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Re: STANDARD DEVIATON [message #21049 is a reply to message #20952]

Fri, 04 August 2000 00:00

Struan Gray
Messages: 178
Registered: December 1995

Senior Member

I think this works:

; ************************************

function smg_imageSD, image

fimage = float(image)
localmean = smooth(fimage, 3)
sum = (fimage - localmean)^2
sum = temporary(sum) + $
shift((fimage - shift(localmean, 1, 1))^2,-1,-1)
sum = temporary(sum) + $
shift((fimage - shift(localmean, 0, 1))^2, 0,-1)
sum = temporary(sum) + $
shift((fimage - shift(localmean,-1, 1))^2, 1,-1)
sum = temporary(sum) + $
shift((fimage - shift(localmean, 1, 0))^2,-1, 0)
sum = temporary(sum) + $
shift((fimage - shift(localmean,-1, 0))^2, 1, 0)
sum = temporary(sum) + $
shift((fimage - shift(localmean, 1,-1))^2,-1, 1)
sum = temporary(sum) + $
shift((fimage - shift(localmean, 0,-1))^2, 0, 1)
sum = temporary(sum) + $
shift((fimage - shift(localmean,-1,-1))^2, 1, 1)

sum = sqrt(temporary(sum)/8)

dims = size(sum, /dim)
sum[0,*] = 0.0
sum[*,0] = 0.0
sum[dims(0)-1,*] = 0.0
sum[*,dims(1)-1] = 0.0

return, sum
end

; ************************************

You can generalise the shifting and put it into a double loop over the kernal
indices. You can also deal with edge-effects (and avoid the zeroing of edge
elements) if you creat an oversize image and pad it appropriately. On my
machine this is approx ten times faster than Ben_imageSD.

Struan

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[Message index]

		STANDARD DEVIATON By: Ben Marriage on Tue, 01 August 2000 00:00
		Re: STANDARD DEVIATON By: Struan Gray on Fri, 04 August 2000 00:00
		Re: STANDARD DEVIATON By: Struan Gray on Fri, 04 August 2000 00:00
		Re: STANDARD DEVIATON By: Struan Gray on Fri, 04 August 2000 00:00
		Re: STANDARD DEVIATON By: Ben Marriage on Fri, 04 August 2000 00:00
		Re: STANDARD DEVIATON By: Ben Marriage on Fri, 04 August 2000 00:00
		Re: STANDARD DEVIATON By: Ben Marriage on Mon, 14 August 2000 00:00

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