I came across this magnificent specimen recently—Sharp Type’s Carta Nueva by My-Lan Thuong, 4096 units to the em—and wondered which other typefaces have ventured into such expansive territory.
What is the main disadvantage of high UPM (let's say above 2000)? I guess font size, but maybe some other things like compatibility with some text processing apps, problems on the web, etc.?
If you have a large upm setting and very wide glyphs, it may cause the coordinates to break some systems.
E.g. if a glyph is 3 em wide, and has a point at x = 12000, and the rasterizer uses an oversampling factor of 5 in x-direction, the coordinate will land at 60000. If the rasterizer should happen to use signed short integer values for calculations, only numbers between -32,768 and 32,767 can be handled. Of course, rasterizers usually don't use the unscaled coordinates, but will scale them to 1/64th pixel first.
But I think I remember that e.g. Windows could not display a very wide glyph with ClearType. That may be a thing of the past now.
Comments
an em: the unit.
the Em: the number of units composing the height.
(Although usage certainly varies.)
I spose I should have written “4096 units to the em-square”?
But anyway—other “big em-square” fonts?
is mathematically synonymous with
u = m/4096
and
4096 * u = m
E.g. if a glyph is 3 em wide, and has a point at x = 12000, and the rasterizer uses an oversampling factor of 5 in x-direction, the coordinate will land at 60000. If the rasterizer should happen to use signed short integer values for calculations, only numbers between -32,768 and 32,767 can be handled. Of course, rasterizers usually don't use the unscaled coordinates, but will scale them to 1/64th pixel first.
But I think I remember that e.g. Windows could not display a very wide glyph with ClearType. That may be a thing of the past now.