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Re: Thinning algorithm without for loops [message #55251 is a reply to message #55233]

Thu, 09 August 2007 09:52

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Thu, 09 Aug 2007 01:46:54 +0000, nathan12343 wrote:

> On Aug 8, 3:33 pm, JD Smith <jdsm...@as.arizona.edu> wrote:
>> [quoted text muted]
>
> JD, really elegant way of doing that. I'm still trying to figure out
> what you did with those two rebin commands to resize the pixels that
> passed step 1,

Just some simple rearrangement. I take the list of kept indices,
del=[d1,d2,d3,...], and turn it into an 8xn copy of itself, on its
side:

d1 d1 d1 d1 d1 d1 d1 d1 d1
d2 d2 d2 d2 d2 d2 d2 d2 d2
d3 d3 d3 d3 d3 d3 d3 d3 d3
. . . . . . . . .
. . . . . . . . .

To each row of this, I add a custom offset to index the upper right,
right, lower right, lower, lower left, left, upper left, upper
neighbors. The offset in terms of the single "running" index into the
array (of the type returned by WHERE) is -xs for the row above, +xs
for the row below, +1 to the right, -1 to the left, etc. I take those
eight offsets, call them o1...o8, and simply add them to each row:

o1 o2 o3 o4 o5 o6 o7 o8
o1 o2 o3 o4 o5 o6 o7 o8
o1 o2 o3 o4 o5 o6 o7 o8
. . . . . . . . .
. . . . . . . . .

Add these two together, and you have all 8 neighbors of each of the
d's together in a row.

JD

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[Message index]

		Thinning algorithm without for loops By: nathan12343 on Mon, 06 August 2007 12:31
		Re: Thinning algorithm without for loops By: JD Smith on Thu, 09 August 2007 09:52
		Re: Thinning algorithm without for loops By: nathan12343 on Wed, 08 August 2007 18:46
		Re: Thinning algorithm without for loops By: nathan12343 on Wed, 08 August 2007 10:41

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