Contrast manipulation

Abstract

This chapter presents the most common pointwise operations in image processing: brightness and contrast adjustment, digital negative, linear contrast stretching and histogram equalization. Pointwise operations are the most simple operations that can be performed on an image, where each value of the output image depends only on the correspondent value of the input image. These operations are usually applied in order to improve the quality of the images, which can be analyzed using R through statistical and graphical information obtained from the image data. This is possible because once the image is read inside R using one of the functions presented in the previous chapter, the image becomes a matrix of values just like any other data set. Information such as minimum, maximum, mean, median and quantiles can be calculated directly from this data. Besides, graphics that guide the analysis such as pairs, 3D perspectives, boxplots and histograms can be built to visualize the data. The operations can be applied easily using R as it is presented throughout the chapter by different examples.