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Re: [ft-devel] [Patch] CJK autofit/autohint blue zones

From: JustFillBug
Subject: Re: [ft-devel] [Patch] CJK autofit/autohint blue zones
Date: Fri, 14 Jan 2011 12:10:36 +0000 (UTC)
User-agent: slrn/pre1.0.0-18 (Linux)

On 2011-01-13, Miles Bader <address@hidden> wrote:
> The "with blue" and "no blue" renderings are surely different, in terms
> of vertical alignment at the bottom, but it's not clear to me which is
> actually _best_... the "no blue" rendering looks more even though.
> What are the rules about vertical alignment with CJK fonts?  [Especially
> at low resolutions, where many characters end up having wide flat
> bottoms even if they're not flat at high resolutions.]
> In particular, these two characters: "置者" look a bit unbalanced in the
> "with blue" rendering, but look nicer to me in the "no blue" rendering
> because at least their flat bottoms are aligned.

Two things.

1. There are always some chars that have higher bottom lines either by
   design or by mistake. Chars like 日, 士 might be designed to have a
   higher bottom in certain fonts. Which cannot be corrected by auto

2. Parameters used by the auto hinter are choosen by experience. A set
   of parameters perfect for one font at certain scaling size might not
   be very good for another font or at another scaling size.

   The patch inherited blue zone threshold parameters of latin script.
   Which is 1/40 of EM for the zone width, and max out at 1/2 pixel.

   Since ideographs are more sensitive to bottom line alignment at
   smaller font size than latin glyphs, we can relax those parameters
   some more.

   If I choose 1/32 of EM, max out at 3/4 pixel, I will have wider
   alignment range up to 16 ~ 18 font size for this particular font.

If the blue zone hinting for CJK is accepted as useful, then adjusting
the parameters is something that have to be done by people with a lot of
fonts. I don't have much fonts myself.

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