where a is a lower cutoff level and b is a higher cutoff level of a band-pass filter (Fig. 7). Usually, only the high-pass filter is used to calculate the intensity of orientation (b = N).
The influence of the high-pass filtering on orientation intensity can be visualized by the reconstruction of the images using an inverse FFT after the masking of the low-frequency component (Fig. 8).
In the image of the trabecular bone, low-frequency components constitute bulk density of the trabeculae. High-frequency
FIGURE 7 Coordinate transform from Cartesian to polar using a linear interpolation (A). Angular distribution analysis of frequency transform (B). The intensity of orientation at an angle of 6 is calculated as a summation of the power spectrum in a segment in a narrow fan-shaped area (shown as a gray area).
Power spec Dtini
Linear Interpolation
Power spec Dtini
Fine structure such as collagen fiber is more suitable for Fourier analysis.
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