Abstract: To solve the problems of the ringing, blocking artifacts and the excessive noise amplification in local image enhancement, an object-based multilevel contrast stretching method was proposed. First, segment the image into its constitent objects by using morphological watersheds and regional merging; then, separately stretch the image contrast at inter-object level and intra-object level in different ways. At inter-object level, an approach of stretching between adjacent extrema was adopted to adequately enlarge the local dynamic range of gray levels between objects; at intra-object level, the linear stretching approach was adopted to enhance the textural feature of the object and keep its appearance. Experimental results show, besides enhancing the image structure, the proposed method can effectively avoid ringing, blocking artifacts, restrict excessive noise amplification in smooth areas and preserve the overall brightness of the image, thus can provide the enhanced image with natural appearance.

Key words: image enhancement, image segmentation, morphological watershed, region merging, contrast stretching

摘要： 针对图像局域增强时出现的噪声过增强和环块状伪轮廓问题，提出了基于对象的多级对比度拉伸图像增强法。首先采用形态学分水岭及区域合并法对图像进行分割，得到图像的构成对象；然后在对象之间采用相邻极点间拉伸法增大对象间灰度动态范围，在对象内部采用线形拉伸法增强对象纹理并保持对象形态。实验结果表明，该方法在增强图像结构的同时，能够有效避免环块状伪轮廓,抑制平滑区域噪声过增强,保持图像原始整体亮度，使增强后的图像具有自然的外观。

关键词: 图像增强, 图像分割, 形态学分水岭, 区域合并, 对比度拉伸