winform双缓冲, 从内存画图到到picturebox

 base.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);

private Image DrawImage(string strFilePath)

        {
            try
            {
                Bitmap bitmap = new Bitmap(strFilePath);
                //如果原图片是索引像素格式之列的，则需要转换
                if (IsPixelFormatIndexed(bitmap.PixelFormat))
                {
                    Bitmap bmp = new Bitmap(bitmap.Width, bitmap.Height, PixelFormat.Format32bppArgb);
                    using (Graphics g = Graphics.FromImage(bmp))
                    {
                        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                        g.DrawImage(bitmap, 0, 0);
                        Pen pen = new Pen(Color.Red, 3);
                        for (int i = 0; i < bitmap.Width; i += bitmap.Width / 4)
                        {
                            g.DrawLine(pen, i, 0, i, bitmap.Height);
                        }
                        for (int i = 0; i < bitmap.Height; i += bitmap.Height / 4)
                        {
                            g.DrawLine(pen, 0, i, bitmap.Width, i);
                        }
                    }
                }
                else
                {
                    Graphics g = Graphics.FromImage(bitmap);
                    g.DrawImage(bitmap, bitmap.Width, bitmap.Height);
                    Pen pen = new Pen(Color.Red, 3);
                    for (int i = 0; i < bitmap.Width; i += bitmap.Width / 4)
                    {
                        g.DrawLine(pen, i, 0, i, bitmap.Height);
                    }
                    for (int i = 0; i < bitmap.Height; i += bitmap.Height / 4)
                    {
                        g.DrawLine(pen, 0, i, bitmap.Width, i);
                    }
                }
                return bitmap;
            }
            catch { return null; }
        }

   /// <summary>
        /// 会产生graphics异常的PixelFormat
        /// </summary>
        private static PixelFormat[] indexedPixelFormats = { PixelFormat.Undefined, PixelFormat.DontCare,
            PixelFormat.Format16bppArgb1555, PixelFormat.Format1bppIndexed, PixelFormat.Format4bppIndexed,
            PixelFormat.Format8bppIndexed
        };
        /// <summary>
        /// 判断图片的PixelFormat 是否在 引发异常的 PixelFormat 之中
        /// </summary>
        /// <param name="imgPixelFormat">原图片的PixelFormat</param>
        /// <returns></returns>
        private static bool IsPixelFormatIndexed(PixelFormat imgPixelFormat)
        {
            foreach (PixelFormat pf in indexedPixelFormats)
            {
                if (pf.Equals(imgPixelFormat)) return true;
            }

            return false;

        }

下面这个函数从内存画图到picbox, 因为有些图片是索引色, 所以先鉴定了下图片. 画图时用线画了格子. 不用时可以去了.