A picture is worth a thousand words, whereas an enhanced image is worth more than that, in terms of clear understanding. The contrast enhancement of images is a need for all time. Newer strategies for enhancing the quality of an image are the most welcome step in understanding and interpreting the image. This book introduces constrained and controlled contrast enhancement techniques for digital images. The well-known meta-heuristic algorithm, Particle Swarm Optimization (PSO) is employed to enhance the input images in a controlled and optimized way.