Re: [Devel] Freetype2 & gamma correction

[Keith Packard]

Around 23 o'clock on Mar 28, Matthijs Melchior wrote:

> Despite all the positive noise I saw, I did not like the way the text
> looked, it was rather uneven...

This situation is not caused by gamma, but a separate effect caused by the
the gaussian nature of CRT pixels.  To adjust for this effect, you want to
artificially increase the apparent pixel coverage for areas partially
covered by the glyph.  This appears similar to "gamma" correctly, but in 
reality is unrelated.

> The ideal situation would be that freetype automatically ajusts
> to the gamma setting of the output device it is using.

This won't work because FreeType doesn't know what colors are involved and 
the values needed are different when rendering light text on a dark 
background compared to rendering dark text on a light background.

The right place to adjust the intensity mapping is down in the rendering 
code.

So, we really need two fixes -- one fix to adjust the partial coverage 
values to accomodate the output device pixel characteristics, and a gamma 
correction to adjust for output device luminosity behaviour.

The happy coincidence is that for dark text on a light background, these 
two effects cancel each other out when you leave the monitor uncorrected.

-keith