https://bugzilla.wikimedia.org/show_bug.cgi?id=24889
--- Comment #7 from Tim Starling <[email protected]> 2011-12-01 13:12:22 UTC --- Created attachment 9589 --> https://bugzilla.wikimedia.org/attachment.cgi?id=9589 Some frequency spectra A comparison showing the issue in the frequency domain. The left image is the frequency spectrum of the source (VIPS im_fwfft + im_scaleps). Note the strong peaks on the X and Y axes representing the engraving pattern. The middle image has a 10px block average applied, like what VIPS im_shrink uses. Note the notches in the response which suppress part of the engraving pattern. The right image used a 10px radius Gaussian filter like what Brion used in one of his comparison images. Note the circular symmetry in the central area and rapid falloff out of the pass band. If you're reducing the image far enough that the engraving pattern will generate Moire fringes, you need to use a filter which will strongly attenuate the part of the frequency spectrum where the engraving pattern is located. -- Configure bugmail: https://bugzilla.wikimedia.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug. You are on the CC list for the bug. _______________________________________________ Wikibugs-l mailing list [email protected] https://lists.wikimedia.org/mailman/listinfo/wikibugs-l
