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Re: [ft-devel] gamma correction demo images

From: Alexei Podtelezhnikov
Subject: Re: [ft-devel] gamma correction demo images
Date: Mon, 23 Nov 2015 09:48:18 -0500

On Sun, Nov 22, 2015 at 7:49 AM, Nikolaus Waxweiler <address@hidden> wrote:
> And, uh, is the light filter color balanced?

Yes, it is almost perfectly color balanced. This means that color
contributions are equal, i.e., b + a  = c in filter [a b c b a]. This
is what is imposed when people specify filters as  [a-c, a+c, 2a, a+c,
a-c]. The light filter { 0x00, 0x55, 0x56, 0x55, 0x00 } is indeed
almost perfectly color balanced and normalized, which is what we need.

Freetype's default filter { 0x10, 0x40, 0x70, 0x40, 0x10 } is neither
balanced nor normalized. The comment speaks about "cheap gamma
correction" through inflating the resulting values and clipping them
above 1. This is very wrong! You never should apply any gamma to alpha
channel to begin with. For the white-on-black text the effect would be
opposite of gamma correction if anything.

There you go, the lack of proper gamma correction results in a bad
filter being chosen as default.


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