Re: [ft] Enabling Subpixel Rendering On freetype-2.7.1

[Wojciech Mamrak]

> This is not correct.  Normal hinting is intended for xppem = yppem.
> Subpixel hinting, however, is a special mode to adjust hints in
> TrueType fonts so that you get good rendering results for xppem =
> 3*yppem, i.e., the resolution along the x axis is increased by a
> factor of three.

> Regarding the `explosion', please read the beginning of Greg's
> whitepaper on ClearType.

>  https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx

> Note that the new ClearType mode from Nikolaus has superseded the
> Infinality mode (which was very slow and no longer actively
> maintained).

Just to clarify, when subpixel hinting is on, glyphs are hinted to
full pixels in vertical direction, and horizontal hints are ignored
[1]

[1]  https://www.freetype.org/freetype2/docs/subpixel-hinting.html

2017-03-27 7:49 GMT+02:00 Werner LEMBERG <address@hidden>:
>
>>> possible, be aware that some old fonts might `explode' in this
>>> mode.
>>
>> Why would the old fonts "explode"? I thought the "subpixel hinting"
>> was contributed from Infinality and it works best with modern fonts
>> without good hinting.
>
> This is not correct.  Normal hinting is intended for xppem = yppem.
> Subpixel hinting, however, is a special mode to adjust hints in
> TrueType fonts so that you get good rendering results for xppem =
> 3*yppem, i.e., the resolution along the x axis is increased by a
> factor of three.
>
> Regarding the `explosion', please read the beginning of Greg's
> whitepaper on ClearType.
>
>   https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx
>
> Note that the new ClearType mode from Nikolaus has superseded the
> Infinality mode (which was very slow and no longer actively
> maintained).
>
>> Is it true that, without "subpixel hinting" FreeType2 will just hint
>> fonts to "full pixels" which is exactly the scenario the old fonts
>> was developed?
>
> Correct.
>
>> I think the fonts would look sharper that way.
>
> Good B/W hinting is *very* expensive to add to fonts since you have to
> take care of the exact pixelation; there are just a handful of
> well-paid experts who are doing that, and only a handful of fonts that
> have such hints at all – mainly the screen fonts that come with
> Windows XP and older.  On the other hand, grayscale hinting can be
> done quite well automatically (ttfautohint, VTT).
>
> To get `sharper' rendering you have to increase the sampling frequency
> along the x axis; there are various possibilities how to do that.
> FreeType's solution is, as mentioned above, to increase the horizontal
> resolution, taking care of special situations that would yield to
> wrong hinting.  Microsoft's solution is super-sampling (which is the
> superior approach IMHO), as explained in the whitepaper.
>
>
>    Werner
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