C#生成缩略图

很多时候。用户上传一张图片。需要生成不同尺寸的缩略图，当然。缩略图不能大于当前上传的图像。否则分辨率变了。头像就不清晰了

下面附上代码。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;

namespace ADO.net01
{
    class Program
    {
        static void Main(string[] args)
        {
            //获取图片路径
            string y = System.AppDomain.CurrentDomain.BaseDirectory;
            string img = y + "1.jpg";

            Bitmap r = CreateThumbnail(img, 20, 50);
            r.Save(y + "12.jpg"); //保存缩略图
        }
        //Bitmap所属命名空间 system.Drawing

        /// <summary>
        /// 
        /// </summary>
        /// <param name="lcFilename">需要改变大小的图片位置</param>
        /// <param name="lnWidth">缩略图的宽度</param>
        /// <param name="lnHeight">缩略图的高度</param>
        /// <returns></returns>
        public static Bitmap CreateThumbnail(string lcFilename, int lnWidth, int lnHeight)
        {
            System.Drawing.Bitmap bmpOut = null;
            try
            {
                Bitmap loBMP = new Bitmap(lcFilename);
                ImageFormat loFormat = loBMP.RawFormat;

                decimal lnRatio;
                int lnNewWidth = 0;
                int lnNewHeight = 0;

                //如果图像小于缩略图直接返回原图，因为upfront
                if (loBMP.Width < lnWidth && loBMP.Height < lnHeight)
                    return loBMP;

                if (loBMP.Width > loBMP.Height)
                {
                    lnRatio = (decimal)lnWidth / loBMP.Width;
                    lnNewWidth = lnWidth;
                    decimal lnTemp = loBMP.Height * lnRatio;
                    lnNewHeight = (int)lnTemp;
                }
                else
                {
                    lnRatio = (decimal)lnHeight / loBMP.Height;
                    lnNewHeight = lnHeight;
                    decimal lnTemp = loBMP.Width * lnRatio;
                    lnNewWidth = (int)lnTemp;
                }
                bmpOut = new Bitmap(lnNewWidth, lnNewHeight);
                Graphics g = Graphics.FromImage(bmpOut);
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                g.FillRectangle(Brushes.White, 0, 0, lnNewWidth, lnNewHeight);
                g.DrawImage(loBMP, 0, 0, lnNewWidth, lnNewHeight);

                loBMP.Dispose();
            }
            catch
            {
                return null;
            }

            return bmpOut;
        }
    }
}

运行项目后。成功的生成了缩略图