c#.net图片裁剪抠图之性能优化

//.net图片裁剪抠图：
1.将不坐标点存入GraphicsPath中；
GraphicsPath gPath = new GraphicsPath();
2.
通常我们判断一个坐标点是否在闭合区间内通采用GraphicsPath.IsVisible(),但事实证明这种方法判断效率及其低，这里我们采用Region.IsVisible(),
经测试，GraphicsPath.IsVisible()处理一张800*800的图片需要14s以上时间。Region.IsVisible()只需要1s.

//
      /// <summary>
      /// 图片截图
      /// </summary>
      /// <param name="bitmap">原图路径</param>
      /// <param name="path">裁剪路径</param>
      /// <returns></returns>
      public static Bitmap BitmapCropGzf(Bitmap bitmap, GraphicsPath path)
      {
          RectangleF rect = path.GetBounds();
          int left = (int)rect.Left;
          int top = (int)rect.Top;
          int width = (int)rect.Width;
          int height = (int)rect.Height;
          //先进行剪裁：
          Bitmap imgCropped = new Bitmap(width, height);
          Graphics objGraphics = Graphics.FromImage(imgCropped);
          objGraphics.Clear(System.Drawing.Color.White);
          int intStartTop = -top;
          int intStartLeft = -left;
          Bitmap b = new Bitmap(bitmap);
          objGraphics.DrawImage(b, intStartLeft, intStartTop);
          b.Dispose();
          objGraphics.Dispose();
          Region r = new Region(path);
          GC.Collect(0);
          for (int i = left; i < left + width; i++)
          {
              for (int j = top; j < top + height; j++)
              {
                  //判断坐标是否在路径中  
                  if (!r.IsVisible(i, j))
                  {
                      imgCropped.SetPixel(i - left, j - top, System.Drawing.Color.Transparent);
                  }
              }
          }
          return imgCropped;
      }