Hinting: Current: £ and € ambiguity at 13/15 ppem (difficult to read at small sizes)

[Mackenzie Morgan]

I'm using Kubuntu Netbook, which defaults to size 7 & 8 fonts. At these sizes, the £ and € symbols become a bit difficult on the eyes. I'm attaching a screenshot comparing the Ubuntu font and Liberation Sans at sizes 7, 8, and 12 so the difference can be seen.

Mainly, I think the bottom line of £ needs to extend further to the left like it does at size 12 (at sizes 7 & 8 it almost looks like a C with a graphical artifact making it slightly crooked) and that the €'s bars should be a bit closer together since at sizes 7 & 8 it turns into a muddle of horizontal lines with the top edge, two bars, and bottom edge all being equidistant.

The screen is running at its native 1366x768 and is 11.6" (256mm x 144mm) making a DPI of 135. And yes, KDE obeys the X DPI. The DPI is being forced with `xrandr --dpi 135` in /etc/kde4/kdm/Xsetup since the autodetection was wrong

[Paul Sladen (sladen)]

135 dpi at 7/8 pt makes this 13/15 ppem, this appears to be rendered with hinting enabled, so I can see the potential for tweaking it. Perhaps in the hinting for the node at the bottom-left of the £ would do with pushing out a bit, so that the rasterised shape has less of a curved/'C' appearance at smaller sizes; eg. more akin to the Hebrew bet ('ב') in reflection and a more definite corner.

maco: to confirm, please can you retake the screenshot with the magic '' character pasted in after each of the pound signs. This will confirm the hinting and ppems in use.

[Mackenzie Morgan (maco.m)]

Adding in a debugging glyph at sladen's request

[Paul Sladen (sladen)]

Confirmed per second screenshot.

[Shiraaz Gabru (shiraaz)]

Thanks for the feedback, looking at the screen shots attached, the £ and € symbols don't seem ambiguous to me at the point sizes specified. The two middle horizontals are visible even at the 7 points.

[Mackenzie Morgan (maco.m)]

When they're sitting an inch apart, you can tell them apart, but the first time
I typed £ I was confused because it looked more like a crossed-C than a
crossed-fancy-L with the lack of little...thingy...sticking out the left side.

I imagine the DPI with which you view the screenshots would make a difference
to what you see too though. As in the original report, my screen is 135 DPI,
which means my pixels are about 3/4 the size of "normal." Maybe try scaling it
down to 75% in the GIMP and look at it?

[David Marshall (dave-daltonmaag)]

The DPI setting isn't relevant here as we're specifying the
"problematic" sizes in ppem. I don't believe the shapes are ambiguous in
themselves or with each other, even at such small sizes, and the choice
of form for the £ is standard for a sans-serif typeface. You wouldn't
expect to see a loop on a sans-serif £ design.

Dave

[Paul Sladen (sladen)]

David: I what is happening here is that the feature that makes the £ unambiguous is the concave knee at the bottom left, but the current hinting loses this at 13/15 ppem by snapping to the vertical, rather snapping in the opposite direction (to be level with the left-hand extent of the cut-line). See the attached PDF for what is happening and the likely solution ensuring that the knee always remains concave.

[Paul Sladen (sladen)]

...and the PDF version of that.

[David Marshall (dave-daltonmaag)]

I'm afraid that proposed solution - which exaggerates the feature - will
result in a very unpleasant shape. Unambiguous, but glaringly ugly. I
would contend that the current solution is completely unambiguous, however.

Dave

[Mackenzie Morgan (maco.m)]

Here's a screenshot of the £ character at 13ppem in every sans-serif font on
my system. All but Ubuntu have that concavity. Some even have a ~ shape to
the bottom line. There are only two I'd call ugly (Deja Vu & URW Gothic)

[David Marshall (dave-daltonmaag)]

Ah, apologies - that's a different issue to the one I'm referring to -
the horizontal stem at the bottom should extend to the left of the
vertical stem in this case, because we can't preserve the slight
curvature without overly-distorting the character.

So yes, I would amend the current form, but by clarifying the bottom
stem, not by distorting the vertical stem.

Dave

[Paul Sladen (sladen)]

Dave: I don't really mind how it's done, as long as in the hinted forms, the bottom-lefthand node is always rendered >= 1-pixel past the left of the main vertical stem! :)

It's "only" 1-pixel, but that pixel is critical in preserving the legibility of the /apparent/ shape.

[Paul Sladen (sladen)]

Screenshot of PDF rasterised at approximate sizes under discussion. Hopefully showing how the suggested hinting adjustment should improve the legibility whilst increasing the /perceived/ similarity to the true outline form with its slight back-kick in the bottom-left.

[David Marshall (dave-daltonmaag)]

Yes, I'm in complete agreement that the bottom horizontal stroke needs
to clearly extend beyond the vertical. I was arguing at cross-purposes
earlier.

Dave