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

[Just Fill Bugs]

On 05/12/2011 01:02 AM, suzuki toshiya wrote:
> 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).

Thanks for generating this sample for comparison.

> 
> 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.

I did not see anything that indicate the blue zone would effect middle
stems in the code. You might want to trace af_cjk_hint_edges() with the
given character to see why the alignment was skipped at the middle
without blue zone.

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

Here's the characters I can see the 16pt tweak made differences.
GothicBBB: 旦, 吉
Ryumin-Light: 品
ShueiMin:   占

Actually, these characters are the main targets of the patch. These
chars have less strokes so they are normally designed to be shorter than
the normal characters, i.e. their bottom lines are outside of a smaller
blue zone.

The patch try to catch these chars at the small font size.