| Re: how to create a loop? [message #38480] |
Thu, 11 March 2004 07:34 |
R.G. Stockwell
Messages: 363
Registered: July 1999
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Senior Member |
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"Thomas Nehls" <thomas.nehls@tu-berlin.de> wrote in message news:c2pveg$p24$1@mamenchi.zrz.TU-Berlin.DE...
> Hi,
>
> I want to create a loop, in which an array is filled pixel by pixel.
> Like this a(n) = a(n-1) + C*d
>
> I tried this
>
> new = indgen(3,400,400)
> runner= indgen(3,400,400)
>
> FOR g= 0,255 DO BEGIN
> grey = imageA[2,*,*] eq g ; so grey is my mask, containing the greylevel
>
> FOR j=0,2 DO BEGIN
> new[j,*,*] = runner[j,*,*] + imageB[j,*,*]*grey ; Image B contains
> the colors I want to employ
> new = runner
> ENDFOR
> ENDFOR
>
> My questions: (i)is the runner appropriate to do what I want or are
> there better ways to do this?
> (ii) is the "+" the right way to fill the array pixel by pixel?
>
> The results were not very exciting, I got a grey diagonal striped image...
> Thank you very much
> Tom
>
Hi Tom,
your line of new = runner is merely erasing any results,
and the equivalent of what you are doing in the lines above
can be written much shorter as follows:
runner= indgen(3,400,400)
So yes, you get a diagonal striped image in runner.
Other than that I'm not sure what you are trying to do.
To fill an array "Like this a(n) = a(n-1) + C*d"
; fist allocate "a" of size "npoints"
a = fltarr(npoints)
a[0] = c*d ; guessing a starting point
for i =1,npoints-1 do begin
a[i] = a[i-1] + c*d
endfor
This could (should!) be vectorized which would be
much quicker, but perhaps that is a later lesson.
Cheers,
bob
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