[marcoszorrilla]

Prueba esto a ver si lo solucionas:

Código Delphi [-]
#45: How can I convert color value into gray-scaled color value?

If you want to convert a colored image into same gray scaled, then you must convert the color of the each pixel by the next schema:

function RgbToGray(Source: TColor) : TColor;
var Target: Byte;
begin
  Target := Round((0.30 * GetRValue(Source)) +
        (0.59 * GetGValue(Source)) +
        (0.11 * GetBValue(Source)));
  Result := RGB(Target, Target, Target);
end;

Un Saludo.