Otsu's method

From Wikipedia, the free encyclopedia

You have new messages (last change).

The introduction to this article provides insufficient context for those unfamiliar with the subject matter.
Please help Wikipedia by improving the introduction according to the guidelines laid out at Wikipedia:Guide to layout. You can discuss the issue on the talk page.

Otsu's method or Otsu's algorithm or Ad-hoc algorithm is used in computer vision and medical image processing to perform thresholding. It designed to separate foreground from background.

If each pixel p of an image has been assigned an 'interest' (or number of occurrences) score, f(p) then Otsu creates a histogram of f over the image; and selects a threshold to maximize the between-class variance. The method is non-iterative and relies on the assumption that all image pixels belong to one of two classes, background or foreground (i.e. object(s)).

The method was originally described in: N. Otsu, “A threshold selection method from gray-level histograms,” IEEE Trans. Sys., Man., Cyber., vol. 9, pp. 62–66, 1979.

[edit] Otsu's Method Interpretation

 Step through all intensity levels in histogram
   Set T (between-class threshold) to current intensity level
   Compute between-class variance (e.g. derived from zeroth and first order cumulative moments of the histogram, on each side of current level)
 Otsu threshold level is that for which between-class variance is maximum

[edit] Pseudo-code implementation

FG = Foreground, BG = Background, FGregion = Foreground Region, BGregion = Background Region, T = Threshold

Initialise FGregion & BGregion (BGregion is usually the four corners of an image).
While T remains unchanged.
  Find the mean intensity of each region.
  T = ( Fmean + Bmean ) / 2.
  Recalculate the regions:
    FGregion = pixels that their intensity is >= to T.
    BGregion = pixels that their intensity is < to T.


Comp Sci logo This computer science-related article is a stub. You can help Wikipedia by expanding it.
Retrieved from "http://en.wikipedia.org../../../o/t/s/Otsu%27s_method.html"