CLAHE和细节放大相结合的档案图像增强方法

图像增强可提高扫描档案图像的质量，关系到档案图像信息系统的生命。运用CLAHE可以进行全局对比度拉伸，运用Lee滤波器可进行局部细节放大，将两者结合可形成放大细节的CLAHE方法。对结合的方法从两方面进行改进，一是引入噪声抑制措施，使得Lee滤波器只放大图像细节而不放大噪声；二是制定柔性细节放大机制，使得细节放大更加符合人类视觉习惯。改进后的方法既能提高全局对比度，又能有效放大局部细节。实验表明，提出的方法对包含文本、图形和图像的扫描档案具有较好的增强效果，且能够满足国家行业规范要求和实际应用需要。

A method of document image enhancement based on the combination of CLAHE and detail amplifying

The document image incorporating with image enhancement method can achieve a good perceptual quality, which is necessary for the document image information system. Contrast-limited Adaptive Histogram Equalization (CLAHE) is widely utilized to expand the global dynamic contrast range, and Lee filter is usually used to amplify the local details. A detail-amplifying CLAHE (DAHE) method is proposed by combining the above two methods. Firstly, a noise-resist policy is employed to differentiate the detail and the noise. Secondly, a flexibility amplifying mechanism is proposed to make the amplified image suitable for the human vision system. The proposed method can not only balance the global gray-level dynamic range, but also enhance the local details. The experimental results demonstrate that the proposed method can both enhance the document image, which is suitable for the document image information system, and satisfy the requirements of the national industry standard.