private void DrawBrightnessPointer(Point pt)
{
const int height = 10;
const int width = 7;
var points = new Point[3];
points[0] = pt;
points[1] = new Point(pt.X + width, pt.Y + height / 2);
points[2] = new Point(pt.X + width, pt.Y - height / 2);
this._graphics.FillPolygon(Brushes.Black, points);
}