itextsharp图片生成pdf模糊问题解释

I forget to mention that I' am using itextsharp 5.0.2.

It turned out that PDF DPI = 110, which means 110 pixels per inch, and since itextsharp uses points as measurment unit then :

• n pixels = n/110 inches.
• n inches = n * 72 points.

Having a helper method to convert pixels to points is all I needed:

public static float PixelsToPoints(float value,int dpi)
{
   return value / dpi * 72;
}

By using the above formula and passing a dpi value of 110 it worked perfectly:

alt text http://www.freeimagehosting.net/uploads/1c8287b8d9.png

Note: Since you can create pdf documents in any size you want, this may lead to incorrect scaling when printing out your documents. To overcome this issue all you need to do is to have the correct aspect ratio between width and height [approximately 1:1.4142] (see : Paper Size - The international standard: ISO 216 ).

举个例子，有图片653*1636大小，生成PDF：所使用的尺寸应为，653/110 * 72 = 427.4,  1636/110 * 72 = 1070.8

iTextSharp.text.Rectangle Rec = new iTextSharp.text.Rectangle(427.5f, 1070.8f);
            //设置页面颜色
            //Rec.BackgroundColor = new iTextSharp.text.BaseColor(0, 0, 0);

            Document doc = new Document(Rec, 0, 0, 0, 0);

            try
            {
                PdfWriter writer = PdfWriter.GetInstance(doc,
                    new FileStream(@"C:Us***Images.pdf", FileMode.Create));
                doc.Open();
                doc.AddTitle("****相关电子资料");//标题
                doc.AddSubject("申请审批文档");//主题
                doc.AddKeywords("***表");//关键字
                doc.AddAuthor("**软件");//作者
                doc.AddCreationDate();//创建时间
                doc.AddCreator("***管理系统");
                writer.Info.Put(new PdfName("Producer"), new PdfString("江苏省**科技有限责任公司"));
                Paragraph para = new Paragraph();
                //para.IndentationLeft = 0f; //左缩进
                doc.Add(para);
                //foreach (string file in listBox1.Items)
                {
                    doc.NewPage();
                    iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(@"G:***Snap11.jpg");
                    //img.ScalePercent(100f);
                    img.ScaleAbsolute(Rec);
                    //img.SetDpi(200, 200);
                    //img.ScalePercent(72.0F / 96.0F * 100);

                    img.Alignment = iTextSharp.text.Image.UNDERLYING;
                    img.SetAbsolutePosition(0, 0);
                    doc.Add(img);
                }
            }
            catch (DocumentException dex)
            {
                MessageBox.Show(dex.Message);
            }
            catch (IOException ioex)
            {
                MessageBox.Show(ioex.Message);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                doc.Close();
            }