1. A method for generating a display image from a source image, comprising: receiving, on a processor-based system, a selection of a visual characteristic exhibited by a pixel or group of pixels present in the source image or in a palette displayed on a screen of the processor-based system; and applying an effect to a region of the source image to generate the display image, wherein applying the effect comprises modifying the visual appearance, when displayed, of a plurality of eligible pixels that exhibit the visual characteristic and are within the region of the source image, wherein the extent to which the visual appearance of a respective pixel of the plurality of eligible pixels is modified is a function of the location of the respective pixel within the region and the extent to which the respective pixel possesses the visual characteristic and wherein the effect is applied without detecting an edge within the region of the source image.