Asp.Net 上传图片并生成高清晰缩略图

晨曦之光 发布于 2012/05/16 17:14
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在asp.net中,上传图片功能或者是常用的,生成缩略图也是常用的。baidu或者google,c#的方法也是很多的,但是一用却发现缩略图不清晰啊,缩略图片太大之类的事情,下面是我在处理图片上的代码,效果不错,所以拿出来分享,(效果能达到一些绘图软件的效果)

代码如下:

 /// <summary>
    /// asp.net上传图片并生成缩略图
    /// </summary>
    /// <param name="upImage">HtmlInputFile控件</param>
    /// <param name="sSavePath">保存的路径,些为相对服务器路径的下的文件夹</param>
    /// <param name="sThumbExtension">缩略图的thumb</param>
    /// <param name="intThumbWidth">生成缩略图的宽度</param>
    /// <param name="intThumbHeight">生成缩略图的高度</param>
    /// <returns>缩略图名称</returns>
    public string UpLoadImage(HtmlInputFile upImage, string sSavePath, string sThumbExtension, int intThumbWidth, int intThumbHeight)
    {
        string sThumbFile = "";
        string sFilename = "";        

        if (upImage.PostedFile != null)
        {
            HttpPostedFile myFile = upImage.PostedFile;
            int nFileLen = myFile.ContentLength;
            if (nFileLen == 0)
                return "没有选择上传图片";            

            //获取upImage选择文件的扩展名
            string extendName = System.IO.Path.GetExtension(myFile.FileName).ToLower();
            //判断是否为图片格式
            if (extendName != ".jpg" && extendName != ".jpge" && extendName != ".gif" && extendName != ".bmp" && extendName != ".png")
                return "图片格式不正确";
            

            byte[] myData = new Byte[nFileLen];
            myFile.InputStream.Read(myData, 0, nFileLen);

            sFilename = System.IO.Path.GetFileName(myFile.FileName);
            int file_append = 0;
            //检查当前文件夹下是否有同名图片,有则在文件名+1
            while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename)))
            {
                file_append++;
                sFilename = System.IO.Path.GetFileNameWithoutExtension(myFile.FileName)
                    + file_append.ToString() + extendName;
            }
            System.IO.FileStream newFile
                = new System.IO.FileStream(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename),
                System.IO.FileMode.Create, System.IO.FileAccess.Write);
            newFile.Write(myData, 0, myData.Length);
            newFile.Close();

            //以上为上传原图

            try
            {
                //原图加载
                using (System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename)))
                {
                    //原图宽度和高度
                    int width = sourceImage.Width;
                    int height = sourceImage.Height;
                    int smallWidth;
                    int smallHeight;

                    //获取第一张绘制图的大小,(比较 原图的宽/缩略图的宽  和 原图的高/缩略图的高)
                    if (((decimal)width) / height <= ((decimal)intThumbWidth) / intThumbHeight)
                    {
                        smallWidth = intThumbWidth;
                        smallHeight = intThumbWidth * height / width;
                    }
                    else
                    {
                        smallWidth = intThumbHeight * width / height;
                        smallHeight = intThumbHeight;
                    }

                    //判断缩略图在当前文件夹下是否同名称文件存在
                    file_append = 0;
                    sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) + extendName;

                    while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sThumbFile)))
                    {
                        file_append++;
                        sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) +
                            file_append.ToString() + extendName;
                    }
                    //缩略图保存的绝对路径
                    string smallImagePath = System.Web.HttpContext.Current.Server.MapPath(sSavePath) + sThumbFile;

                    //新建一个图板,以最小等比例压缩大小绘制原图
                    using (System.Drawing.Image bitmap = new System.Drawing.Bitmap(smallWidth, smallHeight))
                    {
                        //绘制中间图
                        using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap))
                        {
                            //高清,平滑
                            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                            g.Clear(Color.Black);
                            g.DrawImage(
                            sourceImage,
                            new System.Drawing.Rectangle(0, 0, smallWidth, smallHeight),
                            new System.Drawing.Rectangle(0, 0, width, height),
                            System.Drawing.GraphicsUnit.Pixel
                            );
                        }
                        //新建一个图板,以缩略图大小绘制中间图
                        using (System.Drawing.Image bitmap1 = new System.Drawing.Bitmap(intThumbWidth, intThumbHeight))
                        {
                            //绘制缩略图
                            using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap1))
                            {
                                //高清,平滑
                                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                                g.Clear(Color.Black);
                                int lwidth = (smallWidth - intThumbWidth) / 2;
                                int bheight = (smallHeight - intThumbHeight) / 2;
                                g.DrawImage(bitmap, new Rectangle(0, 0, intThumbWidth, intThumbHeight), lwidth, bheight, intThumbWidth, intThumbHeight, GraphicsUnit.Pixel);
                                g.Dispose();
                                bitmap1.Save(smallImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);
                            }
                        }
                    }
                }
            }
            catch
            {
                //出错则删除
                System.IO.File.Delete(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename));
                return "图片格式不正确";
            }
            //返回缩略图名称
            return sThumbFile;
        }
        return "没有选择图片";
    }
HtmlInputFile控件我想大家都应该知道的,就是input type=file....

 

下面把调用代码也一起C上来

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>无标题页</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>        
        <input id="File1" runat="server" type="file" /></div><asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
    </form>
</body>
</html>

 

   protected void Button1_Click(object sender, EventArgs e)
    {
        string a = this.UpLoadImage(this.File1, "UpLoad/", "thumb_", 118, 118);  
    }
 

 

这样就会在你的UpLoad文件夹下多出两张图片,一张是原图,一张是缩略图。

 

 

提供一个更好的算法,由于没有时间去测试和调试,仅供参考

即,在第一步等比例缩小的时候,可以分多次,即把原图到上面代码的中间图以百分比缩小,

例如:原图为500*500 我要缩略成100*80,上面代码程序会先绘制一张100*100的中间图,再在这图片上绘制100*80的,

在绘制100*100中间图之前如果先绘300*300的中间图,再在300*300的基础上再绘100*100然后再绘100*80这样会比我上面的代码效果更好,图片更清晰,即中间图越多,效果越好,大家可以去试试。


原文链接:http://blog.csdn.net/maji9370/article/details/6162758
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