where T is a grayscale transformation that specifies the mapping between the input image f and the result g, and i,j denotes the row, column index of the pixel. Point operations are a one-to-one mapping between the original (input) and modified (output) images according to some function defining the transformation T.
OK. So what does that have to do with us? Point operations can be used to enhance an image. Details not clearly visible in the original image may become visible upon the application of a point operator. For example, a dark region in an image may become brighter after the operation.