private

 

void

 fileUpload_Click(

object

 sender, System.EventArgs e)

        

{

            // 模拟数据库里取出byte[]再显示缩略,

            // 模拟方法：先上传，把stream转成byte[],再把byte[]放在stream里,再输出

            // 上传

            System.IO.Stream fs = jpgUpload.PostedFile.InputStream;

            int nBytes          = jpgUpload.PostedFile.ContentLength;

            byte[] ByteArray    = new byte[nBytes];

            int nBytesRead      = fs.Read(ByteArray, 0, nBytes);

            MemoryStream mBytes  = new MemoryStream(ByteArray,0,nBytes);

            

            // 转为stream,处理缩略

            System.Drawing.Image _img;

            _img = System.Drawing.Image.FromStream(mBytes);

            System.Drawing.Image _thumbImg = _img.GetThumbnailImage(Convert.ToInt32(_img.Width* 0.3),Convert.ToInt32( _img.Height * 0.3),null, IntPtr.Zero);

            // 显示到客户端

            Response.ContentType    = this.jpgUpload.PostedFile.ContentType;

            MemoryStream MemStream  = new MemoryStream(); 

            _thumbImg.Save(MemStream, System.Drawing.Imaging.ImageFormat.Jpeg); 

            MemStream.WriteTo(Response.OutputStream); 

            Response.Flush();

        }

注释都在里面，不用说明了吧，重要的是GetThumbnailImage这个方法.