Thresholding is the most widely used technique for

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Unformatted text preview: g is the most widely used technique for segmentation in industrial vision applications. The reasons are that it is fast and easily implemented and that the lighting is usually controllable in an industrial setting. Once thresholding is established for a particular image, the next step is to identify particular areas associated with objects within the image. Such regions usually possess uniform pixel properties computed over the area. If objects do not touch each other, and if their gray levels are clearly distinct from background gray levels, thresholding is a suitable segmentation method. Correct threshold selection is crucial for successful threshold segmentation; this selection can be determined interactively or it can be the result of some threshold detection method. Only under very unusual circumstances can thresholding be successful using a single threshold for the whole image (global thresholding) since even in very simple images there are likely to be gray level variations in objects and background; this variation may be due to non uniform lighting or non uniform input device parameters or a number of other factors. Segmentation using variable thresholds (also called adaptive thresholding), in which the threshold value varies over the image as a function of local image characteristics, can produce the solution in these cases. Basic thresholding has many modifications. One possibility is to segment an image into regions of pixels with gray-levels from a set D and into background otherwise (band thresholding): Can be useful in microscopic blood cell segmentations. Can serve as a border detector as well, assuming dark objects on alight background, some gray-levels between those of objects and background can be found only in object borders. There are many modifications that use multiple thresholds, after which the resulting image is no longer binary, but rather an image consisting of a very limited set of gray levels. Another special choice of gray-level subsets Di defines semi thresholding, which is sometimes used to make human assisted analysis easier. This proces...
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