Hi there,
I have a strange problem with the IDL convolving possibilities. I'd
like to make a script which convolves 2 matrices - e.g. a and b - in
the same behavior conv2(a,b,'same') Matlab does. The Problem is not to
make such a script, the problem is that IDL takes too long or hangs
when i try to convolve larger matrices. I tried certainly all kinds of
using the built-in IDL-convol method, but convolving large arrays ends
always in different results compared to the very fast Matlab conv2.
Maybe someone could help me. Here's the sample code:
function size_dim, in, direction
dims = size(in, /dimensions)
return, dims[direction]
end
function zeropadding, in,xsize,ysize
;only for 2D-arrays
xsize_in=size_dim(in,0)
ysize_in=size_dim(in,1)
shiftx = ceil((xsize-xsize_in)/2)
shifty = ceil((ysize-ysize_in)/2)
temp = fltarr(xsize,ysize)
temp[0:xsize_in-1,0:ysize_in-1] = in
temp = shift(temp,shiftx,shifty)
return, temp
end
function conv2, a,b
size_a=[size_dim(a,0),size_dim(a,1)]
size_b=[size_dim(b,0),size_dim(b,1)]
a=zeropadding(a,size_a[0]+size_b[0], size_a[1]+size_b[1])
b=zeropadding(b,size_a[0]+size_b[0], size_a[1]+size_b[1])
c=fltarr(size_a[0]+size_b[0], size_a[1]+size_b[1], /nozero)
addx = floor(total(size_a)/4)
endx = ceil(double(total(size_a)/4))
addy = floor(total(size_b)/4)
endy = ceil(double(total(size_b)/4))
for n1=0,size_a[0]+size_b[0]-1 do begin
for n2=0,size_a[1]+size_b[1]-1 do begin
temp=0
temp2=0
for k1=0+addx,size_a[0]+size_b[0]-1-endx do begin
for k2=0+addx,size_a[1]+size_b[1]-1-endy do begin
if n1-k1 gt-1 and n2-k2 gt-1 then begin
temp=a[k1,k2]*b[n1-k1+addx,n2-k2+addy]
temp2=temp2+temp
endif
endfor
endfor
c[n1,n2]=temp2
endfor
endfor
temp = shift(c,-2*addx,-2*addy)
return, temp[0:size_a[0]-1,0:size_b[0]-1]
end
pro conv
; sample matrix -> magic(5) in Matlab
a= [[17, 24, 1, 8, 15],$
[23, 5, 7, 14, 16],$
[4, 6, 13, 20, 22],$
[10, 12, 19, 21, 3],$
[11, 18, 25, 2, 9]]
b=2*a
c=a
d=b
print, 'Trying own convolution...',string(10b),conv2(a,b), string(10B)
print, 'Trying built in convolution...',string(10b),$
shift(convol(zeropadding(c,10,10),zeropadding(d,10,10), center=0,/
edge_wrap),-4,-4),string(10b)
end
Maybe there is a solution for using reform in some way? It seems to be
quicker as for-loops. But I can't imagine how it could work when the
indices of the multiplying matrices are varying.
Hope on help
Thank you and best regards
Chris
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