An Image Quality Metric for Digital Letterforms

Abstract

Alphanumeric characters often appear distorted when displayed on cathode ray tube devices. These image distortions, referred to as "jaggies", result from undersampling the original high-resolution versions of the characters. To eliminate the aliasing errors that result from undersampling an image, one can filter out frequencies greater than the Nyquist limit - however practical limitation of the display device (gaussian pixel profile and limited intensity range) make the filtering less than ideal. (Kajiya, 1981) Additional image distortions occur because of a mismatch between the filters used to sample a high-resolution image (referred to as convolution kernels) and the pixel point-spread function of the monitor used to display the sampled and filtered image (referred to as the reconstruction kernel).