C#5种方式生成缩略图

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

namespace MyTest
{
    class imgThumbnail
    {
        public enum mode
        {
            W,
            H,
            HW,
            Cut,
            MaxHW
        }
        public imgThumbnail()
        {

        }
        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath">源图路径（物理路径）</param>
        /// <param name="thumbnailPath">缩略图路径（物理路径）</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="mode">生成缩略图的方式</param>    
        public static Image MakeThumbnail(string originalImagePath, int width, int height, mode m)
        {
            if (!File.Exists(originalImagePath))
            {
                return null;
            }
            Image originalImage = Image.FromFile(originalImagePath);

            int towidth = width;
            int toheight = height;

            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;

            switch (m)
            {
                case mode.MaxHW:
                    if ((ow / width) > (ow / height))
                    {
                        towidth = width;
                        toheight = (Int32)Math.Ceiling(Convert.ToDecimal((oh * towidth) / ow));
                        if (toheight > height)
                        {
                            towidth = Convert.ToInt32(towidth * (Convert.ToDecimal(height) / toheight));
                            toheight = height;
                        }
                    }
                    else
                    {
                        toheight = height;
                        towidth = (Convert.ToInt32(Math.Ceiling(Convert.ToDecimal(ow * toheight)) / oh));
                        if (towidth > width)
                        {
                            toheight = Convert.ToInt32(toheight * Convert.ToDecimal(width) / towidth);
                            towidth = width;
                        }
                    }
                    break;
                case mode.HW://指定高宽缩放（可能变形）                
                    break;
                case mode.W://指定宽，高按比例                    
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case mode.H://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case mode.Cut://指定高宽裁减（不变形）                
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                default:
                    break;
            }

            towidth = towidth > ow ? ow : towidth;
            toheight = toheight > oh ? oh : toheight;
            if (toheight == 0 || towidth == 0)
            {
                return null;
            }
            //新建一个bmp图片
            Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            //新建一个画板
            Graphics g = System.Drawing.Graphics.FromImage(bitmap);

            //设置高质量插值法
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            //设置高质量,低速度呈现平滑程度
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //清空画布并以透明背景色填充
            g.Clear(Color.Transparent);

            //在指定位置并且按指定大小绘制原图片的指定部分
            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
                new Rectangle(x, y, ow, oh),
                GraphicsUnit.Pixel);

            try
            {
                return bitmap;
                //以jpg格式保存缩略图
                //bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (System.Exception e)
            {
                return null;
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                //bitmap.Dispose();
                g.Dispose();
            }
        }
    }
}