An illumination-independent edge detection and fuzzy enhancement algorithm based on wavelet transform for non-uniform weak illumination images

An illumination-independent edge detection and fuzzy enhancement algorithm based on wavelet transform is proposed to extract edges out of the non-uniform weak illumination image. Firstly, to work out the illumination-independent edge detection method based on wavelet transform, the illumination-reflection image formation model and CCD camera imaging formula are introduced. In succession, the pixels’ wavelet module coefficients in the local edge area of the image are analyzed and compared, and the illumination-independent edge detection formula insensitive to illumination variation is presented. Then, for increasing the difference between edges, background and noise, the fuzzy enhancement operator which takes not only the wavelet module magnitude into account, but also the wavelet gradient direction is designed. Finally, single pixel edges are taken out of images according to edge pixels’ characteristic after wavelet transform. Through synthetic and real images experiments, this edge detection method’s performance for the non-uniform weak illumination images is analyzed and compared with other two edge detection methods quantitatively and qualitatively. The experiment result proves the edge detection method works well for the uneven gray and low contrast images.