TAILIEUCHUNG - The Essential Guide to Image Processing- P27

The Essential Guide to Image Processing- P27:We are in the middle of an exciting period of time in the field of image processing. Indeed, scarcely a week passes where we do not hear an announcement of some new technological breakthrough in the areas of digital computation and telecommunication. | 792 CHAPTER 27 Computer-Assisted Microscopy This is particularly true for the microscope system. Both the halogen transmitted light and mercury fluorescence light lamps have to be adjusted for uniform illumination of the FOV prior to use. Moreover microscope optics and or cameras may also show vignetting in which the corners of the image are darker than the center because the light is partially absorbed. The process of eliminating these defects by application of image processing to facilitate object segmentation or to obtain accurate quantitative measurements is known as background correction or background flattening. Background Subtraction For microscopy applications there are two approaches that are popular for background flattening 30 . In the first approach a background image is acquired in which a uniform reference surface or specimen is inserted in place of actual samples to be viewed and an image of the FOV is recorded. This is the background image and it represents the intensity variations that occur without a specimen in the light path only due to any inhomogeneity in illumination source the system optics or camera and can then be used to correct all subsequent images. When the background image is subtracted from a given image areas that are similar to the background will be replaced with values close to the mean background intensity. The process is called background subtraction and is applied to flatten or even out the background intensity variations in a microscope image. It should be noted that if the camera is logarithmic with a gamma of then the background image should be subtracted. However if the camera is linear then the acquired image should be divided by the background image. Background subtraction can be used to produce a flat background and compensate for nonuniform lighting nonuniform camera response or minor optic artifacts such as dust specks that mar the background of images captured from a microscope . In the process of .

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