Many thanks to everybody for your input! J'ers seem to be very well
supported...
On 04/25/2013 11:17 AM, Cliff Reiter wrote:
Hi Bob et al,
In J there is a wonderful conjunction that allows you to apply any
function to all sorts of tessellations of the data. I used u;._3
apparently. I think Sharp APL had a similar thing but I don't know if
that is available in your compiler.
FVJ3 version is
medianf=: 1 : 0
(2#m)"_ (<.-:*:m)&{@:(/:~)@,;._3 ]
)
where
13 medianf g
would apply a 13 by 13 median filter on g. The whole thing is a fork.
(<.-:*:m)&{@:(/:~)@, ravels the patch, orders the data and takes a
datum from the middle (lower choice if even size).
;._3 distributes to tessellations. ] is the identity (g) and (2#m)"_
gives 13 13, the desired size of the tessellation. Very substantial
speed ups are available for multiplicative filters using moving
windows (\ as dyad), but median isn't.
Best, Cliff
On 4/24/2013 2:10 PM, Robert Bernecky wrote:
Hi, Cliff,
I'm looking to turn your medianf function into APL, but
will have to relearn J in order to do so. Can you give me a
quick translation into APLish of that? If that's not trivial,
or if you're up to your butt in alligators, it's no big deal:
I'll dig out the J books and figure it out.
What I want to do is to compile the APL code into
SAC, then compile that and see how well it works in
both serial and parallel environments.
Thanks,
Bob
On 13-04-24 11:01 AM, Cliff Reiter wrote:
In addition to my visualization book (OK fractals) you might look at
preprints of APL quote quad articles
http://webbox.lafayette.edu/~reiterc/j/withj/withj12_im_proc01_pp.pdf
http://webbox.lafayette.edu/~reiterc/j/withj/withj14_im_proc02_pp.pdf
and the vector paper
http://archive.vector.org.uk/art10500860
and ask the forum (or me) if you have questions -- I tend to always
be a couple days out of date on the forum, but I do browse it.
Those books and articles are best used with J6 but I hope that in a
semester or two I will transition to J8.
Best, Cliff
On 4/24/2013 10:32 AM, Sarah Arnold wrote:
Hi Ben
Yes, in mathematica it takes approximately 2 minutes to do the
13x13 medianfilter for a 2004 x 2006 picture... I usually use much
bigger boxsizes (about 120x120), so I can pick up a coffee while
the program is running.
What you write about your use of J sounds promising to me. I
ordered the book from Reiter in the library and will have a look at
it. The tutorials you mentioned: are they somehow available?
Thanks a lot for your answers!
On 04/24/2013 04:14 PM, Ben Gorte - CITG wrote:
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.
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