C#创建缩略图操作类实例

本文实例讲述了c#创建缩略图操作类。分享给大家供大家参考。具体分析如下：

这个c#类可以生成各种形式的缩略图，可以自动保持图片比例缩略，可以根据百分比获得图片尺寸等

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();
  }
 }
}

希望本文所述对大家的c#程序设计有所帮助。