tothumbnailimage.aspx.cs

用C#轻松实现缩略图源文件 还不错。大家可以看看的

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Drawing.Imaging;
namespace Exam_C
{
	/// <summary>
	/// ToThumbnailImage 的摘要说明。
	/// </summary>
	public class ToThumbnailImage : System.Web.UI.Page
	{
		/*  
		Create By lion  
		2003-05-20 19:00  
		Copyright (C) 2004 www.LionSky.Net. All rights reserved. 
		Web: http://www.Lionsky.net ;
		Email: [e-mail] 
		*/  


		static Hashtable htmimes=new Hashtable();
		internal readonly string AllowExt = ".jpe|.jpeg|.jpg|.png|.tif|.tiff|.bmp";
		
		#region Web 窗体设计器生成的代码
		override protected void OnInit(EventArgs e)
		{
			#region 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";
			#endregion
			//调用生成缩略图方法
			ToThumbnailImages("lionsky.jpg","b.gif",300);
		}		
		#endregion	

		#region Helper
	
		/// <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>
		static ImageCodecInfo GetCodecInfo(string mimeType)
		{
			ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
			foreach(ImageCodecInfo ici in CodecInfo)
			{
				if(ici.MimeType == mimeType)return ici;
			}
			return null;
		}

		/// <summary>
		/// 检测扩展名的有效性
		/// </summary>
		/// <param name="sExt">文件名扩展名</param>
		/// <returns>如果扩展名有效,返回true,否则返回false.</returns>
		bool CheckValidExt(string sExt)
		{			
			bool flag=false;
			string[] aExt = AllowExt.Split('|');
			foreach(string filetype in aExt)
			{
				if(filetype.ToLower()==sExt)
				{
					flag = true;
					break;
				}
			}			
			return flag;
		}

		/// <summary>
		/// 保存图片
		/// </summary>
		/// <param name="image">Image 对象</param>
		/// <param name="savePath">保存路径</param>
		/// <param name="ici">指定格式的编解码参数</param>
		void SaveImage(System.Drawing.Image image,string savePath,ImageCodecInfo ici)
		{
			//设置 原图片 对象的 EncoderParameters 对象
			EncoderParameters parameters = new EncoderParameters(1);
			parameters.Param[0] = new EncoderParameter(Encoder.Quality, ((long) 90));
			image.Save(savePath, ici, parameters);
			parameters.Dispose();
		}
		#endregion

		#region Methods

		/// <summary>
		/// 生成缩略图
		/// </summary>
		/// <param name="sourceImagePath">原图片路径(相对路径)</param>
		/// <param name="thumbnailImagePath">生成的缩略图路径,如果为空则保存为原图片路径(相对路径)</param>
		/// <param name="thumbnailImageWidth">缩略图的宽度（高度与按源图片比例自动生成）</param>
		public void ToThumbnailImages(string sourceImagePath,string thumbnailImagePath,int thumbnailImageWidth)
		{
			string SourceImagePath = sourceImagePath;
			string ThumbnailImagePath = thumbnailImagePath;
			int ThumbnailImageWidth = thumbnailImageWidth;
			string sExt = SourceImagePath.Substring(SourceImagePath.LastIndexOf(".")).ToLower();
			if(SourceImagePath.ToString()==System.String.Empty) throw new NullReferenceException("SourceImagePath is null!");
			if(!CheckValidExt(sExt))
			{
				throw new ArgumentException("原图片文件格式不正确,支持的格式有[ "+ AllowExt +" ]","SourceImagePath");
			}
			//从 原图片 创建 Image 对象
			System.Drawing.Image image = System.Drawing.Image.FromFile(HttpContext.Current.Server.MapPath(SourceImagePath));		
			int num = ((ThumbnailImageWidth / 4) * 3);
			int width = image.Width;
			int height = image.Height;
			//计算图片的比例
			if ((((double) width) / ((double) height)) >= 1.3333333333333333f)
			{
				num = ((height * ThumbnailImageWidth) / width);
			}
			else
			{
				ThumbnailImageWidth = ((width * num) / height);
			}
			if ((ThumbnailImageWidth < 1) || (num < 1))
			{
				return;
			}
			//用指定的大小和格式初始化 Bitmap 类的新实例
			Bitmap bitmap = new Bitmap(ThumbnailImageWidth, num, PixelFormat.Format32bppArgb);
			//从指定的 Image 对象创建新 Graphics 对象
			Graphics graphics = Graphics.FromImage(bitmap);
			//清除整个绘图面并以透明背景色填充
			graphics.Clear(Color.Transparent);
			//在指定位置并且按指定大小绘制 原图片 对象
			graphics.DrawImage(image, new Rectangle(0, 0, ThumbnailImageWidth, num));
			image.Dispose();				
			try
			{			
				//将此 原图片 以指定格式并用指定的编解码参数保存到指定文件	
				string savepath = (ThumbnailImagePath==null?SourceImagePath:ThumbnailImagePath);		
				SaveImage(bitmap,HttpContext.Current.Server.MapPath(savepath),GetCodecInfo((string)htmimes[sExt]));
			}
			catch(System.Exception e)
			{
				throw e;
			}
			finally
			{
				bitmap.Dispose();						
				graphics.Dispose();
			}
		}
		#endregion

	}
}