C#实现生成指定图片的缩略图

//制作缩略图（压缩图），可接收两种参数，物理路径文件 originalImagePath 或 Byte[]型数据 bvalue，两者同时传递以物理路径文件优先。
//方法返回压缩后的 Byte[]数组数据，如果同时指定输出文件路径thumbnailPath，则同时生成这个文件。
//指定输出缩略图的宽width和高height，如果为0，则默认为原图的宽或高
//mode为压缩方法："HW":指定高宽缩放（可能变形）,"W":指定宽，高按比例 ,"H":指定高，宽按比例 , "Cut":指定高宽裁减（不变形）
 
public  Byte[] MakeThumbnail(string originalImagePath, Byte[] bvalue, string thumbnailPath, int width=0, int height=0, string mode="Cut", System.Drawing.Drawing2D.InterpolationMode interpolationMode= System.Drawing.Drawing2D.InterpolationMode.High)
{
                System.Drawing.Image originalImage;
                if (originalImagePath != "")
                {
                    originalImage = System.Drawing.Image.FromFile(originalImagePath);
                }
                else
                {
                    originalImage = System.Drawing.Image.FromStream(new System.IO.MemoryStream(bvalue));
                }
 
                int towidth = width;
                int toheight = height;
 
                int x = 0;
                int y = 0;
                int ow = originalImage.Width;
                int oh = originalImage.Height;
 
                if (towidth == 0)
                {
                    towidth = ow;
                }
                if (toheight == 0)
                {
                    toheight = oh;
                }
 
                switch (mode)
                {
                    case "HW"://指定高宽缩放（可能变形）                 
                        break;
                    case "W"://指定宽，高按比例                     
                        toheight = originalImage.Height * towidth / originalImage.Width;
                        break;
                    case "H"://指定高，宽按比例 
                        towidth = originalImage.Width * toheight / originalImage.Height;
                        break;
                    case "Cut"://指定高宽裁减（不变形）                 
                        if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                        {
                            oh = originalImage.Height;
                            ow = originalImage.Height * towidth / toheight;
                            y = 0;
                            x = (originalImage.Width - ow) / 2;
                        }
                        else
                        {
                            ow = originalImage.Width;
                            oh = originalImage.Width * toheight / towidth;
                            x = 0;
                            y = (originalImage.Height - oh) / 2;
                        }
                        break;
                    default:
                        break;
                }
                //新建一个bmp图片 
                System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
 
                //新建一个画板 
                System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
 
                //设置高质量插值法 
                g.InterpolationMode = interpolationMode ;
 
                //设置高质量,低速度呈现平滑程度 
                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
 
                //清空画布并以透明背景色填充 
                g.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 
                g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
                    new System.Drawing.Rectangle(x, y, ow, oh),
                    System.Drawing.GraphicsUnit.Pixel);
 
 
                try
                {
                    //以jpg格式保存缩略图 
                    System.IO.MemoryStream mstream = new System.IO.MemoryStream();
                    System.Drawing.Imaging.ImageFormat format = originalImage.RawFormat;
                    System.Drawing.Imaging.ImageFormat toFormat = System.Drawing.Imaging.ImageFormat.Jpeg;
                    if (format.Equals(System.Drawing.Imaging.ImageFormat.Jpeg))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Jpeg;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Png))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Png;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Bmp))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Bmp;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Gif))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Gif;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Icon))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Icon;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Emf))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Emf;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Exif))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Exif;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Tiff))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Tiff;
                    }
                    else if (format.Equals(System.Drawing.Imaging.ImageFormat.Wmf))
                    {
                        toFormat = System.Drawing.Imaging.ImageFormat.Wmf;
                    }
 
                    bitmap.Save(mstream, toFormat);
                    
                    byte[] byData = new Byte[mstream.Length];
                    mstream.Position = 0;
                    mstream.Read(byData, 0, byData.Length);
                    mstream.Close();
                    if (thumbnailPath != "")
                    {
                        bitmap.Save(thumbnailPath, toFormat);
                    }
                    return byData;
                }
                catch (System.Exception e)
                {
                    throw e;
                }
                finally
                {
                    originalImage.Dispose();
                    bitmap.Dispose();
                    g.Dispose();
                }
}

string upfilename = Request.PhysicalApplicationPath + "\\upload.jpg"; //上传的图片路径
string mtfilename = Request.PhysicalApplicationPath + "\\mt.jpg";  //缩略图的图片路径
if (System.IO.File.Exists(upfilename))
{
    FileInfo fileInfo = new FileInfo(upfilename);
    float _fsize = fileInfo.Length / (1024*1024);
    if (_fsize >= 2)
    {
        MakeThumbnail(upfilename, null, mtfilename);
    }
    else
    {
        mtfilename = upfilename;
    }
    Response.Write("Result Filename is :"+mtfilename);
}