13 Aug 2004 raph   » (Master)

Musings on fonts

I've been kinda immersed in fonts for the past week or so, and have some things to share with you font nuts out there.

First, I've picked a font revival to work on: ATF Century Catalogue. I think this may be one of the most underappreciated fonts out there. It's definitely a representative of Beatrice Warde's Crystal Goblet theory of font design, as opposed to all the ego-driven stuff work churned out now.

In particular, I believe an adaptation of Century Catalogue is an excellent candidate for a font to supplant Computer Modern as a font for setting math. In addition to aesthetic beauty, an important consideration is continuity with existing traditions of math typography. A great many math texts in the last century have been set in Monotype Roman No. 8, of which Knuth's Computer Modern fonts are a reasonably accurate digital revival. But this is far from the only font well represented in the literature, nor, arguably, the best.

The model that Knuth acknowledges as the most aesthetically pleasing is Volumes 23 and 24 of the Transactions of the AMS (see p. 20 of his book, Digital Typography). The sample he shows appears to be set in a variant of Monotype Old Style (not exactly No. 2, as the tail of the 'c' in the latter are curved up more). Even so, he doesn't like some aspects, for example the angularity of the italic 'x'.

I agree that the shape of the italic 'x' is important - indeed, to me, it strongly connotes variableness, in much the same way that a copperplate gothic connotes the style of a banker or lawyer, or Old English Gothic connotes an old-style newspaper banner.

So, after looking at dozens of fonts, I've concluded that Century Catalogue is the one. The roman resembles the Monotype Old Style fairly strongly, but is in my opinion better drawn (by master typographer Morris Benton Fuller). In addition, its italic (which is more closely based on ATF's Baskerville Italic than a member of the Century family, but is nonetheless stylistically quite coherent with the Roman) is much closer to what people now expect from math fonts.

Gain

Perhaps the biggest complaint about Computer Modern is that it's too light. Both the weight of vertical stems, and the relative weight of serifs and hairlines compared to the vertical stems are lighter than mainstream text fonts.

When I got my copy of Knuth's Digital Typography, I was struck by how much better it looked than most of the TeX output I'm used to seeing, especially from laser printers. I now believe I know the secret: press gain, probably in this case introduced deliberately to make the body text look good. You can see the effect pretty clearly in my 2400dpi scans.

What is the best primitive for curve design?

Most 2D curve design (including fonts) done today uses cubic Bezier splines. Almost all of the remainder is quadratic Beziers. There are other choices, and I wonder if some might be better.

In particular, I find it tricky to make smooth curves when there are a lot of control points. I'm sure it gets easier with practice, but I'm not sure people should have to adapt to the underlying polynomial nature of the spline, when perhaps smoother, more natural primitives exist.

For example, Ikarus used Hermite splines, in which all the control points lie on the curve. In Beziers, you have to position the off-curve control points so that they "magically" adjust the curve how you want it.

From what I can see, the main reason inexpertly drawn Beziers look unsmooth is large variations in curvature, both discontinuities at the knots and in greater deviation in curves than needed to smoothly connect the endpoints. I'm thinking of building a tool that graphs curvature along the path of an outline. I have little doubt that this tool's output would reveal much less variation and discontinuity in splines drawn by experts than by newbies.

So, to me, the most promising approach is to use a primitive that has smoothness of curvature built-in, so that by default it's easier to draw smooth curves than unsmooth. Of course, it should still be possible to do the latter, but I have no problem with making it require more control points than an equivalent unsmooth Bezier curve.

The most promising primitive I've seen so far is the "circle spline" of Carlo Sequin and students [SIGGRAPH PowerPoint presentation]. Near the end of that presentation, he raises the possibility of using a Cornu Spiral, which is mathematically constructed so that curvature is continuous at endpoints, and linearly interpolated in between.

For those more interested in this issue, John Hobby's paper "Smooth, Easy to Compute Interpolating Splines" is a must-read. My gut feeling is that his work is good, but that replacing his choice of cubic Bezier as a primitive with a circle spline or Cornu Spiral may give better results. He found that making curvature continuous can yield instable results, so he uses a linear approximation which guarantees stability. I wouldn't be surprised if this instability would go away with a better primitive.

Ripoffs

The Wikipedia is fun (and I've been contributing a bit to it), but one of the things that really irritates me is how ripoff sites usually manage to get higher Google rankings than the real thing. Most people don't know better, and often link to the ripoff pages, further strengthening their rank.

It's not just the wikipedia, of course, even though that's a notable and recent case. If you go searching for free fonts, you don't come across many sites of people who've put time and effort into creating, collecting, and critiquing the fonts, but you sure do find the ones that aggregate thousands of fonts (most of which are ripoffs of proprietary versions themselves), then presumably make some money off ads and whatnot.

I'll be releasing the math fonts under some form of free license so that they can be included in Ghilbert, of course, but it would be nice if there were some way to discourage them from being ripped off. If I continue to make fonts, I'm tempted not to release them freely, partly because of the ripoffs, and partly because free fonts are seen as junky.

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