Fig. 17From: Acquisition of a single grid-based phase-contrast X-ray image using instantaneous frequency and noise filteringBasic concept of an adaptive Gaussian notch filter: a image, b Fast Fourier transform (FFT) amplitude distribution, c removal of the frequency components of the periodic noise using segmentation and extraction algorithms and FFT amplitude distribution with the frequency components removed, and d final filtered image. fx: x-axis spatial frequency; fy: y-axis spatial frequencyBack to article page