Xref: utzoo comp.graphics:3548 comp.text:2720 Newsgroups: comp.graphics,comp.text Path: utzoo!utgpu!jarvis.csri.toronto.edu!dgp.toronto.edu!avi From: avi@dgp.toronto.edu (Avi Naiman) Subject: Re: Gray-scale antialiasing (yes, it can work) Message-ID: <8811080140.AA15368@explorer.dgp.toronto.edu> Keywords: grayscale fonts Organization: University of Toronto, CSRI References: <74013@sun.uucp> <148@internal.Apple.COM> <4763@mnetor.UUCP> <174@internal.Apple.COM> <19809@apple.Apple.COM> Date: Mon, 7 Nov 88 20:40:53 EST In article <19809@apple.Apple.COM> jp@Apple.COM (John Peterson) writes: >> David Casseres >> In spite of the enthusiasm of its supporters, the question of the >> *readability* of anti-aliased text remains open. I would tend to agree with David's assessment of the situation: the question of the *utility* of grayscale text remains open. Depending on the task at hand, 'utility' might mean discriminability, legibility, readability, aesthetics, or some combination of these qualities. Several research projects have started *preliminary* work into investigating the issues involved [Bender 87, Farrell 88, Gould 84, Gould87a, Gould 87b, Naiman 88]. However, it is premature to draw generally applicable conclusions from any of the published research (at least, that which I have seen). Furthermore, in having spoken with at least one author of each of the papers I reference (and many other researchers in the field), I believe they all agree that we still have much to do before anything close to an 'all-encompassing' grayscale font production system is available. Other than pragmatic-type problems (e.g., how fast can the fonts be produced), some of the issues which need addressing include: -- algorithmic processes for generating grayscale fonts -- appropriate filters -- tradeoffs between number of grayscale levels and resolution -- the visual system's response to grayscale edges -- the relationship between flicker and grayscale -- fatigue of the visual system -- sub-pixel positioning -- 'difference' metrics for multiple versions of a character -- display device modeling >John Peterson > Not really, some studies have been done. I have in front of me a paper > titled "CRT Typeface Design and Evaluation" that was prepared by some people > at MIT and IBM. In their study they found that people can read a display > with anti-aliased fonts -faster- than the equivalent hardcopy text. This > compares quite well to traditional CRT text, which was found consistantly > slower than hardcopy. >From my experience, I find it hard to believe that one can today compare a screen font (regardless of whether or not there is grayscale) with an *equivalent* hardcopy sample. Aside from the fact that the illumination levels of the two media are quite different (one being steady and reflective, the other refreshed and emissive), the point spread functions will likely be quite different. Hence, the character shapes will be distorted by the two media in different ways. While we can try to minimize these differences, until we have established metrics by which to measure the 'differences' between two versions of the same character (in terms of the performance of the human visual system in some task domain), we will not even know what 'nominally equivalent' means. On the bright side, there have been certain controlled, focused -- and limited -- experiments which have demonstrated that, under suitable conditions and for given tasks, subjects can use a 'particular' grayscale font to better advantage than a 'particular' hardcopy font. Since John brought up the [Bender 87] paper, let me illustrate my remarks (both the limitations of completed research and the need for much more) with some quotes from, and remarks on, the article [note that the authors do not make exactly the same claim John describes]: -- "To *begin* to understand this question" ['*' are mine] -- "... we have designed a new [sic] anti-aliased typeface which can be viewed on an analog color display." How are things affected when monochromatic grayscale monitors are used? How is "color" accounted for? -- "[video display] technology presents advantages and limitations never considered in the design of typefaces for printed communication." This implies -- correctly -- that there is much we do not yet understand about "digital typography", let alone grayscale fonts. -- "Most CRT typefaces attempt to imitate printed typefaces, and their design is not optimized for CRT's. It was our intention to design this new typeface on the media for which it was ultimately intended." Three