By the way, Cliff Reiter's median in J isn't slow at all, for example compared to famous software like ImageMagick:
$ time convert -median 3x3 p19.pgm m3.pgm real 0m11.961s user 0m22.333s sys 0m0.292s $ $ time convert -median 13x13 p19.pgm m13.pgm real 1m13.204s user 2m22.517s sys 0m0.352s Good old xv uses 10s resp. 5 minutes. Ben ________________________________________ From: [email protected] [[email protected]] on behalf of Ben Gorte - CITG [[email protected]] Sent: Wednesday, April 24, 2013 15:47 To: [email protected] Subject: Re: [Jchat] J for Image Processing 6!:2 'med3 =: 3 medianf p19' 17.9526 6!:2 'med13 =: 13 medianf p19' 47.2474 $p19 3072 4608 (A median 3x3 median filter on a 3072x4608 image takes 18s, and a 13x13 median takes 47s). This is on an Intel Core 2 Duo CPU at 2.00GHz , using the median function from the already-mentioned book of Cliff Reiter "Fractals, Visualization and J": medianf =: 1 : '(2#m) "_ (<.-:*:m)&{@:(/:~)@,;._3 ]' I have a C program doing the same in 0.7s resp. 1.2s, but when I consider how much time it took me to write that one, I must compute an awful lot of medians with it before earning back that time. Ben ________________________________________ From: [email protected] [[email protected]] on behalf of Sarah Arnold [[email protected]] Sent: Wednesday, April 24, 2013 15:02 To: [email protected] Subject: Re: [Jchat] J for Image Processing Hi I should have been a bit more precise: I'm into astronomy. I'm mostly interested in noise reduction / signal enhancement and therefore apply different filters to the image. Some of this operations, like for example the MedianFilter[] function, take a lot of computation time. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
