C#图片处理，缩略图制作

准备参数：图片文件流、文件名

方法：1.先将图片流通过System.Drawing.Image.FromStream方法转成图片对象

　　　2.通过图片对象.GetThumbnailImage方法生成自定义长宽的缩略图。

生成方法：

缩略图生成：

/// <summary>
    /// 缩略图
    /// shidd
    /// </summary>
    /// <param name="myStream">文件流</param>
    /// <param name="serverUrl">文件名</param>
    /// <returns>字节数组</returns>
    private byte[] toImage(Stream myStream, string serverUrl)
    {
        //生成缩略图
        //创建改变后的Stream
        var stream = new System.IO.MemoryStream();
        //取得后缀名
        string suffix = serverUrl.Substring(serverUrl.LastIndexOf("."));
        //创建一个图像对象取得上传图片对象
        System.Drawing.Image myImage = System.Drawing.Image.FromStream(myStream, false);
        //int percentage= myImage.Height / myImage.Width;//原图片比例
        //由上传图片产生一个缩略图(600*400)
        System.Drawing.Image thumbImage = myImage.GetThumbnailImage(600, 400, null, System.IntPtr.Zero);
        //保存缩略图到Stream流
        thumbImage.Save(stream, this.getImageFormat(suffix));
        //关闭缩略图对象
        thumbImage.Dispose();
        return stream.ToArray();
    }

图片格式：

 /// <summary>
    /// 图片格式
    /// </summary>
    /// <param name="suffix">文件后缀</param>
    /// <returns></returns>
    private System.Drawing.Imaging.ImageFormat getImageFormat(string suffix)
    {
        System.Drawing.Imaging.ImageFormat myFormat;
        switch (suffix.ToLower())
        {
            case ".bmp":
                myFormat = System.Drawing.Imaging.ImageFormat.Bmp;
                break;
            case ".emf":
                myFormat = System.Drawing.Imaging.ImageFormat.Emf;
                break;
            case ".exif":
                myFormat = System.Drawing.Imaging.ImageFormat.Exif;
                break;
            case ".gif":
                myFormat = System.Drawing.Imaging.ImageFormat.Gif;
                break;
            case ".icon":
                myFormat = System.Drawing.Imaging.ImageFormat.Icon;
                break;
            case ".jpeg":
            case ".jpg":
                myFormat = System.Drawing.Imaging.ImageFormat.Jpeg;
                break;
            case ".png":
                myFormat = System.Drawing.Imaging.ImageFormat.Png;
                break;
            case ".tiff":
                myFormat = System.Drawing.Imaging.ImageFormat.Tiff;
                break;
            case ".wmf":
                myFormat = System.Drawing.Imaging.ImageFormat.Wmf;
                break;
            default:
                myFormat = System.Drawing.Imaging.ImageFormat.MemoryBmp;
                break;
        }
        return (myFormat);
    }

调用：

 //调用缩略图方法
                        bytes = toImage(ms, ServerUrl);

GIF图缩略（注：缩略后图片不能动了，求高手指点）

 // <summary>
    /// 为GIF图片生成缩略图
    /// </summary>
    /// <param name="phyPath">原图片的路径</param>
    /// <param name="width">缩略图宽</param>
    /// <param name="height">缩略图高</param>
    /// <returns></returns>
    public byte[] GetThumbnail(Stream myStream, int width, int height)
    {
        //创建改变后的Stream
        var stream = new System.IO.MemoryStream();
        //创建一个图像对象取得上传图片对象
        System.Drawing.Image myImage = System.Drawing.Image.FromStream(myStream, false);
        System.Drawing.Bitmap bmp = new System.Drawing.Bitmap(width, height);
        //从Bitmap创建一个System.Drawing.Graphics
        System.Drawing.Graphics gr = System.Drawing.Graphics.FromImage(bmp);
        //设置
        gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        //下面这个也设成高质量
        gr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
        //下面这个设成High
        gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
        //把原始图像绘制成上面所设置宽高的缩小图
        System.Drawing.Rectangle rectDestination = new System.Drawing.Rectangle(0, 0, width, height);

        gr.DrawImage(myImage, rectDestination, 0, 0, myImage.Width, myImage.Height, System.Drawing.GraphicsUnit.Pixel);
        myImage.Save(stream, System.Drawing.Imaging.ImageFormat.Jpeg);
        return stream.ToArray();
    }