ON ALIASING EFFECTS IN THE CONTOURLET FILTER BANK

The pyramidal directional filter bank (PDFB) for the con-tourlet transform is analyzed in this paper. First, the PDFB is viewed as an overcomplete filter bank, and the directional filters are expressed in terms of polyphase components of the pyramidal filter bank and the conventional DFB. The alias-ing effect of the conventional DFB and the Laplacian pyra-mid to the equivalent directional filters is then considered, and the conditions to reduce this effect are presented. Ex-periments show that the designed PDFBs satisfying these re-quirements have the equivalent filters with much better fre-quency responses. The performance of the new PDFB is ver-ified by non-linear approximation of images. It is found that improvement of 0.2 to 0.5 dB in PSNR as compared to the existing PDFB can be achieved. 1