asp.net的gdi+绘图

本来用asp.net gdi+绘制一个图片，生产的是jpg格式的，可是清晰度不够高。 但是在这里换成png的却报错 System.Drawing.Imaging.ImageCodecInfo ici = GetEncoderInfo("image/jpeg");
找了一堆资料，终于找到了，下面是代码！

 1using System;
 2using System.Data;
 3using System.Configuration;
 4using System.Collections;
 5using System.Web;
 6using System.Web.Security;
 7using System.Web.UI;
 8using System.Web.UI.WebControls;
 9using System.Web.UI.WebControls.WebParts;
10using System.Web.UI.HtmlControls;
11using System.Drawing;
12using System.Drawing.Drawing2D;
13using System.Drawing.Imaging;
14
15public partial class CreateImg : System.Web.UI.Page
16{
17    protected void Page_Load(object sender, EventArgs e)
18    {
19
20
21
22
23    }
24    private static ImageCodecInfo GetEncoderInfo(String mimeType)
25    {
26        ImageCodecInfo[] encoders;
27        encoders = ImageCodecInfo.GetImageEncoders();
28        for (int j = 0; j < encoders.Length; ++j)
29        {
30            if (encoders[j].MimeType == mimeType)
31                return encoders[j];
32        }
33        return null;
34    }
35    private Bitmap GetneralCodeImage()
36    {
37
38        //创建位图
39
40        Bitmap bmp = new Bitmap(150, 18);
41
42        Graphics g = Graphics.FromImage(bmp);
43        g.Clear(Color.FromArgb(247, 213, 225));
44        //描绘字符
45        g.DrawString("1366666666", new Font("Verdana", 11, FontStyle.Bold),
46                new SolidBrush(Color.FromArgb(255, 102, 0)),
47                0,
48                0
49            );
50        g.CompositingQuality = CompositingQuality.HighQuality;
51        g.SmoothingMode = SmoothingMode.HighQuality;
52        g.InterpolationMode = InterpolationMode.HighQualityBicubic;
53        g.PixelOffsetMode = PixelOffsetMode.HighQuality;
54        g.Dispose();
55        return bmp;
56    }
57
58    protected void btnpng_Click(object sender, EventArgs e)
59    {
60        //生成png图片(清晰度高)
61        System.IO.MemoryStream ms = new System.IO.MemoryStream();
62        GetneralCodeImage().Save(ms, ImageFormat.Png);
63        ms.WriteTo(Response.OutputStream);
64    }
65    protected void btnjpeg_Click(object sender, EventArgs e)
66    {
67        //生成jpg图片(清晰度不够)
68        System.Drawing.Imaging.EncoderParameters ep = new System.Drawing.Imaging.EncoderParameters(1);
69        ep.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 95L);
70        System.Drawing.Imaging.ImageCodecInfo ici = GetEncoderInfo("image/jpeg");//这里换成gif后文字显示可以,但背景不清楚
71        this.GetneralCodeImage().Save(Response.OutputStream, ici, ep);
72    }
73}
74