对于GDI+,在正常的操作,Bitmap-- Graphcis -- DrawImage或者DrawString ,生成图片的话,会产生很多杂点,或者是图片质量不稳定..尤其是在读取图片后,生成缩略图之后,文件会被压缩而失真..

主要原因是因为没有重新设置Graphics的几个属性..

1.Graphics.SmoothingMode属性: 例如SmoothingMode.HighQuality可以产生高质量图片,但是效率低.

2.Graphics.CompositingQuality 属性: 例如:CompositingQuality.HighQuality也是产生高质量图,效率低下.

3.Graphics.InterpolationMode 属性,例如:InterpolationMode.HighQualityBicubic与前两个也是同样的效果.

这三个属性的值都是enum,具体的enum参数可以查看MSDN的说明..在这里就我不赘述..
如果是对图片进行放大,缩小,可以调整Graphics.CompositingQuality 和Graphics.InterpolationMode 两个属性..如果是图片生成,则可以调整Graphics.SmoothingMode属性..

另外一个问题就是关于文字生成的..按照正常的模式生成的文字,可以很明显的看到文字带有锯齿..解决的办法也是需要修改Graphics的一个属性: Graphics.TextRenderingHint...注意一点,修改TextRenderingHint的话,需要引入System.Drawing.Text,例如:Graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;

 经过对这四个属性的修改,操作大部分的图片之后,产生的结果都是比较让人满意的..

在这里提供一个简单的例子..是生成印章签名的效果..提供四种字体选择..并产生一个图片..如果你的机器中没有安装指定的几种字体,你需要把字体修改一下...直接把代码拷贝..就可以看到效果...

ASPX页面:
 

 1 <% @ Page language = " c# "  Codebehind = " underWrite.aspx.cs "  AutoEventWireup = " false "  Inherits = " testItem.movie.underWrite "   %>
 2 <! DOCTYPE HTML PUBLIC  " -//W3C//DTD HTML 4.0 Transitional//EN "   >
 3 < HTML >
 4      < HEAD >
 5          < title > underWrite </ title >
 6          < meta name = " GENERATOR "  Content = " Microsoft Visual Studio .NET 7.1 " >
 7          < meta name = " CODE_LANGUAGE "  Content = " C# " >
 8          < meta name = " vs_defaultClientScript "  content = " JavaScript " >
 9          < meta name = " vs_targetSchema "  content = " http://schemas.microsoft.com/intellisense/ie5 " >
10      </ HEAD >
11      < body MS_POSITIONING = " GridLayout " >
12          < form id = " Form1 "  method = " post "  runat = " server " >
13              < asp:Image id = " Image1 "  style = " Z-INDEX: 101; LEFT: 208px; POSITION: absolute; TOP: 360px "  runat = " server " ></ asp:Image >
14              < asp:HyperLink id = " HyperLink1 "  style = " Z-INDEX: 105; LEFT: 304px; POSITION: absolute; TOP: 312px "
15                 runat = " server "  NavigateUrl = " ../mv/index.html " > 大头帖 </ asp:HyperLink >
16              < asp:TextBox id = " name "  style = " Z-INDEX: 104; LEFT: 208px; POSITION: absolute; TOP: 144px "  runat = " server "
17                 MaxLength = " 4 " ></ asp:TextBox >
18              < asp:RadioButtonList id = " fontType "  style = " Z-INDEX: 103; LEFT: 208px; POSITION: absolute; TOP: 184px "
19                 runat = " server "  Width = " 240px " >
20                  < asp:ListItem Value = " 方正黄草简体 "  Selected = " True " > 方正黄草简体 </ asp:ListItem >
21                  < asp:ListItem Value = " 汉鼎繁淡古 " > 汉鼎繁淡古 </ asp:ListItem >
22                  < asp:ListItem Value = " 汉鼎繁印篆 " > 汉鼎繁印篆 </ asp:ListItem >
23                  < asp:ListItem Value = " 经典繁桟亭 " > 经典繁桟亭 </ asp:ListItem >
24              </ asp:RadioButtonList >
25              < asp:Button id = " bu "  style = " Z-INDEX: 102; LEFT: 208px; POSITION: absolute; TOP: 312px "  runat = " server "
26                 Text = "  刻 字  " ></ asp:Button >
27          </ form >
28      </ body >
29 </ HTML >
30

