C#上传下载图片

1.首先我们通过流来上传下载图片，所有操作只停留在流这一层

  MemoryStream ms;
        //左侧按钮
        private void button1_Click(object sender, EventArgs e)
        {       
            ms = new MemoryStream();
            Image bi =pictureBox1.Image;
            bi.Save(ms, pictureBox1.Image.RawFormat);//将图片存入流中    
        }
        //右侧按钮
        private void button2_Click(object sender, EventArgs e)
        {
            Image img = Image.FromStream(ms, true);
            pictureBox2.Image = img;  
            ms.Close();      
        }

分别点击左侧和右侧按钮，则将左侧图片加载到右侧：（PictureBox的SizeMode属性可以设置图片的填充方式）

2.通过将图片转化为流然后转化为字节；将字节转化为流，然后加载图片

     图片转化为字节的代码：

   public static byte[] ImgToByte(Image img, System.Drawing.Imaging.ImageFormat imgFormat)
        {
            Bitmap bmp = new Bitmap(img);
            MemoryStream memStream = new MemoryStream();
            bmp.Save(memStream, imgFormat);
            memStream.Seek(0, SeekOrigin.Begin); //及时定位流的开始位置
            byte[] btImage = new byte[memStream.Length];
            memStream.Read(btImage, 0, btImage.Length);
            memStream.Close();
            return btImage;
        }

    字节转化为图片的代码：

  public static Image ByteToImg(byte[] btImage)
        {
            MemoryStream memStream = new MemoryStream();
            //Stream memStream = null;
            memStream.Write(btImage, 0, btImage.Length);
            memStream.Position = 0;
            memStream.Seek(0, SeekOrigin.Begin);
            //Bitmap bmp = new Bitmap(memStream, true);
            Image img;
            try
            {
                img = Image.FromStream(memStream, true);
                memStream.Close();
                //img = new Bitmap(memStream);
            }
            catch (Exception ex)
            {
                img = null;
                MessageBox.Show(ex + "");
            }
            finally
            {
                memStream.Close();
            }
            return img;
        }