (STM).
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