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Re: checking for connectedness of a given set of pixels [message #74182 is a reply to message #73514]

Mon, 03 January 2011 13:50

guillermo.castilla.ca is currently offline

guillermo.castilla.ca
Messages: 27
Registered: September 2008

Junior Member

On Nov 14 2010, 5:56 pm, Guillermo
<guillermo.castilla.castell...@gmail.com> wrote:

> ...REGI0N_GROW that may be faster than
> LABEL_REGION for this purpose when the minimum bounding box for the
> input set of pixels is large. I have modified your function to include
> the former as an alternative method (below). I'll do some tests and
> report back (hopefully within this year :).

Just for the record, today I made a test with a 50 megapixel labeled
image derived from the rasterization of a polygon vector layer
containing 185 elongated features (rivers), of which 65 ended up
consisting of disconnected groups of pixels. Checking for
connectedness of the pixels within each feature took almost 3 times
more using the REGI0N_GROW method than using LABEL_REGION (the latter
taking in average 30 millisecs per feature). I quickly looked into the
REGI0N_GROW code and noticed that it is based on LABEL_REGION itself,
so no wonder. Repeated the test with SEARCH2D instead of REGI0N_GROW
and although it was two times faster than the latter, it was still
slower than LABEL_REGION. So it looks like LABEL_REGION, even if it
does a lot of unnecessary extra work for this task, is the method of
choice for checking for connectedness of a set of pixels.

Happy new year!

Guillermo

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[Message index]

		Re: checking for connectedness of a given set of pixels By: David Fanning on Wed, 03 November 2010 06:35
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Wed, 03 November 2010 06:32
		Re: checking for connectedness of a given set of pixels By: David Fanning on Tue, 02 November 2010 15:14
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Tue, 02 November 2010 15:06
		Re: checking for connectedness of a given set of pixels By: David Fanning on Tue, 02 November 2010 13:37
		Re: checking for connectedness of a given set of pixels By: James[2] on Mon, 08 November 2010 11:22
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Sun, 14 November 2010 13:56
		Re: checking for connectedness of a given set of pixels By: guillermo.castilla.ca on Mon, 03 January 2011 13:50

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