Nighttime Image Enhancement Algorithm Research Based On Histogram Equalization

With the rapid development of computer vision and multimedia technology based on image information,more and more image information is used to address actual application problems,such as production quality inspection,security monitoring,traffic management,film-making and so on.However,due to the conditions such as bad weather,insufficient illumination and over-exposure,the captured nighttime images are often too dark and non-clear to see the details.Therefore,it has been a hot-spot and task how to improve the quality of images effectively and quickly so as to reflect the real situation of the environment well.Enhanced image grayscale distributions using the traditional histogram equalization algorithm often lose details because of not completely uniformity.Moreover,the original grayscale may become equal after processed and easy to produce pseudo-contour defects.Thus,in this paper,an exact histogram equalization algorithm has been proposed to solve these problems.The gray level distribution of the histogram is almost completely uniform,which can better expand the dynamic range.Because the classical histogram equalization algorithm usually causes color distortion,and the exact histogram specification algorithm is difficult to select an appropriate intensity mapping function and it's also affected by the image non-edge pixel.Therefore,a new edge-guided exact histogram specification method for enhancing nighttime images was proposed in this paper.The EGEHS operates in the HSV color space.Firstly,the gradient image is calculated in the V-channel.Secondly,we sets the threshold to find the edge region of the V-channel and apply the resulting intensity mapping function to the whole image.Finally,the significantly enhanced nighttime images are obtained through combing three channels.The experimental results demonstrate that the EGEHS outperforms the other six comparison algorithms in the three objective evaluation indicators.And the enhanced image using the EGEHS is also optimal in the subjective vision.The brightness,contrast and sharpness of the nighttime image are preserved,and the detail information is retained to a greater extent.What's more,the proposed method achieves state-of-the-art for enhancing extremely dark images,which is thebiggest feature of our method.