From: "Filsinger, Andreas (Softwareentwicklung)" <andreas@filsinger.de>
To: <efg2@efg2.com>
Subject: Suggestion for additional "Color Project"
Date: Monday, October 08, 2001 5:43

Earl,

i had to place text on a coloured backgound. I knew the color of the background, now i had to calculate automatically the Font-Color viewed best on the specific background-color.

My first try was "textcolor := BackgroundColor xor $FFFFFF". That results in well visible (but funny) Font-Colors, but fails if the background is grey.

Next i set Font-Color to "white" on dark backgounds, and "black" on bright ones. But what is Brigthness? (R + G + B) / 3 seems to be a good value. It fails because the human eye does not see all the colours in the same density.

Next i read something about "Luminanz" and created my final code:

function VisibleContrast(BackGroundColor : TColor):TColor;
const
 cHalfBrightness = ((0.3 * 255.0) + (0.59 * 255.0) + (0.11 * 255.0)) / 2.0;
var
 Brightness : double;
begin
 with TRGBQuad(BackGroundColor) do
  BrightNess := (0.3 * rgbRed) + (0.59 * rgbGreen) + (0.11 * rgbBlue);
 if (Brightness>cHalfBrightNess) then
  result := clblack
 else
  result := clwhite;
end;


in the picture you can see more than my (perfect) english ever will imagine.

Andreas