vec4 sepia(vec4 color)
{
    float r = color.r;
    float g = color.g;
    float b = color.b;

    color.r = r*0.393 + g*0.769 + b*0.189;
	color.g = r*0.349 + g*0.686 + b*0.168;
	color.b = r*0.272 + g*0.534 + b*0.131;
    return color;
}