possibilities exist: the grayscale font is an implementation of the hard-copy font, the hard-copy font is an implementation of the grayscale font, the grayscale font is similar to, but not the same as, the hard-copy font. By their own admission, the grayscale font used in the experiment was derived from a hard-copy font, but was re-designed for the video terminal. Hence, the media is not the only thing that was different between the font samples. -- "In our experiment, we had a graphic designer hand-tune the algorithmically generated grayscale characters." How would the grayscale font have fared without hand-tuning? Is hand-tuning feasible for large-scale font production? -- "It is important to find a common ground between acuity and positionability. ... His experienced eye was used to find a balance between the acuity and shape of each character." How can we incorporate the designer's aesthetic sensibility into an automated process? In what ways is the 'solution' task-dependent? -- "In addition, he designed a typeface which was well-suited for CRT display; the smallest elements of the characters ... were on the scale of a pixel." How well will more traditional typeface designs transfer to the grayscale media? Will this prove more successful than black and white versions in capturing subtle design details? -- "It is our guess that the application [of] typographic skills to our character design, as opposed to simply the application of filters, however well-tuned, is the factor which has significantly improved the readability of our anti-aliased characters over previously reported results. [Gould 1984]" Note that the authors themselves are questioning exactly what role the grayscale media played in 'improving' the quality of the CRT font. Furthermore, the "control for this study was hardcopy printed on the IBM 5218 Printwheel Printer with a Prestige-Elite Printwheel II". Ideally, one would like hand-tuned and untuned versions of black & white as well as grayscale fonts, in order to separately evaluate the issues of grayscale, typographic skills, and media. Furthermore, since their grayscale font was Century Schoolbook-like [private communication], how justified are the results? I do not contest that the particular grayscale, hand-tuned, CS-like, CRT-displayed font out-performed the hard-copy, Prestige-Elite one; but what conclusions are fair to draw from this fact? In fact, they make essentially the same (implied) observation: "Future work will include a direct comparison of algorithmically generated fonts with hand-tuned fonts, as well as a comparison between the same typeface, hand-edited bi-level and grayscale." -- "The data suggests that proofreading with the new anti-aliased [sic] typeface on an analog color display is faster than from a hardcopy". For the particular sample fonts and task used! Would it have been faster than high-quality typeset hard-copy fonts? -- "Only six out of eighteen [preferred] the printed copy. ... Although not significant, this result does suggest a trend that deserves further investigation." Indeed it does! I hope no one construes this posting as an attack on the [Bender 87] work. I am merely trying to illustrate some of the complexities involved in using grayscale on a widespread basis. I'm all for it; I just don't know how to do it consistently *well* yet (nor, do I believe, does anyone else). Avi Naiman Dynamic Graphics Project Department of Computer Science University of Toronto avi@dgp.toronto.edu Bender 87 Bender, W., R. A. Crespo, P. J. Kennedy, and R. Oakley, ``CRT Typeface Design and Evaluation,'' Proceedings of the Human Factors Society, 31st Annual Meeting, 1987, pp. 1311-1314. Farrell 88Farrell, J. E. and A. E. Fitzhugh ``Image Quality of Digital Characters,'' Supplement to Investiga- tive Opthalmology and Visual Science, 1988, In Press. Gould 84 Gould, J. D. and N. Grischkowsky, ``Doing the Same Work with Hard Copy and with Cathode-Ray Tube (CRT) Computer Terminals,'' Human Factors, Volume 26, Number 3, June 1984, pp. 323-337. Gould 87a Gould, J. D. et al., ``Why Reading was Slower from CRT Displays than from Paper,'' Proceedings of CHI+GI 1987, April 1987, pp. 7-11. Gould 87b Gould, J. D. et al., ``Reading is Slower from CRT Displays than from Paper: Attempts to Isolate a Single-Variable Explanation,'' Human Factors, Volume 29, Number 3, June 1987, pp. 269-299. Naiman 88 Naiman, A. and J. Farrell, ``Modeling the Display and Perception of Grayscale Characters,'' SID 88 Digest, Volume 19, May 1988, pp. 424-427. -- Avi Naiman avi@dgp.toronto.edu