.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;
        }