ABSTRACT
This chapter argues that a number of image-enhancing transformations can be performed using elementary means, such as linear, piecewise-linear, power, exponential, and logarithmic functions. It shows how even the simplest elementary functions studied in algebra and pre-calculus courses can help us achieve remarkable results in our endeavor of restoring old photos. However, selecting the values of parameters in power, exponential, and logarithmic functions involved in the process of image enhancement was left to trial and error. A well-known class of functions that are concave up is the class of exponential functions. However, the exponential transform tends to be more effective in correcting overexposed images that have most of the pixel values crowded in a small interval near the maximal intensity. Unlike the graphs of the power functions, the graphs of the logarithmic functions do not pass through the origin.
