摘要
光子统计噪声是X射线显微成像中影响图像质量的主要因素之一,它对图像质量的影响一般用信噪比来描述.研究表明,X射线显微图像的信噪比随着入射光子数的增加而增加;但由于X射线会对样品带来损伤,所以实验中要求尽量减少入射的X光光子数.但是传统的基于经验数据的罗斯判据并不能给出客观的答案,特别对经过图像减影处理的带噪图像,罗斯判据并不适用.这里提出"区分概率"的概念对罗斯判据进行分析和改进,有助于找出所需最小入射光子数.将区分概率运用到图像减影法中进行模拟,求出此图像处理方法下所需最小入射光子数.最后得出区分概率在0.4时是图像中物体与背景部分得以区分的一个较合理阈值的结论.
Stochastic photon noise is one of the most important factors which influence the quality of X-ray microscope images. The influence of the noise is described by the signal-to-noise ratio （SNR）. Generally, increasing the number of photons yields better SNR, but inevitably with the side effect of a higher dose for the specimens. To find a good balance, one has to find a way to minimize the photon number while keeping an acceptable SNR, but conventional empirical Rose criterion is of little help, especially when applied to processed noised images. Here a concept of ＂probability-to-distinguish＂ was provided as an improvement on the Rose criterion. It can be used to find out the threshold of the photon number. The new method was applied to analyze noised images in image subtraction and compute the minimum photon number required. The conclusion is that objects can be distinguished from their background when the probability-to- distinguish is set at above 0. 4.
关键词
图像衬度
信噪比
罗斯判据
区分概率
图像减影
image contrast
signal-to-noise ratio
Rose criterion
probability-to-distinguish
image subtraction
