Segmentation (image processing)
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In image analysis, segmentation is the partitioning of a digital image into multiple regions (sets of pixels), according to a given criterion. The goal of segmentation is typically to locate objects of interest and is sometimes considered a computer vision problem. Unfortunately, many important segmentation algorithms are too simple to solve this problem accurately: they compensate for this limitation with their predictability, generality, and efficiency.
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[edit] Pixel based Segmentation
A simple example of this kind of segmentation is thresholding a grayscale image with a fixed threshold t: each pixel p is assigned to one of two classes, P0 or P1, depending on whether I(p) < t or I(p) ≥ t. Some other segmentation algorithms are based on segmenting images into regions of similar texture according to wavelet or Fourier transforms.
Region Merging: quad-tree/oct-tree: a recursive algorithm: the picture is divided into 4/8 parts, if the resulting subpicture doesn´t meet a homogenity criteria, it is further divided, etc. The resulting data structure is a Quadtree/Octree, from which the merging process can be performed.
[edit] Model based Segmentation
by inner forces(ideal: circle) and forces which are computed from the image data, which pull the model towards the object boundary. Statistical Models: if the object to be segmented is known beforehand, a statistical model can be used to serve as a template.
[edit] Multi-scale Segmentation
Image segmentations are computed at multiple scales in scale-space and sometimes propagated from coarse to fine scales; see scale-space segmentation.
Segmentation criteria can be arbitrarily complex and may take into account global as well as local criteria. A common requirement is that each region must be connected in some sense.
[edit] Semi-automatic Segmentation
In this kind of segmentation, the user outlines the region of interest with the mouse clicks and algorithms are applied so that the path that best fits the edge of the image is shown. Techniques like Livewire or Intelligent Scissors are used in this kind of segmentation.
