Detection of Scale Intervals in Digital Images

If an image includes a ruler and some objects, we can estimate the size of the objects manually. In order to achieve a more accurate result, we developed a method for detecting scale intervals on the ruler. In our method, we transfer the digital image into a frequency domain by using Discrete Fourier Transform (DFT) so that a specific frequency appears. This requires that the image has a cyclic pattern such as the scale on a ruler. We can subsequently calculate the scale interval from the detected frequency.