Detect Local Minima of a histogram
in [Matlab]
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From: Tessa on 16 Mar 2010 02:24 I am now working on a histogram of an image, is anyone has any idea how to detect local maxima and local minima of a histogram? Appreciate your help. Urgent.
From: Walter Roberson on 16 Mar 2010 02:49 Tessa wrote: > I am now working on a histogram of an image, is anyone has any idea > how to detect local maxima and local minima of a histogram? Appreciate > your help. Urgent. Local maxima: the value is greater than both the previous value and the next value. Local minima: the value is less than both the previous value and the next value. These definitions have a small problem if there are equal adjacent values: if you have (say) 4 2 2 2 5, then _which_ of the 2's is the local minima? I seem to recall that recently John D'Errico mentioned something about a FEX contribution that took a gradient-based approach to this matter. I haven't looked at his code, but I would -speculate- that it knows how to ignore small local minima that are part of a downward trend.
From: Tessa on 16 Mar 2010 03:11 On Mar 16, 2:49 pm, Walter Roberson <rober...(a)hushmail.com> wrote: > Tessa wrote: > > I am now working on a histogram of an image, is anyone has any idea > > how to detect local maxima and local minima of a histogram? Appreciate > > your help. Urgent. > > Local maxima: the value is greater than both the previous value and the > next value. > > Local minima: the value is less than both the previous value and the > next value. > > These definitions have a small problem if there are equal adjacent > values: if you have (say) 4 2 2 2 5, then _which_ of the 2's is the > local minima? > > I seem to recall that recently John D'Errico mentioned something about a > FEX contribution that took a gradient-based approach to this matter. I > haven't looked at his code, but I would -speculate- that it knows how to > ignore small local minima that are part of a downward trend. Thank you for your sharing. Let's say if a histogram is ideal, it has some peaks(maxima) and troughs(minima), however, there are still some noises from the diagram, if there are only 3 peaks and 3 troughs, but due to noise the algorithm can detect more than that, which means i need to either smooth the histogram first, or I need filter those noises to get the outcome that I want. After I detect them, I need to plot them on the original histogram as well. Thank you again.
From: ImageAnalyst on 16 Mar 2010 06:22 Sometimes I've run my histogram through a median filter to smooth it a bit so that I can try to select a proper threshold. Perhaps you can try that.
From: Tessa on 16 Mar 2010 20:35
On Mar 16, 6:22 pm, ImageAnalyst <imageanal...(a)mailinator.com> wrote: > Sometimes I've run my histogram through a median filter to smooth it a > bit so that I can try to select a proper threshold. Perhaps you can > try that. Would you mind to show me how do you do that? |