  1 using  System;
  2 using  System.Collections;
  3 using  System.ComponentModel;
  4 using  System.Data;
  5 using  System.Drawing;
  6 using  System.Drawing.Drawing2D;
  7 using  System.IO;
  8 using  System.Web;
  9 using  System.Web.SessionState;
 10 using  System.Web.UI;
 11 using  System.Web.UI.WebControls;
 12 using  System.Web.UI.HtmlControls;
 13
 14 namespace  testItem.movie
 15 {
 16    /**//// <summary>
 17    ///        生成印章签名
 18    /// </summary>
 19    public class underWrite : System.Web.UI.Page
 20    {
 21        protected System.Web.UI.WebControls.Image Image1;
 22        protected System.Web.UI.WebControls.RadioButtonList fontType;
 23        protected System.Web.UI.WebControls.HyperLink HyperLink1;
 24        protected System.Web.UI.WebControls.Button bu;
 25        protected System.Web.UI.WebControls.TextBox name;
 26        
 27        private void Page_Load(object sender, System.EventArgs e) 
 28        {
 29            Image1.Visible = false;
 30        }
 31
 32        Web 窗体设计器生成的代码#region Web 窗体设计器生成的代码
 33        override protected void OnInit(EventArgs e)
 34        {
 35            //
 36            // CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
 37            //
 38            InitializeComponent();
 39            base.OnInit(e);
 40        }
 41        
 42        /**//// <summary>
 43        /// 设计器支持所需的方法 - 不要使用代码编辑器修改
 44        /// 此方法的内容。
 45        /// </summary>
 46        private void InitializeComponent()
 47        {    
 48            this.bu.Click += new System.EventHandler(this.Button1_Click);
 49            this.Load += new System.EventHandler(this.Page_Load);
 50
 51        }
 52        #endregion
 53
 54        private void Button1_Click(object sender, System.EventArgs e)
 55        {
 56            string Name = name.Text;
 57            if ( Name.Length < 4 ) {
 58                Response.Write( "请输入最少4个字符!" );
 59                return;
 60            }
 61            
 62            string FontName = fontType.SelectedValue;
 63            
 64            int fontSize = 36;
 65            int x = 10;
 66            int y = 10;
 67            
 68            switch( FontName ) {
 69                case "方正黄草简体":
 70                    x = -8;
 71                    y = -2;
 72                    fontSize = 42;
 73                    break;
 74                    
 75                case "汉鼎繁淡古":
 76                    x = -10;
 77                    y = -2;
 78                    break;
 79                
 80                case "汉鼎繁印篆":
 81                    x = -15;
 82                    y = -2;
 83                    break;
 84                
 85                case "经典繁桟亭":
 86                    fontSize = 34;
 87                    x = -10;
 88                    y = -3;
 89                    break;                    
 90            }
 91            
 92            Bitmap bm = new Bitmap(110,100,System.Drawing.Imaging.PixelFormat.Format32bppArgb);
 93            Font font = new Font(FontName,fontSize,FontStyle.Bold);
 94            
 95            Graphics g = Graphics.FromImage( bm );
 96            
 97            g.TextRenderingHint =  System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
 98            
 99            /**//*    这里的三个属性可以根据情况开放.
100             * 
101            //g.CompositingQuality = CompositingQuality.HighQuality; 
102            //g.SmoothingMode = SmoothingMode.HighQuality; 
103            //g.InterpolationMode = InterpolationMode.HighQualityBicubic; 
104            
105            */
106            g.Clear(Color.Red);        //赋予图像一个背景色
107            
108            g.DrawString( Name.Substring(2,1),font,new SolidBrush(Color.White),0,2 );
109            g.DrawString( Name.Substring(3,1),font,new SolidBrush(Color.White),0,45-y );
110            g.DrawString( Name.Substring(0,1),font,new SolidBrush(Color.White),35-x,2 );
111            g.DrawString( Name.Substring(1,1),font,new SolidBrush(Color.White),35-x,45-y );
112            g.Dispose();
113            //设置保存路径
114            bm.Save( Server.MapPath("../upload/c.jpg"),System.Drawing.Imaging.ImageFormat.Jpeg );
115            bm.Dispose();
116            //显示产生的图片
117            Image1.ImageUrl = Server.MapPath("../upload/c.jpg") ;
118            Image1.Visible = true;
119        }
120    }
121}
122