生成缩略图和添加水印

using System.IO;
using System.Drawing.Imaging;
using System.Drawing;
using System.Collections;

 /// <summary>
    /// 生成缩略图
    /// </summary>
    /// <param name="Width">缩略图的宽度</param>
    /// <param name="Height">缩略图的高度</param>
    /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>
    /// <returns>成功返回true，否则返回false</returns>
    public bool GetReducedImage(int Width, int Height, string ImageFileName, string targetFilePath)
    {

        System.Drawing.Image ReducedImage = System.Drawing.Image.FromFile(ImageFileName);
        //新建一个bmp图片
        System.Drawing.Image bitmap = new System.Drawing.Bitmap(Width, Height);

        //新建一个画板
        Graphics g = System.Drawing.Graphics.FromImage(bitmap);

        //设置高质量插值法
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

        //设置高质量,低速度呈现平滑程度
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

        //清空画布并以透明背景色填充
        g.Clear(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(ReducedImage, new Rectangle(0, 0, Width, Height),
            new Rectangle(0, 0, ReducedImage.Width, ReducedImage.Height),
            GraphicsUnit.Pixel);

        try
        {
            //以jpg格式保存缩略图
            bitmap.Save(targetFilePath, System.Drawing.Imaging.ImageFormat.Jpeg);
            return true;
        }
        catch (System.Exception e)
        {
            throw e;
        }
        finally
        {
            ReducedImage.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }

  /// <summary>
    /// 给图片添加文字水印
    /// </summary>
    /// <param name="str_sourceImagePath"></param>
    /// <param name="str_WaterImagePatgh"></param>
    /// <param name="str_SaveImagePath"></param>
    public void AddWaterImage(string str_sourceImagePath, string str_WaterImagePatgh, string str_SaveImagePath)
    {
        System.Drawing.Image Cover;
        if (File.Exists(str_sourceImagePath))
        {
            //加载图片
            Cover = System.Drawing.Image.FromFile(str_sourceImagePath);
            //加载水印图片
            System.Drawing.Image watermark = System.Drawing.Image.FromFile(str_WaterImagePatgh);
            //实例化画布
            Graphics g = Graphics.FromImage(Cover);

            //在image上绘制水印
            g.DrawImage(watermark, new Rectangle(Cover.Width - watermark.Width, Cover.Height - watermark.Height, watermark.Width, watermark.Height), 0, 0, watermark.Width, watermark.Height, GraphicsUnit.Pixel);
            //释放画布
            g.Dispose();
            //释放水印图片
            watermark.Dispose();

            //将修改的图片保存到输出流中
            Cover.Save(str_SaveImagePath, ImageFormat.Jpeg);

            Cover.Dispose();
        }

    }

    /// <summary>
    /// 检测扩展名的有效性
    /// </summary>
    /// <param name="sExt">文件名扩展名</param>
    /// <returns>如果扩展名有效,返回true,否则返回false.</returns>
    private bool CheckValidExt(string sExt)
    {
        bool flag = false;
        string[] aExt = AllowExt.Split('|');
        foreach (string filetype in aExt)
        {
            if (filetype.ToLower() == sExt.ToLower())
            {
                flag = true;
                break;
            }
        }
        return flag;
    }