sepia function
Implementation
RGBA sepia(RGBA color, num adj) {
int r = color.red, g = color.green, b = color.blue;
return new RGBA(
red: clampPixel(
((r * (1 - (0.607 * adj))) + (g * .769 * adj) + (b * .189 * adj))
.round()),
green: clampPixel(
((r * .349 * adj) + (g * (1 - (0.314 * adj))) + (b * .168 * adj))
.round()),
blue: clampPixel(
((r * .272 * adj) + (g * .534 * adj) + (b * (1 - (0.869 * adj))))
.round()),
alpha: color.alpha);
}