A waveform monitor for generating a modified image from an original image includes a measuring system to select luminance frequency values of the original image that are above a first and a second threshold. A modifier changes selected pixels of the original image that fall above the first and second thresholds. In some embodiments these changed pixels are given a false color as color markers to indicate DOF and areas of sharpest focus of the original image. Methods of modifying images in this manner are also described.