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Re: Chunk Array Decimation [message #63709 is a reply to message #32363]

Tue, 18 November 2008 07:21

Keflavich
Messages: 19
Registered: May 2008

Junior Member

On Nov 18, 3:52 am, Wox <s...@nomail.com> wrote:
> On Mon, 17 Nov 2008 13:40:45 -0800 (PST), Keflavich
>
> <keflav...@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?

It does, thanks. That's remarkably simple; I think it's time for me
to understand reverse indices on a deeper level.

Adam

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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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