otsu threshold in python

Hyuga hyugaricdeau at gmail.com
Wed Jun 6 17:54:28 CEST 2007


On Jun 6, 7:49 am, azrael <jura.gro... at gmail.com> wrote:
> the otsu filter is a filter that takes a image and from its histogram
> calculates the values at which the image should be thresholded to
> acomplish an optimal seperation of a foregtround and background
> object.

So I learned from the PDF I linked you to.  Take a good look at it.
The equation is fairly simple to begin with, and the paper shows how
to simplify the calculation quite a bit.
Also, the Wikipedia article at http://en.wikipedia.org/wiki/Otsu's_method
even gives a simple pseudo-code implementation.  I've tried it myself
in Python, and it seems give good results.

> I didn't hear about, but I used it through the ImageJ tool. It gave me
> optimal results. I'm working on a project for my clases, and the last
> thing I need to accomplish my goal is this filter. Is there anyone who
> implemented it.
>
> Thanks Hyuga
>
> On Jun 5, 6:02 pm, Hyuga <hyugaricd... at gmail.com> wrote:
>
> > On Jun 5, 10:19 am, azrael <jura.gro... at gmail.com> wrote:
>
> > > Hy guys.
> > > I'd like to ask you for a favour.
> > > I tried several times to implement the otsu threshold filter in
> > > python. but I failed every time. I found the soucre code i n Java from
> > > the ImageJ project but I never worked in Java and there have been used
> > > some built in Java functions which I don't know how they behave. I
> > > also found the otsu threshold in the ia636 python module and would
> > > like only this filter and don't want to import this library.
> > > Is there anyone who wold like to help me. I need a function that takes
> > > a list of 256 elements as an argument and returns the threshold values
> > > for the threshold according to Otsu.
>
> > > In addvance, I don't expect someone to do my homework. I really tried
> > > it, I have been googling and didn't find a standalone function. I
> > > wasn't able write a standalone function because I don't understand the
> > > Otsu method. I just know that it works well and that I need it.
>
> > > If there is no one that wants to help me with this problem, can
> > > someone at least explain me in a detailed way how to implement it.
>
> > > Thanks
>
> > What is the whole assignment meant to accomplish?  Is the assignment
> > to implement the Otsu method?  If so, you shouldn't be trying to find
> > library functions.  Or is it just something you need for some larger
> > task?
>
> > I would ask exactly what problems you're running into, but:
>
> > > it, I have been googling and didn't find a standalone function. I
> > > wasn't able write a standalone function because I don't understand the
> > > Otsu method. I just know that it works well and that I need it.
>
> > How do you know you need it?  Did you learn about this in class?  And
> > if so, are you expected to understand it?
> > I've never even heard of it, but I googled it, and found the fourth
> > hit pretty good:http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/MORSE/thresho...
> > This gives a reasonable explanation.  I couldn't tell you *exactly*
> > why it works, but it's understandable enough from that that I can see
> > that it should work, and to see how to implement it.
>
> > Not to mention that the above PDF basically *gives* you the
> > implementation for free (just make sure not to miss the recurrence
> > relations at the end of the section on the Otsu method, or else you'll
> > be screwing yourself).
>
> > So give that a look and see if it helps.
>
> > Hyuga





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