Re: [ft-devel] Tweak CJK Blue zone parameters

[suzuki toshiya]

I attached 3 pictures comparing 4 cases for Japanese hi quality commercial
PostScript fonts (Ryumin-Light, GothicBBB-Medium and Shuei-Min. Ryumin-Light
and GothicBBB-Medium would be the most referential font in Japanese market
because they are bundled to most PostScript printers).

I thought using hi quality font can exclude the issue that should be improved
by the further insertion of the control points.

The results in the picture from top to bottom are:
anti-alias without hinting,
anti-alias with autohinter without CJK bluezones,
anti-alias with autohinter including CJK bluezones,
anti-alias with autohinter including CJK bluezones with proposed tweak for 16pt 
or smaller

The autohinter improves the contrast of the strokes.
In my understanding, CJK bluezone is designed to improve the strokes
around the square boundaries, but it improves the contrast of the
internal strokes too. For example, please find "口" in "吉" or "合"
glyph in Ryumin-Light picture.

However, if you see the difference of "官", the autohinter is not
always improving. The result in GothicBBB-Medium (Sans Serif style)
is improved, but Ryumin-Light and Shuei-Min are not improved.

The improvement by the proposed tweak for 16pt or smaller seems to be subtle.

Werner LEMBERG wrote:
>> Now that the CJK blue zone code are in the freetype repository,
>> further tweak on the parameters can be performed.
> 
> Could you provide test images of various CJK fonts, demonstrating the
> effectivity of your improvements?  Ideally, there is a large set of
> such images which can be then compared mechanically to immediately see
> the differences.
> 
> 
>     Werner
> 
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