C#图片辅助类，形成缩略图

完善一下别人的方法，成自己好用的工具

using System.Drawing;
using System.Drawing.Imaging;

namespace GXNUQzzx.Tools.Utility
{
    /// <summary>
    /// 图片缩放模式
    /// </summary>
    public enum ScaleMode
    {
        /// <summary>
        /// 指定高宽缩放（可能失真）
        /// </summary>
        Normal,

        /// <summary>
        /// 指定高，宽按比例
        /// </summary>
        Width,

        /// <summary>
        /// 指定宽，高按比例
        /// </summary>
        Height,

        /// <summary>
        /// 指定高宽裁减（不失真）
        /// </summary>
        Cut
    }

    /// <summary>
    /// 图片辅助类
    /// </summary>
    public static class ImageHelper
    {
        /// <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 void GenerateThumbnail(string originalImagePath, string thumbnailPath, int width, int height, ScaleMode mode)
        {
            using (Image originalImage = Image.FromFile(originalImagePath))
            {
                GenerateThumbnail(originalImage, thumbnailPath, width, height, mode);
            }
        }

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImage">源图</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 void GenerateThumbnail(Image originalImage, string thumbnailPath, int width, int height, ScaleMode mode)
        {
            using (Image image = GenerateThumbnail(originalImage, width, height, mode))
            {
                image.Save(thumbnailPath, ImageFormat.Jpeg);
            }
        }

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImage">源图</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>    
        /// <returns>生成的缩略图</returns>
        public static Image GenerateThumbnail(Image originalImage, int width, int height, ScaleMode mode)
        {
            int towidth = width;
            int toheight = height;

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

            #region // 计算缩略图宽高
            switch (mode)
            {
                default:
                case ScaleMode.Normal: { break; }
                case ScaleMode.Height:
                {
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                }
                case ScaleMode.Width:
                {
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                }
                case ScaleMode.Cut:
                {
                    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;
                }
            }
            #endregion

            //新建一个bmp图片
            Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            //新建一个画板
            using (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);
            }

            // 返回生成的缩略图
            return bitmap;
        }

        /// <summary>
        /// 按原像素比例生成一张新图片
        /// </summary>
        /// <param name="oldImagePath">源图片路径（物理路径）</param>
        /// <param name="newImagePath">新图片路径（物理路径）</param>
        public static void GenerateNewImage(string oldImagePath, string newImagePath)
        {
            using (Image originalImage = Image.FromFile(oldImagePath))
            {
                GenerateNewImage(originalImage, newImagePath);
            }
        }

        /// <summary>
        /// 按原像素比例生成一张新图片
        /// </summary>
        /// <param name="oldImage">源图片</param>
        /// <param name="newImagePath">新图片路径（物理路径）</param>
        public static void GenerateNewImage(Image oldImage, string newImagePath)
        {
            using (Image image = GenerateNewImage(oldImage))
            {
                image.Save(newImagePath, ImageFormat.Jpeg);
            }
        }

        /// <summary>
        /// 按原像素比例生成一张新图片
        /// </summary>
        /// <param name="oldImage">源图片</param>
        /// <returns>新图片</returns>
        public static Image GenerateNewImage(Image oldImage)
        {
            int width = oldImage.Width;
            int height = oldImage.Height;

            //新建一个bmp图片
            Image bitmap = new System.Drawing.Bitmap(width, height);

            //新建一个画板
            using (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);

                //创建矩形
                var rectangle = new Rectangle(0, 0, width, height);

                //在指定位置并且按指定大小绘制原图片的指定部分
                g.DrawImage(oldImage, rectangle, rectangle, GraphicsUnit.Pixel);
            }

            // 返回新图片
            return bitmap;
        }
    }
}