Abstract:

For the defects that the image can only be decomposed into a finite orientation by the wavelet transformation, and multidirectional of image can not be better characterized, the directional filter is applied to the method of wavelet threshold, namely, the HWD(Hybrid WaveletDirectional filter banks) instead of the mere wavelet transform is used to better characterized the multi-directional of image and to retain more image information. To avoid the phenomenon of amplitude cross exists between image wavelet coefficients and noise wavelet coefficients, the method of wavelet thresholding was restricted by this shortcoming, membership function was changed based on the principle of the wavelet, and the membership weights of HWD was built by the membership function. The wavelet coefficients of noise were set to zero maximum with losing the image coefficients at least by this improved HWD. The wavelet coefficients of noise were set to zero maximum with losing the image coefficients at least by this improved HWD. The studies show that more details of engineering drawings can be retained by the improved wavelet threshold method beside removing some noise.

Key words: wavelet transform, directional filter, wavelet thresholding algorithm, engineering drawings denoising