Image Contrast Enhancement

Purposes of Image Contrast Enhancement Enhancements are used to improve the appearance of an image and make it easier for visual interpretation, understanding, and analysis of imagery. There are a variety of point and local image enhancement operations. Point operations modify the DN of each pixel in an image independently, such as contrast stretching; Local operations modify the value of each pixel in the context of its neighborhood like spatial filters; Often, a trial-and-error approach is needed to produce an image that has the right contrast, and highlight the right features. Image Contrast Enhancement Purposes Some basic image enhancement techniques can be used to modify the appearance of images to highlight certain features while suppressing others. The mean, standard deviation, minimum value, maximum value, and histogram of the image DN are often used to statistically characterize digital images. In ENVI, various contrast enhancement methods are available, including simple linear, piecewise linear, histogram equalization, histogram matching, Guassian Equalize, Square-root, Exponential, etc. While there is rationale behind the various approaches, the creation of an easily interpretable image is largely an art and requires trial and error as well as patience.