一个自定义的C#图片处理类，用于生成缩略图信息

using System;
using System.Drawing.Imaging;
using System.Collections;
using System.Drawing;
using System.IO;
 
namespace DotNet.Utilities
{
    /// <summary>
    /// 枚举,生成缩略图模式
    /// </summary>
    public enum ThumbnailMod : byte
    {
        /// <summary>
        /// HW
        /// </summary>
        HW,/// <summary>
        /// W
        /// </summary>
        W,/// <summary>
        /// H
        /// </summary>
        H,/// <summary>
        /// Cut
        /// </summary>
        Cut
    };
 
    /// <summary>
    /// 操作图片类,生成缩略图,添加水印
    /// </summary>
    public static class PicDeal
    {
        private static Hashtable htmimes = new Hashtable();
        internal static readonly string AllowExt = ".jpe|.jpeg|.jpg|.png|.tif|.tiff|.bmp";
        #region 生成缩略图
        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath"></param>
        /// <param name="width"></param>
        /// <param name="height"></param>
        /// <param name="mode"></param>
        /// <returns></returns>
        public static bool MakeThumbnail(string originalImagePath,int width,int height,ThumbnailMod mode)
        {
            string thumbnailPath = originalImagePath.Substring(0,originalImagePath.LastIndexOf('.')) + "s.jpg";
            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 (mode)
            {
                case ThumbnailMod.HW://指定高宽缩放（可能变形）               
                    break;
                case ThumbnailMod.W://指定宽，高按比例                   
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case ThumbnailMod.H://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case ThumbnailMod.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;
            }
 
            //新建一个bmp图片
            Image bitmap = new Bitmap(towidth,toheight);
 
            //新建一个画板
            Graphics g = 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(System.Drawing.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,towidth,toheight),new Rectangle(x,y,ow,oh),GraphicsUnit.Pixel);
            bool isok = false;
            try
            {
                //以jpg格式保存缩略图
                bitmap.Save(thumbnailPath,ImageFormat.Jpeg);
                isok = true;
            }
            catch (Exception)
            {
                thumbnailPath = originalImagePath;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
            return isok;
        }
        #endregion
 
        #region 在图片上生成图片水印
        ///// <summary>
        ///// 在图片上生成图片水印
        ///// </summary>
        ///// <param name="Path">原服务器图片路径</param>
        ///// <param name="Path_syp">生成的带图片水印的图片路径</param>
        ///// <param name="Path_sypf">水印图片路径</param>
        /// <summary>
        /// 在图片上生成图片水印
        /// </summary>
        /// <param name="Path">原服务器图片路径</param>
        /// <param name="Path_sypf">水印图片路径</param>
        public static void AddWaterPic(string Path,string Path_sypf)
        {
            try
            {
                Image image = Image.FromFile(Path);
                Image copyImage = Image.FromFile(Path_sypf);
                Graphics g = Graphics.FromImage(image);
                g.DrawImage(copyImage,new System.Drawing.Rectangle(image.Width - copyImage.Width,image.Height - copyImage.Height,copyImage.Width,copyImage.Height),copyImage.Height,System.Drawing.GraphicsUnit.Pixel);
                g.Dispose();
 
                image.Save(Path + ".temp");
                image.Dispose();
                System.IO.File.Delete(Path);
                File.Move(Path + ".temp",Path);
            }
            catch
            { }
        }
        #endregion
 
        /// <summary>
        /// 公共方法
        /// </summary>
        private static void GetImgType()
        {
            htmimes[".jpe"] = "image/jpeg";
            htmimes[".jpeg"] = "image/jpeg";
            htmimes[".jpg"] = "image/jpeg";
            htmimes[".png"] = "image/png";
            htmimes[".tif"] = "image/tiff";
            htmimes[".tiff"] = "image/tiff";
            htmimes[".bmp"] = "image/bmp";
        }
 
 
        #region 返回新图片尺寸
        /// <summary>
        /// 返回新图片尺寸
        /// </summary>
        /// <param name="width">原始宽</param>
        /// <param name="height">原始高</param>
        /// <param name="maxWidth">新图片最大宽</param>
        /// <param name="maxHeight">新图片最大高</param>
        /// <returns></returns>
        public static Size ResizeImage(int width,int maxWidth,int maxHeight)
        {
            decimal MAX_WIDTH = (decimal)maxWidth;
            decimal MAX_HEIGHT = (decimal)maxHeight;
            decimal ASPECT_RATIO = MAX_WIDTH / MAX_HEIGHT;
 
            int newWidth,newHeight;
 
            decimal originalWidth = (decimal)width;
            decimal originalHeight = (decimal)height;
 
            if (originalWidth > MAX_WIDTH || originalHeight > MAX_HEIGHT)
            {
                decimal factor;
                // determine the largest factor
                if (originalWidth / originalHeight > ASPECT_RATIO)
                {
                    factor = originalWidth / MAX_WIDTH;
                    newWidth = Convert.ToInt32(originalWidth / factor);
                    newHeight = Convert.ToInt32(originalHeight / factor);
                }
                else
                {
                    factor = originalHeight / MAX_HEIGHT;
                    newWidth = Convert.ToInt32(originalWidth / factor);
                    newHeight = Convert.ToInt32(originalHeight / factor);
                }
            }
            else
            {
                newWidth = width;
                newHeight = height;
            }
 
            return new Size(newWidth,newHeight);
 
        }
        #endregion
    }
}