/// <summary>
/// Gets the opaque pixels in a bitmap as a Region object.
/// 获取一个位图中的不透明像素并作为一个 Region 对象返回。
/// </summary>
/// <param name="bitmap"></param>
/// <returns></returns>
public static Region OpaquePixels(Bitmap bitmap)
{
Region r = new Region();
r.MakeEmpty();
for (int i = 0; i < bitmap.Width; i++)
for (int j = 0; j < bitmap.Height; j++)
if (bitmap.GetPixel(i, j).A != (byte)0)
r.Union(new Rectangle(i, j, 1, 1));
return r;
}