Zimmerman J B, Cousins S B, Hartzell K M, Frisse M E, Kahn M G
Electronic Radiology Laboratories, Mallinckrodt Institute of Radiology, Washington University, St Louis, MO.
J Digit Imaging. 1989 May;2(2):82-91. doi: 10.1007/BF03168024.
Adaptive histogram equalization (AHE) is a method for adaptive contrast enhancement of digital images. It is an automatic, reproducible method for the simultaneous viewing of contrast within a digital image with a large dynamic range. Recent experiments have shown that in specific cases, there is no significant difference in the ability of AHE and linear intensity windowing to display gray-scale contrast. More recently, a variant of AHE which limits the allowed contrast enhancement of the image has been proposed. This contrast-limited adaptive histogram equalization (CLAHE) produces images in which the noise content of an image is not excessively enhanced, but in which sufficient contrast is provided for the visualization of structures within the image. Images processed with CLAHE have a more natural appearance and facilitate the comparison of different areas of an image. However, the reduced contrast enhancement of CLAHE may hinder the ability of an observer to detect the presence of some significant gray-scale contrast. In this report, a psychophysical observer experiment was performed to determine if there is a significant difference in the ability of AHE and CLAHE to depict gray-scale contrast. Observers were presented with computed tomography (CT) images of the chest processed with AHE and CLAHE. Subtle artificial lesions were introduced into some images. The observers were asked to rate their confidence regarding the presence of the lesions; this rating-scale data was analyzed using receiver operating characteristic (ROC) curve techniques. These ROC curves were compared for significant differences in the observers' performances. In this report, no difference was found in the abilities of AHE and CLAHE to depict contrast information.
自适应直方图均衡化（AHE）是一种用于数字图像自适应对比度增强的方法。它是一种自动、可重复的方法，用于同时查看具有大动态范围的数字图像中的对比度。最近的实验表明，在特定情况下，AHE和线性强度窗在显示灰度对比度的能力上没有显著差异。最近，有人提出了AHE的一种变体，它限制了图像允许的对比度增强。这种对比度受限的自适应直方图均衡化（CLAHE）产生的图像中，图像的噪声含量不会过度增强，但能提供足够的对比度以可视化图像中的结构。用CLAHE处理的图像外观更自然，便于比较图像的不同区域。然而，CLAHE对比度增强的降低可能会妨碍观察者检测到某些显著灰度对比度的能力。在本报告中，进行了一项心理物理学观察者实验，以确定AHE和CLAHE在描绘灰度对比度的能力上是否存在显著差异。向观察者展示用AHE和CLAHE处理的胸部计算机断层扫描（CT）图像。在一些图像中引入了细微的人工病变。要求观察者对病变的存在给出他们的置信度评分；使用接收器操作特征（ROC）曲线技术分析该评分量表数据。比较这些ROC曲线以确定观察者表现的显著差异。在本报告中，未发现AHE和CLAHE在描绘对比度信息的能力上存在差异。
