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Re: [Freetype] de-blurring / sharpening / hardening

From: Peter Montgomery
Subject: Re: [Freetype] de-blurring / sharpening / hardening
Date: Wed, 12 Feb 2003 15:28:52 -0800


> Noticing that simple scaled bitmap glyphs are very "sharp" but
> unattractive and AASB glyphs are blurry and attractive I tried
> modifying the AASB glyphs by "pushing" them toward the simple
> scaled scaled bitmaps. I did this by applying a non-linear
> weighting of the pixels after the AA scaling. This does not
> make the glyphs perfectly sharp but it does visually reduce
> the blurryness.

Yeah, basically all you're doing is increasing the contrast of the
images.  A simple lookup table can be used to do this with the result
being a reduced number of intermediate gray steps and an apparent
increase in sharpness.  An alternate (slower) approach is to render the
images larger than needed and then scale down using a truncated sinc
filter.  Since the sinc function has negative lobes, it provides some
sharpening as a by product of the resampling process.  However, the
lookup table approach is far faster and you can go so far as to create a
lookup that has half the entries as 255 and half as 0.  The result will
turn antialiased images into completely aliased images like a "typical"
desktop style font rendering.


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