Hi, I observed 2 bugs in imtranslate.m from the 'image' package. They are both described below
============== 1st bug ======================================== function Y = imtranslate(X, x_shift, y_shift, bbox_in) suppose to shift/translate image but if (x_shift+y_shift) is odd the resulting image get multiplied by -1. Here is the test: octave:103> it=ones(3) it = 1 1 1 1 1 1 1 1 1 % below correct behavior octave:104> im_sm_trsl=imtranslate(it, 1, 1) im_sm_trsl = 1 1 1 1 1 1 1 1 1 %now incorrect behavior octave:110> it=ones(4) it = 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 octave:111> im_sm_trsl=imtranslate(it, 1, 0) im_sm_trsl = -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 %notice -1 sign. === suggested fix: multiply the final result by (-1)^(shift_x+shift_y) ============== 2nd bug ======================================== Severe precision drop for small images: octave:112> it=ones(3) it = 1 1 1 1 1 1 1 1 1 octave:113> im_sm_trsl=imtranslate(it, 2, 0) im_sm_trsl = -0.50000 -0.50000 -0.50000 -0.50000 -0.50000 -0.50000 -0.50000 -0.50000 -0.50000 # instead of resulting matrix ones we get negative 1/2. ============ Looks like problem is actually in the fft which used for translation, since imtranslate algorithm seems to be correct one. But I do not see an easy fix for second problem. ========================================================================== It is a bit unclear to me why use fft is used for translation. Since integer shift could be done in a simpler way, fractional shift is another story. -- Eugeniy ------------------------------------------------------------------------------ Stay on top of everything new and different, both inside and around Java (TM) technology - register by April 22, and save $200 on the JavaOne (SM) conference, June 2-5, 2009, San Francisco. 300 plus technical and hands-on sessions. Register today. Use priority code J9JMT32. http://p.sf.net/sfu/p _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
