Re: Dereferencing a Pointer Array

[Art Burden <aburden(at)mpl.ucsd.edu>]

Thanks Liam, that worked beautifully.  I knew I was making this complicated..
Sometimes it's easy to use the routines blindly without thinking about how
they are defined (such as, mean = sum/num)

"Liam E. Gumley" wrote:

> Art Burden wrote:
> > I have a structure that contains a pointer array that points to twelve
> > 512-by-512 images.  I would like to find the mean image from the twelve
> > images in a simple and fast way.  I understand that I can dereference
> > the pointer to an image or an individual element in an image by using,
> > for example
> >
> > img = (*info.images[0])
> > and
> > img_element = (*info.images[0])[240,240]
> >
> > but I can't figure out a way to dereference the pointers to all 12 pixel
> > values from a given coordinate in one step.  At this stage, I pass the
> > structure into my averaging subroutine and  I create a new array to
> > store the 12 images. I then fill the array by dereferencing the pointer
> > to each image in a loop.  Finally, I  loop through the rows and columns
> > to get each mean pixel value, as shown below.  Can anyone think of a
> > better (mainly faster) way to do this?
> >
> > ;retrieve array of images
> > ffim = lonarr(12,512,512)
> > for num=0,11 do ffim[num,*,*] = *info.images[num]
> >
> > ;calculate mean of images
> > mean_ff = fltarr(512,512)
> > for ir = 0,511 do for ic = 0,511 do mean_im[ic,ir] = mean(ffim[*,ic,ir])
>
> Perhaps something like this (untested):
>
> sum = fltarr(512, 512)
> n = 12
> for i = 0L, n - 1L do sum = sum + *info.images[i]
> avg = sum / float(n)
>
> Cheers,
> Liam.
> http://cimss.ssec.wisc.edu/~gumley/