private IEnumerable <Point> GetSubpixelPoints(Point p)
 => new Rectangle(p.X * WidthZoomFactor, p.Y * HeightZoomFactor, WidthZoomFactor, HeightZoomFactor).Area;
 private IEnumerable <Color> GetPixels(Bitmap bmp, Point p)
 => GetSubpixelPoints(p).Select(p => bmp.GetPixel(p.X, p.Y));