Cut off frequency for a 2D image filter

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Kyle
Kyle 2016-12-16
I'm reading a paper to study 2D image filter. The paper smoothed an image by a first order Butterworth low-pass filter with a cutoff frequency of 0.05 cycles per millimeter.
I'm trying to implement this method but I have a bit difficulties to understand the cut-off frequency. I have an image with the size 600 x 500, and the pixel size is 0.5 millimeter per pixel. So the image has the width 250 mm and the height 300 mm.
After doing fft2(), I converted the image to frequency domain. I understand that the x axis takes the unit cycles per 250 mm, and the y axis takes the unit cycles per 300 mm.
For example, a 'pixel' (10, 10) in the frequency domain image should read 10 cycles per 250 mm at x direction and 10 cycles per 300 mm at y direction.
Going back to the mentioned cut-off frequency of 0.05 cycles per mm, should I look at an x limit at (250 * 0.05), and y limit at (300 * 0.05) at the x and y axis of the frequency domain image?

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