From: utzoo!decvax!decwrl!turtleva!ken Newsgroups: net.graphics Title: Re: resolution questions Article-I.D.: turtleva.135 Posted: Wed Jan 26 22:29:41 1983 Received: Sun Jan 30 00:49:52 1983 References: ucf-cs.842 The question was at what point one can get good print quality. I take it this means fonts, although lines were mentioned in the original article. I don't know too much about printers, but I have had a lot of experience with video. What is your definition of quality? How do you measure it? What sort of things are most disturbing to you about print at 512x512? The things most disturbing to me are the ragged/jagged edges, otherwise known as aliasing (in the sampling theorem sense). Certainly increasing the resolution to 4Kx4K reduces the jaggedness, but does not eliminate it completely. To eliminate the aliasing (jaggedness) completely, one must resort to anti-aliasing techniques (aptly named!). When you draw lines, circles, or splines, you are sampling a continuous mathematical function at regularly spaced points on a rectangular grid, so sampling theory must be taken into account. Sampling theory says that you damn well better low-pass-filter your signal before you sample it, lest you get aliasing. Aliasing occurs because you round the location of an edge to the nearest pixel. One can move the apparent location of an edge between pixels by diminishing the intensity: Anti-aliasing techniques trade off amplitude (brightness) for phase (location), resulting in a shift in the apparent position of an edge. I used antialiasing techniques to render fonts, lines, and polygons when I was a member of the engineering staff of a broadcast quality video art system (AVA) a few years ago. The frame store resolution was 768x486x8, and we got great looking characters. The quality was so good, that even characters *3 pixels high* were readable, as long as they were upper case and well separated. 6 pixel characters were good, and 10 pixel characters were excellent, especially compared with 3. The more bits per pixel that one has, the more one can get rid of the aliasing. The biggest jump in quality was from 1 to 2 bits per pixel, although we generally used 4 (for intensity; the other 4 were used for tint). Anti-aliasing tends to smooth out edges at the expense of making edges look softer. Increasing the resolution will make edges sharper; 3 pixel high characters will still be as readable as at lower resolutions. Ken Turkowski (turtlevax!ken) [1] Crow, F.C. A comparison of antialiasing techniques. IEEE Comput. Gr. Appl. v.1 no.1 (Jan. 1981) pp. 40-48 [2] Turkowski, K. Anti-Aliasing through the use of coordinate transformations. ACM Tr. Graphics, v.1 no.3 (July 1982) pp.213-234