c#生成缩略图

来源：互联网发布：gpa 算法编辑：程序博客网时间：2024/04/27 18:17

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。

转自：http://blog.csdn.net/ojekleen/archive/2008/08/01/2754255.aspx

===========================

/// <summary>
        /// A better alternative to Image.GetThumbnail. Higher quality but slightly slower
        /// </summary>
        /// <param name="source"></param>
        /// <param name="thumbWi"></param>
        /// <param name="thumbHi"></param>
        /// <returns></returns>
        private static Bitmap CreateThumbnail(Bitmap source, int thumbWi, int thumbHi, bool maintainAspect)
        {
            // return the source image if it's smaller than the designated thumbnail
            if (source.Width < thumbWi && source.Height < thumbHi) return source;

            System.Drawing.Bitmap ret = null;
            try
            {
                int wi, hi;

                wi = thumbWi;
                hi = thumbHi;

                if (maintainAspect)
                {
                    // maintain the aspect ratio despite the thumbnail size parameters
                    if (source.Width > source.Height)
                    {
                        wi = thumbWi;
                        hi = (int)(source.Height * ((decimal)thumbWi / source.Width));
                    }
                    else
                    {
                        hi = thumbHi;
                        wi = (int)(source.Width * ((decimal)thumbHi / source.Height));
                    }
                }

                // original code that creates lousy thumbnails
                // System.Drawing.Image ret = source.GetThumbnailImage(wi,hi,null,IntPtr.Zero);
                ret = new Bitmap(wi, hi);
                using (Graphics g = Graphics.FromImage(ret))
                {
                    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    g.FillRectangle(Brushes.White, 0, 0, wi, hi);
                    g.DrawImage(source, 0, 0, wi, hi);
                    g.Dispose();
                }
            }
            catch
            {
                ret = null;
            }
            return ret;
        }
        public static void CreateCompressThumbnail(Bitmap source, int thumbWi, int thumbHi, bool maintainAspect, string SavePathThumb, string fileName)
        {
            using (System.Drawing.Image myThumbnail = CreateThumbnail(source, thumbWi, thumbHi, maintainAspect))
            {
                System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
                long[] quality = new long[1];
                quality[0] = 75;
                System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
                encoderParams.Param[0] = encoderParam;

                System.Drawing.Imaging.ImageCodecInfo[] arrayICI = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
                System.Drawing.Imaging.ImageCodecInfo jpegICI = null;
                for (int x = 0; x < arrayICI.Length; x++)
                {
                    if (arrayICI[x].FormatDescription.Equals("JPEG"))
                    {
                        jpegICI = arrayICI[x];
                        break;
                    }
                }
                myThumbnail.Save(Path.Combine(SavePathThumb, fileName + ".jpg"), jpegICI, encoderParams);
                myThumbnail.Dispose();
            }
        }
==========