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Re: Chunk Array Decimation [message #63719 is a reply to message #32363]

Tue, 18 November 2008 02:52

Wout De Nolf
Messages: 194
Registered: October 2008

Senior Member

On Mon, 17 Nov 2008 13:40:45 -0800 (PST), Keflavich
<keflavich@gmail.com> wrote:

> Does anyone know how to implement this algorithm using a median
> stack of each pixel instead of simply adding / averaging?

The 'dual histogram loop' approach to drizzling, which you use, loops
over the index-frequencies and not over the index-values like e.g. the
'single histogram' loop does. In the first case, intermediate results
(partial sums) are calculated each iteration while in the second case,
final results (total sums) are calculated each iteration.

As far as I know, there is no 'intermediate' median (i.e. the
equivalent to a partial sum). So maybe the single histogram loop is
what you need:

data=[1,2,3,4,5]
inds=[4,4,1,2,1]

mx=max(inds)
vec3=fltarr(mx+1)
h=histogram(inds,reverse_indices=ri,OMIN=om)
for j=0L,n_elements(h)-1 do if ri[j+1] gt ri[j] then $
vec3[j+om]=median(data[ri[ri[j]:ri[j+1]-1]])

Does this help?

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[Message index]

		Chunk Array Decimation By: JD Smith on Tue, 01 October 2002 12:32
		Re: Chunk Array Decimation By: JD Smith on Fri, 04 October 2002 15:07
		Re: Chunk Array Decimation By: Jaco van Gorkom on Mon, 07 October 2002 08:51
		Re: Chunk Array Decimation By: JD Smith on Wed, 09 October 2002 17:18
		Re: Chunk Array Decimation By: JD Smith on Wed, 09 October 2002 17:19
		Re: Chunk Array Decimation By: Jaco van Gorkom on Thu, 10 October 2002 07:26
		Re: Chunk Array Decimation By: JD Smith on Thu, 10 October 2002 11:51
		Re: Chunk Array Decimation By: Keflavich on Tue, 18 November 2008 07:21
		Re: Chunk Array Decimation By: Wout De Nolf on Tue, 18 November 2008 02:52
		Re: Chunk Array Decimation By: Keflavich on Mon, 17 November 2008 13:40

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