Mystery FontLab Type 1 Autohinting Dialog Box

Richard Fink's picture

Mystified by the third box in the FontLab Hinting Settings section.

There's only a single sentence about it that I could find in the FontLab manual.
I asked some folks at Adobe about this and, since they use tools developed in-house, they had no clue - not even an educated guess about what these settings do.

In FontLab's Hinting Settings:

- Standard Stems (T1 hinting)
- Additional hinting parameters

This next one is the mystery:

 - T1 Autohinting

(Gif image attached to this post and posted here, too: Type 1 Settings - FontLab

It has one row for 'Horizontal' and another row for 'Vertical', with fields for:

'MinWidth', 'MaxWidth', 'MinLength', and 'Aspect Ratio'

Twardoch, anybody? What do these settings do?

I'm no stranger to trial-and-error experimentation, but a clue would be nice.
Besides, it's odd that there's nothing specific about it in the manual.

Thanks.

Rich

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mekka's picture

Isn't that pretty self-explanatory?
What is it that you don't understand about 'MinWidth', 'MaxWidth', 'MinLength' etc.?

Té Rowan's picture

I think there are quite a few references, books and tutorials on T1 hinting out on the Net.

Richard Fink's picture

@mekka
"Isn't that pretty self-explanatory?
What is it that you don't understand about 'MinWidth', 'MaxWidth', 'MinLength' etc.?"

Well, obviously you've explained it to yourself since it's pretty self-explanatory.
Maybe I'm stupid. Would you mind sharing it's meaning with me?

It's not obvious to the head of the Adobe type group, I can't know for sure but I think he'd be amused by the notion that you're a step ahead of him. Ted Harrison of FontLab doesn't know either. The manuals for both the current and previous version of FontLab say little more than it exists. Not what it does or what the values control.

@té
There are no books on T1 hinting. If you know of any, I'm all ears. What tutorials and references there are don't give any clue as to what these values control.

agisaak's picture

Since Type 1 hinting is applied to stems, I'd assume these options control how FontLab identifies stems to be hinted. Features which are smaller than minWidth, larger than MaxWidth, or shorter than MinLength won't be treated as stems and thus will not be hinted. Features which fall within these parameters but which are outside of the stated aspect ratio presumably also won't be hinted.

André

Té Rowan's picture

Hm. Was sure my memory had not been inventing things. Grmbl.

John Hudson's picture

I'm not sure how 'Aspect Ratio' applies, so generally leave that at default. The others are fairly self-explanatory. Each is a setting that determines what the FL autohinter will treat as a stem for hinting purposes.

MinWidth and MaxWidth respectively determine the narrowest and widest stems that will be hinted. Note that these are in absolute units per em, so if your font has a UPM of 2048, for instance, you'll likely want different values in here than if the font has a UPM of 1000.

MinLength is the length of *straight* stem that will be hinted, so might be set to ignore very short segments. Note that the autohinter seems not apply this to curves, which are hinted or not based only on MinWidth and MaxWidth settings.

In general, you want to set these values on a per font basis -- which is why the settings are part of Font Info and not an FLS options setting -- because they should reflect typical stem values in the font. You do not want to set the MaxWidth too large, because otherwise you will generate a lot of overlapping hints as FontLab. Obviously you want your MinWidth to be small enough to capture the thinnest stems that you want to be hinted, so in the case of a Light or UltraLight font this value will need to be small.

Richard Fink's picture

@jh

Thank you, sir.
I'm a little pressed for time right now but will come back in a couple of hours to digest. I might have a question or two, if you'd be so kind as to provide clarification.

"Aspect Ratio" seems, so far, to be a total mystery to everybody I've asked.

Adam Twardoch in the house? Yuri? Anybody.

rich

Richard Fink's picture

@jh

"In general, you want to set these values on a per font basis -- which is why the settings are part of Font Info and not an FLS options setting -- because they should reflect typical stem values in the font"

I've found that these settings are "sticky". Once changed, they stay changed for the next font opened and thereafter, too. Until changed.

Going to experiment a bit. Thanks for the Blues Clues.

rich

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