On Apr 9, 2:50 pm, "R.G. Stockwell" <noem...@please.com> wrote:
>> "Paolo" <pgri...@gmail.com> wrote in message
>> news:929b2d07-c3ce-448e-b36d-0227a031b22e@20g2000vbr.googleg roups.com...
>> On Apr 9, 12:05 pm, "R.G. Stockwell" <noem...@please.com> wrote:
>>> I need to cut an image into 4 equal-size parts, which
>>> obviously is very easy to do in a few lines.
>>> image1 = im[0:nx/2-1, 0:ny/2-1]
>>> image2 = im[0:nx/2-1, ny/2:*]
>>> image3 = im[nx/2:*, 0:ny/2-1]
>>> image4 = im[nx/2:*, ny/2:*]
>
>>> i came across a way to do this with reform, but
>>> it required 4 steps ( several reforms, a couple transposes)
>>> to do it properly.
>
>>> I'd be interested (just for fun) in a vectorized general way to do this
>>> if any of you 'dimension jugglers' have any clever ideas,
>>> for how to take an image and cut it into 4, or 16, or 64,
>>> or 256 equal pieces (that would probably be about the maximum)
>
>> Well, if it is just for fun, why not use a recursive approach?
>> I always like the simplicity of these :) (though they are not
>> always the most efficient way, and sometimes they are the worst
>> way to do it).
>
>> res=segim(dist(512,512),level=4)
>> IDL> help,res
>> RES FLOAT = Array[8192, 32]
>
>> The output is just an array with the images side by side, i.e.
>> [im1,im2,...,im256].
>
>> There are (2^level)^2 subarrays. That is,
>
>> lev =1 -> 4
>> lev =2 -> 16
>> lev =3 -> 64
>> lev =4 -> 256
>> etc.
>
>> Ciao,
>> Paolo
>
>> FUNCTION segim,im,level=level
>
>> IF n_elements(level) EQ 0 THEN level=4
>
>> n=size(im,/dimension)
>> nx=n[0]
>> ny=n[1]
>
>> IF level EQ 0 THEN return,im
>
>> return,[segim(im[0:nx/2-1, 0:ny/2-1],level=level-1),segim(im[0:nx/2-1,
>> ny/2:*],level=level-1), $
>> segim(im[nx/2:* , 0:ny/2-1],level=level-1),segim(im[nx/2:* ,
>> ny/2:*],level=level-1)]
>> END
>
> very nice. I've always been a big fan of recursion. One thing i didn't
> like
> about the recursion approach was that the ordering is a bit awkward,
> especially
> for higher levels. I had originally wanted to start at the top right, and
> go
> left to right, with the ordering.
>
> But as i was looking at this, it occured to me that all i need to
> do is create a latitude array, and a longitude array and segment those as
> well,
> then I can just loop through and process everything in a straightforward
> manner.
>
> I'd just point out that one could do a little juggle to break the arrays out
> with:
> IDL> result2 =
> transpose(reform(transpose(result),nx/(2^level),ny/(2^level) ,(2^(2*level))) ,[1,0,2])
> then the subarrays are
> IDL>print,result2[*,*,0],result2[*,*,1], etc
>
> cheers,
> bob
>
> PS this if for google earth network linking of images, at the varying
> resolutions.
> You know how you zoom in from orbit, all the way down to your house and
> street.
You can get your subdivision indices for any square subdivision
(2x2,3x3,4x4, etc.) pretty easily with two lines of code:
IDL> xy = fix((indgen(n_sub+1)/n_sub)##size(image,/dimensions))
IDL> xy[*,n_sub] -= 1
Then subdivision (2,3) for example is
image[xy[0,2]:xy[0,3],xy[1,3]:xy[1,4]]
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