| Re: about label_region [message #25682 is a reply to message #25610] |
Wed, 11 July 2001 04:25  |
Martin Downing
Messages: 136
Registered: September 1998
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Senior Member |
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Julia,
The algorithm will be written in C as it requires a raster search through
the image for connected blobs. I cant find a reference right now but it goes
something like this psuedo code (considering the raster order to be left to
right working through rows down to up):
-------------------------------------
label _image, IMAGE
create a long image LAB_IM for output
for each pixel:
;check IMAGE to see if background pixel
if background then continue
; else check LAB_IMAGE for connectivity and labelling
if connected to labelled pixel BELOW or LEFT (also BELOW-LEFT,
BELOW-RIGHT if 8 connected) then begin
if connected to more than one label add label pairs to an equivalent
list, ie [1,5] means LABEL 1 = = LABEL 5
assign (first) label to pixel in lab_image
else assign new label to pixel in lab_image
endfor
use equivalent list to create a lookup table reducing all used labels to a
unique set starting from 1
now run through label image replacing each label with its reduced value
----------------------------------------------------
hope this make some sense
Martin
--
----------------------------------------
Mr. Martin Downing,
Clinical Research Physicist,
Orthopaedic RSA Research Centre,
Woodend Hospital,
Aberdeen, AB15 6LS.
"Julia" <julia65201@usa.net> wrote in message
news:f5bebc4d.0107100654.5c89f298@posting.google.com...
>> Amar Nayegandhi said,
>> [
>> label_region uses a 'connected components' algorithm that is described
>> in any good Image Processing text book. It has the option of using 4
>> neighbors or 8 neighbors. I have used labe_region often, and I have a
>> strong feeling i get the same results using the 4 or 8-neighbor
>> approach. I dont think the 8-neighbor approach gives any better results
>> than the 4-neighbor approach.
>> - amar
>> ]
>
> Thanks for your information!
>
> I just wonder where IDL put all these functions in. Is it written in
> IDL or C? I tried to realized it in IDL. As you know, since
> connectivity algorithm is not a parallel algorithm, it should be done
> on pixels one by one. And to keep the equivalent region information, I
> assign a very big matrix even it is very sparse. So the algorithm is
> very slow. Can you give me some hint to improve it, such as how to
> keep the equivalent region information efficiently?
>
> Julia
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