/// <summary>
/// 取得一个图片中非透明色部分的区域。
/// </summary>
/// <param name="Picture">取其区域的图片。</param>
/// <param name="TransparentColor">透明色。</param>
/// <returns>图片中非透明色部分的区域</returns>
private Region BmpRgn(Bitmap Picture, Color TransparentColor)
{
   int nWidth = Picture.Width;
   int nHeight = Picture.Height;
   Region rgn = new Region();
   rgn.MakeEmpty();
   bool isTransRgn;//前一个点是否在透明区
   Color curColor;//当前点的颜色
   Rectangle curRect = new Rectangle();
   curRect.Height = 1;
   int x = 0, y = 0;
   //逐像素扫描这个图片，找出非透明色部分区域并合并起来。
   for(y = 0; y < nHeight; ++y)
   {
     isTransRgn = true;
     for (x = 0; x < nWidth; ++x)
     {
       curColor = Picture.GetPixel(x,y);
       if(curColor == TransparentColor || x == nWidth - 1)//如果遇到透明色或行尾
          {
            if(isTransRgn == false)//退出有效区
            {
              curRect.Width = x - curRect.X;
              rgn.Union(curRect);
            }
          }
          else//非透明色
          {
            if(isTransRgn == true)//进入有效区
            {
              curRect.X = x;
              curRect.Y = y;
            }
          }//if curColor
          isTransRgn = curColor == TransparentColor;  
       }//for x
     }//for y
     return rgn;
}

this.Region = BmpRgn(new Bitmap("d:\\a.bmp"), Color.FromArgb(0, 0, 0));