C#创建缩略图操作类实例

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();
  }
 }
}