K.J. Parker¹, T. Mitsa¹ and R.A. Ulichney²,

 ¹Rochester Center for Medical Ultrasound, University of Rochester, Rochester, NY 14627 and ²Image Processing Research Group, Digital Equipment Corporation, Hudson, MA 01749.

Digital halftoning, also referred to as dithering, is the method of rendering the illusion of continuous-tone images on displays and printers that are only capable of producing binary (black or white) picture elements. It can be shown that a dispersed pattern of black and white elements that have spatial power spectra corresponding to blue noise, or a high frequency white noise, have visually pleasing properties including grid defiance. We show that medical ultrasound images are particularly well suited to blue noise halftoning. First, the physics of B-scan imaging of tissues results in speckle and other patterns characterized by high spatial frequencies, which partially mask the dither pattern. Also, some ultrasound video images are subsampled to fit fairly low-resolution grids. In contrast, dithering permits printout of images onto conventional 300 dot per inch laser printers, where full resolution 2K² images fit conveniently onto a standard page along with text. Examples of medical ultrasound images are presented to compare conventional gray scale against dithered, laser-printed images. Issues concerning filtering, implementation, and algorithms will be discussed.

This work was supported in part by the Sponsored Research Program of Digital Equipment Corporation.