CSharp修改图片质量

/// <summary>
        /// 保存JPG时用
        /// </summary>
        /// <param name="mimeType"></param>
        /// <returns>得到指定mimeType的ImageCodecInfo</returns>
        private static ImageCodecInfo GetCodecInfo(string mimeType)
        {
            ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
            foreach (ImageCodecInfo ici in CodecInfo)
            {
                if (ici.MimeType == mimeType) return ici;
            }
            return null;
        }
         
        /// <summary>
        /// 保存为JPEG格式，支持压缩质量选项
        /// </summary>
        /// <param name="bmp"></param>
        /// <param name="FileName"></param>
        /// <param name="Qty"></param>
        /// <returns></returns>
        public static Bitmap KiSaveAsJPEG(Bitmap bmp, int Qty)
        {
            try
            {
                EncoderParameter p;
                EncoderParameters ps;
 
                ps = new EncoderParameters(1);
 
                p = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, Qty);
                ps.Param[0] = p;
                MemoryStream ms = new MemoryStream();
                bmp.Save(ms, GetCodecInfo("image/jpeg"), ps);
 
                return new Bitmap(ms); ;
            }
            catch
            {
                return null;
            }
 
        }