| Re: Need hint to use FOR loops using 3-D arrays [message #54400] |
Tue, 12 June 2007 03:43 |
airy.jiang
Messages: 37
Registered: May 2007
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Member |
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On 6 11 , 11 14 , alexcardesin-...@yahoo.com wrote:
> Hi,
>
> I am having a lot of trouble trying to improve a routine that I got
> from a colleague. The goal is to process a 3-D cube removing spikes,
> but it uses three nested FOR loops which makes it amazingly slow. I
> know I should try to remove the single-pix functions and try use the
> array functionalities but I do not manage to do it using a matrix.
>
> Can someone give me a hint?
>
> This is the peace of code:
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> - - -
> ; cube is a tridimensional matrix (256x432x256)
> size_elem=size(cube)
> ns=size_elem[1]
> nb=size_elem[2]
> nl=size_elem[3]
> level=2. ; this is a hardcoded value
>
> tot_pixels=double(ns*nb*nl)
> c1d=0
> c1n=0
>
> ; Evil LOOP
> FOR l=0,nl-1 do begin
> frame=CUBE[*,*,l)
> neighbor=fltarr[9)
> for s=0,ns-1 do begin
> for b=0,nb-1 do begin
> neighbor[0]=frame[s,b]
> neighbor[1]=frame[ 0 > (s-1), b ]
> neighbor[2]=frame[(ns-1) < (s+1), b ]
> neighbor[3]=frame[ s , 0 > (b-1]]
> neighbor[4]=frame[ 0 > [s-1), 0 > (b-1)]
> neighbor[5]=frame[(ns-1) < (s+1), 0 > (b-1)] ; I should
> do this with a matrix, right???
> neighbor[6]=frame[ s ,(nb-1) < (b+1)]
> neighbor[7]=frame[ 0 > (s-1),(nb-1) < (b+1)]
> neighbor[8]=frame[(ns-1) < (s+1),(nb-1) < (b+1)]
> neighbor_sort=neighbor[sort(neighbor)]
> stdev=(neighbor_sort[7]-neighbor_sort[1])/2.
> if (frame[s,b] gt neighbor_sort[4]+level*stdev) or $
> (frame[s,b] lt neighbor_sort[4]-level*stdev) then begin
> cube[s,b,l]=neighbor_sort[4]
> c1d=c1d+1.
> endif
> endfor
> endfor
> endfor
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> - - -
> thanks, alex
Use less array operation,and less nesting.And i agree with Paolo that
using the Shift function.That's my suggestion.I hope it's useful.
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| Re: Need hint to use FOR loops using 3-D arrays [message #54414 is a reply to message #54400] |
Mon, 11 June 2007 08:30  |
Paolo Grigis
Messages: 171
Registered: December 2003
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Senior Member |
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alexcardesin-IDL@yahoo.com wrote:
> Hi,
>
> I am having a lot of trouble trying to improve a routine that I got
> from a colleague. The goal is to process a 3-D cube removing spikes,
> but it uses three nested FOR loops which makes it amazingly slow. I
> know I should try to remove the single-pix functions and try use the
> array functionalities but I do not manage to do it using a matrix.
>
> Can someone give me a hint?
When you are dealing with next neighbours on arrays,
you can use the SHIFT function to get them all at
the same time in one array.
Ciao,
Paolo
>
> This is the peace of code:
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> - - -
> ; cube is a tridimensional matrix (256x432x256)
> size_elem=size(cube)
> ns=size_elem[1]
> nb=size_elem[2]
> nl=size_elem[3]
> level=2. ; this is a hardcoded value
>
> tot_pixels=double(ns*nb*nl)
> c1d=0
> c1n=0
>
> ; Evil LOOP
> FOR l=0,nl-1 do begin
> frame=CUBE[*,*,l)
> neighbor=fltarr[9)
> for s=0,ns-1 do begin
> for b=0,nb-1 do begin
> neighbor[0]=frame[s,b]
> neighbor[1]=frame[ 0 > (s-1), b ]
> neighbor[2]=frame[(ns-1) < (s+1), b ]
> neighbor[3]=frame[ s , 0 > (b-1]]
> neighbor[4]=frame[ 0 > [s-1), 0 > (b-1)]
> neighbor[5]=frame[(ns-1) < (s+1), 0 > (b-1)] ; I should
> do this with a matrix, right???
> neighbor[6]=frame[ s ,(nb-1) < (b+1)]
> neighbor[7]=frame[ 0 > (s-1),(nb-1) < (b+1)]
> neighbor[8]=frame[(ns-1) < (s+1),(nb-1) < (b+1)]
> neighbor_sort=neighbor[sort(neighbor)]
> stdev=(neighbor_sort[7]-neighbor_sort[1])/2.
> if (frame[s,b] gt neighbor_sort[4]+level*stdev) or $
> (frame[s,b] lt neighbor_sort[4]-level*stdev) then begin
> cube[s,b,l]=neighbor_sort[4]
> c1d=c1d+1.
> endif
> endfor
> endfor
> endfor
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> - - -
> thanks, alex
>
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