求大神帮忙，我读取一张图片，想修改大小保存到另个文件夹中，报错
关键代码如下：

    public static void MakeThumNail(string originalImagePath, string thumNailPath, int width, int height, string model)

    {

        System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);



        int thumWidth = width; //缩略图的宽度

        int thumHeight = height; //缩略图的高度



        int x = 0;

        int y = 0;



        int originalWidth = originalImage.Width; //原始图片的宽度

        int originalHeight = originalImage.Height; //原始图片的高度



        switch (model)

        {

            case "HW": //指定高宽缩放,可能变形

                break;

            case "W": //指定宽度,高度按照比例缩放

                thumHeight = originalImage.Height * width / originalImage.Width;

                break;

            case "H": //指定高度,宽度按照等比例缩放

                thumWidth = originalImage.Width * height / originalImage.Height;

                break;

            case "Cut":

                if ((double)originalImage.Width / (double)originalImage.Height > (double)thumWidth / (double)thumHeight)

                {

                    originalHeight = originalImage.Height;

                    originalWidth = originalImage.Height * thumWidth / thumHeight;

                    y = 0;

                    x = (originalImage.Width - originalWidth) / 2;

                }

                else

                {

                    originalWidth = originalImage.Width;

                    originalHeight = originalWidth * height / thumWidth;

                    x = 0;

                    y = (originalImage.Height - originalHeight) / 2;

                }

                break;

            default:

                break;

        }



        //新建一个bmp图片

        System.Drawing.Image bitmap = new System.Drawing.Bitmap(thumWidth, thumHeight);



        //新建一个画板

        System.Drawing.Graphics graphic = System.Drawing.Graphics.FromImage(bitmap);



        //设置高质量查值法

        graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;



        //设置高质量，低速度呈现平滑程度

        graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;



        //清空画布并以透明背景色填充

        graphic.Clear(System.Drawing.Color.Transparent);



        //在指定位置并且按指定大小绘制原图片的指定部分

        graphic.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, thumWidth, thumHeight),

                          new System.Drawing.Rectangle(x, y, originalWidth, originalHeight),

                          System.Drawing.GraphicsUnit.Pixel);

        try

        {

            if (!Directory.Exists(thumNailPath))

            {

                Directory.CreateDirectory(thumNailPath);

            }

            bitmap.Save(thumNailPath, System.Drawing.Imaging.ImageFormat.Jpeg);



        }

        catch (Exception ex)

        {

            throw ex;

        }

        finally

        {

            originalImage.Dispose();

            bitmap.Dispose();

            graphic.Dispose();

        }

    }

bitmap.Save(thumNailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
就是到这一句，就产生错误，GDI+ 中发生一般性错误。

去拜读和骨骼都查了，有的说没权限，有的说没释放，但是我个人还是认为是没释放，求大神帮忙看下