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Anti-Vignetting
In order to correct the effects of nonuniform illumination in a digital image, the background brightness can be measured at a number of points and used to generate a background using a polynomial function. A simplified form of the polynomial adjustment technique that is particularly suited to correcting for vignetting adds brightness to the image in a radially symmetrical pattern, with an adjustable amount and a power that varies between the square and the cube of the radius, as shown in the following interactive tutorial. This interactive tutorial illustrates the correction of vignetting by the addition of brightness using a power-law function.
The tutorial initializes with a randomly selected specimen imaged in the microscope appearing in the left-hand window entitled Specimen Image. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. Adjacent to the Specimen Image window is the Corrected Image window that displays the result of applying the power-law function to the Specimen Image. The sliders control the shape of the function. The Amount slider adjusts the magnitude of the addition, while the Power slider varies the shape from the square to the cube of radial distance from the center.
Contributing Authors
John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.
Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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