asp.net修改图片的大小

/// <summary>
/// 修改指定图片的分辨率
/// </summary>
/// <param name="fileFoldUrl">文件夹url</param>
/// <param name="fileName">文件名</param>
/// <param name="filePath">文件路径，带文件名</param>
/// <param name="_width">分辨率的宽</param>
/// <param name="_height">分辨率的高</param>
public void update_picture(string fileFoldUrl, string fileName, string filePath, int _width, int _height)
{
    byte[] zp = this.load_pictMemory(filePath);

    MemoryStream ms = new MemoryStream(zp);

    System.Drawing.Image img = System.Drawing.Image.FromStream(ms);

    Bitmap btp = new Bitmap(img, _width, _height);

    DirectoryInfo dti = new DirectoryInfo(fileFoldUrl);

    FileInfo[] fis = dti.GetFiles();

    string fileUrl = fileFoldUrl + fileName;

    btp.Save(fileUrl);
}

/// <summary>
/// 获取指定文件流的字节大小
/// </summary>
/// <param name="filePath">文件路径</param>
/// <returns>byte[]</returns>
public byte[] load_pictMemory(string filePath)
{
    byte[] pictData = null;

    FileInfo fi = new FileInfo (filePath);

    if (fi.Exists)
    {
        pictData = new byte[fi.Length];

        FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.ReadWrite);

        BinaryReader br = new BinaryReader(fs);

        br.Read(pictData, 0, Convert.ToInt32(fi.Length));

        fs.Dispose();
    }
    else
    {
        HttpContext.Current.Response.Write("<script language='javascript'>alert('没有找到你所指定的图片')</script>");
    }
    return pictData;
}