C# 降低图片的质量

        /// <summary>
        /// 压缩图片
        /// </summary>
        /// <param name="filePath">要压缩的图片的路径</param>
        /// <param name="newfilePath">压缩后的图片的路径</param>
        public void ChangeImageSize(string filePath, string newfilePath)
        {
            Bitmap bmp = null;
            ImageCodecInfo ici = null;
            System.Drawing.Imaging.Encoder ecd = null;
            EncoderParameter ept = null;
            EncoderParameters eptS = null;
            try
            {
                bmp = new Bitmap(filePath);
                ici = this.getImageCoderInfo("image/jpeg");
                ecd = System.Drawing.Imaging.Encoder.Quality;
                eptS = new EncoderParameters(1);
                ept = new EncoderParameter(ecd, 80L);
                eptS.Param[0] = ept;
                bmp.Save(newfilePath, ici, eptS);
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
            finally
            {
                bmp.Dispose();
                ept.Dispose();
                eptS.Dispose();
            }
        }

        /// <summary>
        /// 获取图片编码类型信息
        /// </summary>
        /// <param name="coderType">编码类型</param>
        /// <returns>ImageCodecInfo</returns>
        private ImageCodecInfo getImageCoderInfo(string coderType)
        {
            ImageCodecInfo[] iciS = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo retIci = null;
            foreach (ImageCodecInfo ici in iciS)
            {
                if (ici.MimeType.Equals(coderType))
                    retIci = ici;
            }
            return retIci;
        }