直方图匹配与直方图均衡化对比度校正方法：比较

Histogram-matching and histogram-flattening contrast correction methods: a comparison.

作者信息

Hildebolt C F, Walkup R K, Conover G L, Yokoyama-Crothers N, Bartlett T Q, Vannier M W, Shrout M K, Camp J J

机构信息

Washington University, St. Louis, Missouri, USA.

出版信息

Dentomaxillofac Radiol. 1996 Jan;25(1):42-7. doi: 10.1259/dmfr.25.1.9084285.

DOI:10.1259/dmfr.25.1.9084285

PMID:9084285

Abstract

OBJECTIVES

To compare the results or two methods of histogram matching and two methods of histogram flattening for their ability to correct for contrast variations in digital dental images.

METHODS

A custom-built, aluminium stepwedge with 0.1, 0.5 and 1.0 mm steps was placed over Ektaspeed films and exposed for 0.06, 0.12 and 0.25 s, respectively. Radiographs were digitized at 50 microns spatial resolution and 12-bit contrast resolution. Contrast corrections were performed using Rüttimann et al.'s algorithm (1986) for one method of matching (RM) and flattening (RF) and Castleman's algorithm (1979) for the other method of matching (CM) and flattening (CF). Mean pixel grey-scale values were determined for each step. The 0.12 s exposure was considered to be the target image exposure. Absolute differences in pixel grey-scale values between the target images and the modified images were determined.

RESULTS

The median values of the absolute differences in pixel grey-scale values between the target images and the contrast corrected images were: CM = 4.3; RM = 4.1; CF = 70.2 and RF = 70.2.

CONCLUSION

Castleman's and Rüttimann's matching algorithms perform equally well in correcting digital image contrast. Histogram flattening was less effective.

摘要

目的

比较两种直方图匹配方法和两种直方图均衡方法对数字牙科图像对比度变化的校正能力。

方法

将一个定制的、具有0.1、0.5和1.0毫米阶梯的铝制阶梯楔形物放置在爱克发速成像胶片上，并分别曝光0.06、0.12和0.25秒。以50微米的空间分辨率和12位的对比度分辨率对X光片进行数字化处理。使用鲁蒂曼等人（1986年）的算法对一种匹配（RM）和均衡（RF）方法进行对比度校正，使用卡斯尔曼（1979年）的算法对另一种匹配（CM）和均衡（CF）方法进行对比度校正。确定每个阶梯的平均像素灰度值。将0.12秒的曝光视为目标图像曝光。确定目标图像与修改后图像之间像素灰度值的绝对差值。