When the distribution of a histogram in an image is bi or trimodal, an analyst may stretch certain values of the histogram for increased enhancement in selected areas. This method of contrast enhancement is called a piecewise linear contrast stretch. A piecewise linear contrast enhancement involves the identification of a number of linear enhancement steps that expands the brightness ranges in the modes of the histogram. Figure 6-3.5 shows the logic used in a normal linear contrast stretch compared to a piecewise linear contrast stretch. In the piecewise stretch, a series of small min-max stretches are set up within a single histogram. Because a piecewise linear contrast stretch is a very powerful enhancement procedure, image analysts must be very familar with the modes of the histogram and the features they represent in the real world.