关于图片缩放的c#方法

Posted 2020-08-22

  在网站建设中，关于图片是必不可少的，后台管理中往往需要上传图片，大的图片在网络中传输速率很慢，很不理想，因此解决办法是，用户上传图片时候，保存一个图片的缩略图，在网页显示用缩略图，用户下载，使用原图，下面是通过搜索资料，整理的c#关于保存图片缩略图的方法，用户只需要传入适当参数，调用此方法就可以生成缩略图。

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Web;
    using System.Web.UI;
    using System.Web.UI.WebControls;
    using System.IO;   
    public partial class upload : System.Web.UI.Page 
    {     
        protected void Page_Load(object sender, EventArgs e)     
        {         
                 
        }     
    }  
    /// <summary>     
    /// 图片等比缩放     
    /// </summary>     
    /// <param name="postedfile">原图地址加名称</param>     
    /// <param name="savepath">缩略图存放地址</param>     
    /// <param name="smallname">缩略图名称</param>     
    /// <param name="targetwidth">指定的最大宽度</param>     
    /// <param name="targetheight">指定的最大高度</param>     
    public static void zoomauto(string initpath, string savepath,string smallname, double targetwidth, double targetheight)     
    {         
        //虚拟路径转绝对路径         
        initpath = System.Web.HttpContext.Current.Server.MapPath(initpath);         
        savepath = System.Web.HttpContext.Current.Server.MapPath(savepath);         
        //创建目录         
        string dir = Path.GetDirectoryName(savepath);         
        if (!Directory.Exists(dir))             
            Directory.CreateDirectory(dir);  
        
        //原始图片（获取原始图片创建对象，并使用流中嵌入的颜色管理信息）         
        System.Drawing.Image initimage = System.Drawing.Image.FromFile(initpath);  
        //原图宽高均小于模版，不作处理，直接保存         
        if (initimage.Width <= targetwidth && initimage.Height <= targetheight)         
        {             
            //保存             
            initimage.Save(savepath + smallname, System.Drawing.Imaging.ImageFormat.Jpeg);         
        }         
        else         
        {             
            //缩略图宽、高计算             
            double newwidth = initimage.Width;             
            double newheight = initimage.Height;  
            //宽大于高或宽等于高（横图或正方）             
            if (initimage.Width > initimage.Height || initimage.Width == initimage.Height)             
            {                 
                //如果宽大于模版                 
                if (initimage.Width > targetwidth) 
                {                     
                    //宽按模版，高按比例缩放                     
                    newwidth = targetwidth;                     
                    newheight = initimage.Height * (targetwidth / initimage.Width);                 
                }             
            }             
            //高大于宽（竖图）             
            else             
            {                 
                //如果高大于模版                 
                if (initimage.Height > targetheight)                 
                {                     
                    //高按模版，宽按比例缩放                     
                    newheight = targetheight;                     
                    newwidth = initimage.Width * (targetheight / initimage.Height);                 
                }             
            }  
            
            //生成新图             
            //新建一个bmp图片             
            System.Drawing.Image newimage = new System.Drawing.Bitmap((int)newwidth, (int)newheight);             
            //新建一个画板             
            System.Drawing.Graphics newg = System.Drawing.Graphics.FromImage(newimage);  
            //设置质量             
            newg.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;             
            newg.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;  
            //置背景色             
            newg.Clear(System.Drawing.Color.White);             
            //画图             
            newg.DrawImage(initimage, new System.Drawing.Rectangle(0, 0, newimage.Width, newimage.Height), new System.Drawing.Rectangle(0, 0, initimage.Width, initimage.Height), System.Drawing.GraphicsUnit.Pixel);  
            //保存缩略图             
            newimage.Save(savepath + smallname, System.Drawing.Imaging.ImageFormat.Jpeg);  
            //释放资源             
            newg.Dispose();             
            newimage.Dispose();             
            initimage.Dispose(); 
        
        }     
    }  
}

本文出自 “梦里开花，梦里飞” 博客，请务必保留此出处http://wppeng.blog.51cto.com/9894483/1881627