X线照片密度与图像灰度之间的关系

Relationship between the Optical Density of X-Ray Film and Gray Scale of Image

目的 研究X线照片密度与图像灰度之间的关系。方法 采用 2 4阶X线标准密度片作为实验对象 ,首先设置实验参数 ,选择不同的分辨率与γ值 ,把X线标准密度片经数字化仪扫描 ,相同扫描参数进行 5次扫描 ,输入计算机 ,在计算机上测量出X线标准密度片的各阶灰度值 ,取 5次扫描所得灰度值的平均值 ,作为最终各阶灰度值 ;然后 ,分析、比较灰度值与相应各阶密度值之间的关系 ,建立数学模型 ,通过计算均方误差最小 ,求X线照片密度与图像灰度之间的关系式。结果 在分辨率 ppi=40 0、γ =0 .9,密度范围 :0 .166～ 3 .2 0之间时 ,得到X线照片密度与图像灰度之间的关系式 ,其标准估计误差是 :0 .0 411。结论 应用本研究所得关系式 ,实现了X线照片密度与图像灰度之间的转换。本研究为X线照片密度测量及数字化像质评价提供了一种科学、有效的方法。

Objective To study the relationship between the optical density of X ray film and the gray scale of image. Methods The X ray standard density film was used as the experiment subject in this paper. The images of the X ray standard density film were acquired with the different value of γ and resolution with a digitizer (AGFA DUSCAN T2000XL) and five images were obtained with the same scanning parameter, then the gray level of the image measured on the computer was the average of gray level of the five images. The maths model based on the relationship between the value of the density and the gray level was established and resolved by using the minimum mean square error fitting. Results The formula on the relationship between the optical density of X ray film and the gray scale of image was established when the value of γ and resolution were 0.9 and 400 respectively, and the range of the optical density of X ray film was from 0.166 to 3.20. The standard error of the estimation was 0.0411 . Conclusion The optical density value of X ray film can be obtained from the gray level of the image by using the formula. A scientific and efficient method for the measurement of X ray film density and the quality evaluation of X ray film is provided in this paper.