Re: [ft-devel] gamma correction and FreeType

[Werner LEMBERG]

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