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thresholding image [message #91447]

Thu, 16 July 2015 04:09

Shaktivel Pillai
Messages: 16
Registered: June 2015

Junior Member

What does a threshold value does to an image.
I mean if choose a particular intensity value as threshold value and if apply the threshold value to the image,
What does the threshold value make changes in the image
for example..
I have an image with min and max value of intensity as x1 and y1.
A particular region in that image has min and max intensity values as a1 and b1.
If I only want to highlight the particular region I need to apply a threshold value to the entire image.
So can one guide me out on how and on what basis to choose the threshold value for this image..
thanks

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Re: thresholding image [message #91458 is a reply to message #91447]

Thu, 16 July 2015 11:58

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Thursday, July 16, 2015 at 7:09:34 AM UTC-4, SP wrote:
> What does a threshold value does to an image.
> I mean if choose a particular intensity value as threshold value and if apply the threshold value to the image,
> What does the threshold value make changes in the image
> for example..
> I have an image with min and max value of intensity as x1 and y1.
> A particular region in that image has min and max intensity values as a1 and b1.
> If I only want to highlight the particular region I need to apply a threshold value to the entire image.
> So can one guide me out on how and on what basis to choose the threshold value for this image..
> thanks

It's probably best to start with an internet search for image thresholding. There are lots of good resources on-line already.

As for how to choose the threshold value... well that depends on what you are trying to achieve. It's not always an easy choice. You may have to do statistical analysis on the image, or have other information from different sources which informs your decision.

CM

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Re: thresholding image [message #91463 is a reply to message #91458]

Thu, 16 July 2015 16:47

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Craig Markwardt writes:

> It's probably best to start with an internet search for image thresholding. There are lots of good resources on-line already.
>
> As for how to choose the threshold value... well that depends on what you are trying to achieve. It's not always an easy choice. You may have to do statistical analysis on the image, or have other information from different sources which informs your decision.

cgStretch from the Coyote Library will allow you to see a histogram of
your image and apply the threshold interactively. It is a good way to
explore your image data and see the results of various threshold values.

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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