C#创建缩略图的操作类代码

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
namespace HtmlSnap
{
    public static class ImageHelper
    {

    /// <summary>
    /// 获取缩略图
    /// </summary>
    /// <param name="image"></param>
    /// <param name="width"></param>
    /// <param name="height"></param>
    /// <returns></returns>
    public static Image GetThumbnailImage(Image image, int width, int height)
    {
        if (image == null || width < 1 || height < 1)
            return null;

        // 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.HighQualityBicubic;

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

            // 高质量、低速度复合
            //
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.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(image, new Rectangle(0, 0, width, height),
                new Rectangle(0, 0, image.Width, image.Height),
                GraphicsUnit.Pixel);

            return bitmap;
        }
    }

    /// <summary>
    /// 生成缩略图，并保持纵横比
    /// </summary>
    /// <param name="image"></param>
    /// <param name="width"></param>
    /// <param name="height"></param>
    /// <returns>生成缩略图后对象</returns>
    public static Image GetThumbnailImageKeepRatio(Image image, int width, int height)
    {
        Size imageSize = GetImageSize(image, width, height);
        return GetThumbnailImage(image, imageSize.Width, imageSize.Height);
    }

    /// <summary>
    /// 根据百分比获取图片的尺寸
    /// </summary>
    /// <param name="picture"></param>
    /// <param name="percent"></param>
    /// <returns></returns>
    public static Size GetImageSize(Image picture, int percent)
    {
        if (picture == null || percent < 1)
            return Size.Empty;

        int width = picture.Width * percent / 100;
        int height = picture.Height * percent / 100;

        return GetImageSize(picture, width, height);
    }

    /// <summary>
    /// 根据设定的大小返回图片的大小，考虑图片长宽的比例问题
    /// </summary>
    /// <param name="picture"></param>
    /// <param name="width"></param>
    /// <param name="height"></param>
    /// <returns></returns>
    public static Size GetImageSize(Image picture, int width, int height)
    {
        if (picture == null || width < 1 || height < 1)
            return Size.Empty;

        Size imageSize;

        imageSize = new Size(width, height);

        double heightRatio = (double)picture.Height / picture.Width;
        double widthRatio = (double)picture.Width / picture.Height;

        int desiredHeight = imageSize.Height;
        int desiredWidth = imageSize.Width;


        imageSize.Height = desiredHeight;
        if (widthRatio > 0)
            imageSize.Width = Convert.ToInt32(imageSize.Height * widthRatio);

        if (imageSize.Width > desiredWidth)
        {
            imageSize.Width = desiredWidth;
            imageSize.Height = Convert.ToInt32(imageSize.Width * heightRatio);
        }

        return imageSize;
    }


    /// <summary>
    /// 获取图像编码解码器的所有相关信息
    /// </summary>
    /// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>
    /// <returns>返回图像编码解码器的所有相关信息</returns>
    public static ImageCodecInfo GetCodecInfo(string mimeType)
    {
        ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
        foreach (ImageCodecInfo ici in CodecInfo)
        {
            if (ici.MimeType == mimeType) return ici;
        }
        return null;
    }

    public static ImageCodecInfo GetImageCodecInfo(ImageFormat format)
    {
        ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();

        foreach (ImageCodecInfo icf in encoders)
        {
            if (icf.FormatID == format.Guid)
            {
                return icf;
            }
        }

        return null;
    }

    public static void SaveImage(Image image, string savePath, ImageFormat format)
    {
        SaveImage(image, savePath, GetImageCodecInfo(format));
    }

    /// <summary>
    /// 高质量保存图片
    /// </summary>
    /// <param name="image"></param>
    /// <param name="savePath"></param>
    /// <param name="ici"></param>
    private static void SaveImage(Image image, string savePath, ImageCodecInfo ici)
    {
        // 设置 原图片 对象的 EncoderParameters 对象
        //
        EncoderParameters parms = new EncoderParameters(1);
        EncoderParameter parm = new EncoderParameter(Encoder.Quality, ((long)95));
        parms.Param[0] = parm;

        image.Save(savePath, ici, parms);
        parms.Dispose();
    }

}
 
}</pre>