Skew Rectification for Yarn-dyed Fabric via FFT in HSL Color Space

The texture of yarn-dyed fabric image has been analyzed in HSL color space. With Fourier transform, periods of the pixels in a line are obtained. By comparing the periods in different lines, a conclusion that if the line is parallel to the yarns, sum of periods for the three components (H,S,L) comes to minimum, is proposed in this paper. By this conclusion, the center of fabric image is chosen as skew rectification point. All the lines within plusmn 20 degree are traversed with a step 0.2 degree, and the periods of H,S and L for the pixels in these lines are all calculated with FFT. By sum the three periods of each line, 101 sum values are obtained. Then the position of yarns can be located by finding the line with minimum period. This method is proved efficiency by the experiment, with a precision of 0.2 degree.