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Re: [ft-devel] gamma correction and FreeType
From: |
Werner LEMBERG |
Subject: |
Re: [ft-devel] gamma correction and FreeType |
Date: |
Fri, 01 Nov 2013 06:31:07 +0100 (CET) |
Dave,
thanks a lot for your good demonstration images!
> I believe column 3 is what we want to achieve.
Yes, indeed! By the way, here is another page which goes into great
detail on gamma correction and TrueType font rendering:
http://www.beatstamm.com/typography/RTRCh5.htm#Sec3
It might be interesting to see your tests applied to common TrueType
fonts also. Beat Stamm writes about GDI ClearType:
In Windows, text rendered in full-pixel anti-aliasing is displayed
with a gamma correction done in software and using a gamma value of
about 2.3 – to determine this γ value, I displayed a gray ramp in
Word, inspected the RGB value of middle gray as rendered (189),
solved L = V(1/γ) (the formula for γ correction, as opposed to γ
response) for γ, and substituted the normalized inspected gray value
(189/255) for L while setting V to 0.5 (half the normalized voltage
should yield middle gray). Thus γ = log(V)/log(L) =
log(0.5)/log(189/255) ≅ 2.314. This gamma correction appears to be
in addition to what my premium graphics chip wants to do. If I
“under-correct” gamma on my graphics chip, all my photos look too
dark in their midtones, but text rendered in full-pixel
anti-aliasing looks more natural. If I “correct” gamma for my
photos, text rendered in full-pixel anti-aliasing looks “washed
out.” Windows (GDI) does not have any provisions to adjust or
defeat the software gamma correction of full-pixel anti-aliasing
(“standard font smoothing”).
So it seems that similar problems are affecting even major
platforms...
Werner
- Re: [ft-devel] gamma correction and FreeType,
Werner LEMBERG <=