BlueScale default value?

I’ve set up autohinting on my latest project and I’m happy with the results.

I was going to add a parameter for BlueScale to suppress overshoots at a reasonable size but it occurred to me that the autohinter may add a default value automatically. Or does it just keep suppressing until a full pixel is available to show the overshoot in proportion?

According to the original Type 1 spec,
“The default value of BlueScale is .039625” (p.40).

My understanding is that by default, Glyphs does not write any BlueScale value into the font (which is possible), which triggers this default.

My personal opinion is that this is too low; I usually end up with something between 0.6 and 0.9.

If in doubt, or during the early stages of the design process, it does not hurt to use a very high value, which practically leads to the behaviour you described, “just keep suppressing until a full pixel is available to show the overshoot in proportion”.

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Thanks Tim, that’s very helpful.


I’m still having a few issues with the blueScale.

I just read in the Glyphs manual that the blueScale default it uses is 0.037, so should stop suppression at 40px at 72ppi (20pt retina)

However, I’m seeing this stop much earlier in my font, at 14pt (retina):

Font 1000 UPM
Overshoot of 12 units
BlueScale Default
BlueFuzz = 0
14pts (InDesign, Retina @100%) overshoots are unsuppressed

Then, if I add a blueScale value of 0.050, I’m seeing it stop at 17pt (retina) instead of about 26pt.

Any thoughts? Have I got my scale wrong somewhere?

Also, I’ve set my blueFuzz to 0 but is that the default anyway?

First of all, when talking about BlueScale, it’s much easier to completely forget about all things pt and dpi, and only consider ppem (or px, which is identical).

My guess is that the “100%” zoom in InDesign has no meaning. You could take a screen shot, measure the cap height (in px) and compare it to the cap height (in units). That gives you an idea of the ppem you are looking at. Or, simply use Photoshop directly to test your font, create a text layer, and set the type size in px.

Ideally, to test and set BlueScale – and I consider this a very important decision during the design and production of a font –, you should view your font in a browser on Windows. Alternatively, you can work with waterfalls and simply adjust the BlueScale up or down until it looks right to you (this is possible without even knowing the ppem you are looking at). Working on a Retina screen, this may be tricky, though. So, maybe Photoshop is the better workflow if you don’t have access to Windows.

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Thanks again Tim, Happy to judge it visually. The eye rules after all.

It’s just a bit strange that my 15pt = 30px (matching @mekkablue 's blueScale chart), yet the bS value is so far out.