OTSU Guided Adaptive Binarization of CAPTCHA Image using Gamma Correction

CASIA OpenIR > 复杂系统管理与控制国家重点实验室 > 影像分析与机器视觉

	OTSU Guided Adaptive Binarization of CAPTCHA Image using Gamma Correction
	Shi Cunzhao; Wang Yanna; Xiao Baihua; Wang Chunheng
	2016
会议名称	International Conference on Pattern Recognition(ICPR)
会议录名称	ICPR
会议日期	2016.12.4-2016.12.8
会议地点	Mexico
摘要	Gamma correction, a nonlinear operation, has long been used to code and decode luminance or tristimulus values in video or still image systems [1]. In this paper, we make the following observations: for CAPTCHA images which could not be well binarized using the threshold of OTSU, there exists a gamma corrected image which could be well segmented by the OTSU threshold and the value of the best gamma could be revealed by observing the maximal inter-class variance (MICV) values of different images transformed by different values of gamma. Concretely, we convert the R, G, B channels of the original CAPTCHA image with different gamma values and transform the color images to gray-level images. Each gray-level image could be then segmented by the threshold acquired by OTSU. By linking each gamma value with the corresponding maximal inter-class variance value, we could draw a changing curve of variance values versus gamma. The best gamma could be acquired by finding the point whose related MICV starts to change slowly. Moreover, the polarity of the image could also be revealed by the changing trend of the curve. Experimental results on different categories of CAPTCHA images demonstrate the effectiveness of the observations for binarizing the CAPTCHA images and telling the polarity as well.
关键词	Binarization Gamma Correction Captcha Image
文献类型	会议论文
条目标识符	http://ir.ia.ac.cn/handle/173211/12088
专题	复杂系统管理与控制国家重点实验室_影像分析与机器视觉
通讯作者	Shi Cunzhao
推荐引用方式 GB/T 7714	Shi Cunzhao,Wang Yanna,Xiao Baihua,et al. OTSU Guided Adaptive Binarization of CAPTCHA Image using Gamma Correction[C],2016.

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