C#控制生成图片的大小

        private void button1_Click(object sender, EventArgs e)
        {
            using (Bitmap bitmap = new Bitmap("d:\\a.jpg"))
            {
                string f = string.Format("d:\\{0}.jpg", Guid.NewGuid());
                KiSaveAsJPEG(bitmap, f, (int)this.numericUpDown1.Value);
            }
        }

        /**/
        /// <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 bool KiSaveAsJPEG(Bitmap bmp, string FileName, int Qty)
        {
            try
            {
                EncoderParameter p;
                EncoderParameters ps;
                ps = new EncoderParameters();
                p = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, Qty);
                ps.Param[] = p;
                bmp.Save(FileName, GetCodecInfo("image/jpeg"), ps);
                return true;
            }
            catch
            {
                return false;
            }

        }

Qty代表质量等级：90代表90%.