| Re: Question on watershed segmentation [message #42230 is a reply to message #42229] |
Fri, 14 January 2005 12:07   |
btt
Messages: 345
Registered: December 2000
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Senior Member |
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Karsten Rodenacker wrote:
> On 14 Jan 2005 10:38:53 -0800, Pravesh <praveshsubramanian@yahoo.com>
> wrote:
>
>> has anybody used watershed from the idl lib?
>>
>> When we use watershed, the returned array consists of integers that
>> number the regions that belong together.
>> 0's indicate the boundary of these regions.
>> so, if from a watershed-segmented image, i want to extract data for a
>> particular segment only, how do i do it?
>> the fact that a logical segment in an image can contain a number of
>> segment obtained from watershed should be taken into consideration.
>
>
> That is just the drawback and the advantage of the watershed
> transformation. It is upon you to merge the parts which are distinct
> under watershed following your logics and necessity.
>
>> if the image can be divided into 6 logical segments, how do i get the
>> data(say, no. of pixels) for segment number 3 that consists of say, 500
>> small segments (watersheds!) obtained from watershed function.
>>
> One way to reduce the so called oversegmentation can be the
> preprocessing of the data e.g. by smoothing (gaussian, nlg, opening,
> closing etc) another is to try to merge the segments by certain criteria.
>
Hi,
Even after preprocessing the image, you'll want an effificant means of getting
at the pixels that belong to a region. To get at the pixels that are labeled
with a particular number, try using the HISTOGRAM function with the
REVERSE_INDICES keyword.
segImage = WATERSHED(image)
h = HISTOGRAM(segImage, reverse = rev)
See the HISTOGRAM online help for how to use the rev vector.
Ben
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