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Where is the error in this DCT-approach? [message #68411]

Tue, 27 October 2009 14:02

rogass
Messages: 200
Registered: April 2008

Senior Member

Hi there,
I cant find the error in this little program to compute forward and
backward the discrete cosine transform of an image. It seems to be
also difficult to avoid the loops. Please help me. Here is the code:

function cr_dct,dat,mode,shiftit=shiftit

sz = size(dat,/dimensions)
dim = n_elements(sz)
mode = n_elements(mode) eq 0? -1 : -2>mode<2
shiftit = keyword_set(shiftit)? 1 : 0

case dim of

1 : begin

end
2: begin
x = sz[0]
y = sz[1]
c = fltarr(sz)
sqrtx = sqrt(x)
sqrty = sqrt(y)
sqrt2 = sqrt(2)
sqrt2x = sqrt2/sqrtx
sqrt2y = sqrt2/sqrty
arr = c
indarr = (((l=findgen(x>y)))#(2.*l+1))*!dtor
cosxarr = cos(indarr/(2.*x))
cosyarr = x eq y? cosxarr : cos(indarr/(2.*y))
for u=0,x-1 do begin
for v=0,y-1 do begin
alphau = u eq 0 ? sqrtx : sqrt2x
alphav = v eq 0 ? sqrty : sqrt2y
tmparr = arr
;tmparr=dat*((r=rebin(cosxarr[u,*],x,y))) * $
; (x eq y? r: rebin(cosyarr[v,*],x,y))
;tmparr=(dat)[*] * ((r=(rebin(cosxarr[u,*],x,y))[*])) * $
; (x eq y? r : (rebin(cosxarr[v,*],x,y))[*])

for i=0,x-1 do $
for j=0,y-1 do $
tmparr[i,j] = mode eq -1? $
dat[i,j]*cosxarr[u,i]*cosyarr[v,j] : $
alphau*alphav*dat[i,j]*cosxarr[u,i]*cosyarr[v,j]
c[u,v] = mode eq -1? total(tmparr)*alphau*alphav : total(tmparr)

endfor
endfor
c = shiftit? shift(c,long(x/2),long(y/2)) : c

end

endcase
print,mode
return,c
end

pro test_dct
test=dist(16)
tvscl,congrid(test,128,128),0
tvscl, congrid(cr_dct(cr_dct(test,-1,/shiftit),1,/shiftit),128,128) ,1
end

Thank you and best regards

CR

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[Message index]

		Where is the error in this DCT-approach? By: rogass on Tue, 27 October 2009 14:02
		Re: Where is the error in this DCT-approach? By: rogass on Tue, 03 November 2009 02:36
		Re: Where is the error in this DCT-approach? By: penteado on Mon, 02 November 2009 15:44
		Re: Where is the error in this DCT-approach? By: rogass on Mon, 02 November 2009 15:27

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