Observer Performance for a Linear Pattern with Different Frequency Characteristics of Background Random Noise

In the first stage of our investigation, the relationship between the visibility of a low contrast signal on the noisy background and the physical characteristics of digital images has been studied. Although the signal-to-noise ratio (SNR) is widely used as an important index of the image quality, the spatial frequency characteristics of the background random noise also affect significantly on the instantaneous detectability. In particular, the dominance of the higher frequency components on the random noise pattern improves the detectability for the linear signal pattern on noisy images such as X-ray fluorography. In the second stage, an image processing technique that enhances the dominancy of the high frequency components of the background noise without increasing the noise power was proposed and tested by the computer simulation. This technique appears to be quite effective to improve the detectability for noisy images such a digital fluorography on the medical interventional radiology.