如何从一个PdfFile使用iTextSharp的PdfReader的UserUnit财产 [英] How to get the UserUnit property from a PdfFile using iTextSharp PdfReader

问题描述

我有一大堆的PDF文件 - 我阅读这些按要求转化为字节数组，然后也把它传递给一个iTextSharp的PdfReader实例。我想，然后抢在像素，每个像素页面级的尺寸。从我目前看似乎通过PDF文件点 - 点是存储在名为UserUnit元素某种词典的配置单位工作。

I have a bunch of PDF files- I read these as requested into a byte array and then also pass it to a iTextSharp PdfReader instance. I want to then grab the dimensions of each page- in pixels. From what I've read so far it seems by PDF files work in points- a point being a configurable unit stored in some kind of dictionary in an element called UserUnit.

加载我的PDF文件转换成PdfReader，做什么，我需要做的就是在UserUnit每一页（显然它可以一页一页地而异），这样的话，我可以让页面尺寸以像素为单位。

Loading my PDF File into a PdfReader, what do I need to do to get the UserUnit for each page (apparently it can vary from page to page) so I can then get the page dimensions in pixels.

在present我有这个code，它抓住了尺寸为每个页面中的点 - 猜我只需要UerUnit，然后可以由乘这些尺寸得到像素或类似的东西。

At present I have this code, which grabs the dimensions for each page in "points" - guess I just need the UerUnit, and can then multiply these dimensions by that to get pixels or something similar.

//Create an object to read the PDF
PdfReader reader = new iTextSharp.text.pdf.PdfReader(file_content);

for (int i = 1; i <= reader.NumberOfPages; i++)
{
  Rectangle dim = reader.GetPageSize(i);
  int[] xy = new int[] { (int)dim.Width, (int)dim.Height };  // returns page size in "points"
  page_data[objectid + '-' + i] = xy;
}

干杯！

推荐答案

请允许我从我的书中引述如下：

Allow me to quote from my book:

iText的在行动 - 第二版，第9页：

iText in Action - Second Edition, page 9:

常见问题 什么是在PDF文档中的测量单位？的大多数测量   在PDF中的pssed在用户空间单位EX $ P $。 ISO-32000-1（第8.3.2.3）告诉我们   默认为单元在默认的用户空间的尺寸（72英寸）是   大致相同的点（角），一个单位被广泛应用于印刷   行业。它是不完全一样;有一点没有统一的定义。   总之，1〜=25.4毫米= 72用户单位（大致相当于72磅）。

FAQ What is the measurement unit in PDF documents? Most of the measurements in PDFs are expressed in user space units. ISO-32000-1 (section 8.3.2.3) tells us "the default for the size of the unit in default user space (1/72 inch) is approximately the same as a point (pt), a unit widely used in the printing industry. It is not exactly the same; there is no universal definition of a point." In short, 1 in. = 25.4 mm = 72 user units (which roughly corresponds to 72 pt).

在接下来的页面中，我解释说，这是可以改变用户单位的默认值，我加了如何创建具有不同的用户单元页的文档的例子。

On the next page, I explain that it’s possible to change the default value of the user unit, and I add an example on how to create a document with pages that have a different user unit.

现在你的问题：假设你有一个现有的PDF，你如何找到使用哪个用户单位？在我们回答这个问题，我们需要看看ISO-32000-1。

Now for your question: suppose you have an existing PDF, how do you find which user unit was used? Before we answer this, we need to take a look at ISO-32000-1.

在部分7.7.3.3Page对象，你会发现UserUnit在表30的描述，在一个页面参赛对象：

In section 7.7.3.3Page Objects, you'll find the description of UserUnit in Table 30, "Entries in a page object":

（可选; PDF 1.6）的正数给予的尺寸   缺省用户空间单位，在1/72英寸的倍数。的范围   支持的值应是实现相关的。默认值：1.0   （用户空间单位为1/72英寸）。

(Optional; PDF 1.6) A positive number that shall give the size of default user space units, in multiples of 1⁄72 inch. The range of supported values shall be implementation-dependent. Default value: 1.0 (user space unit is 1⁄72 inch).

此键被引入PDF 1.6;你不会发现它在旧文件。它是可选的，所以你不会总是发现它在每一页的字典。在我的书中，我也解释说，UserUnit关键的最大值为75,000

This key was introduced in PDF 1.6; you won't find it in older files. It's optional, so you won't always find it in every page dictionary. In my book, I also explain that the maximum value of the UserUnit key is 75,000.

现在如何检索此值与iTextSharp的？

您已经有矩形黯淡= reader.GetPageSize（我）; 返回媒体框。这可能不是页面的视觉部分的大小。如果有在页面中定义一个裁剪框，观众会表现出更小的尺寸比你所拥有的 XY （但你可能已经知道了）。

You already have Rectangle dim = reader.GetPageSize(i); which returns the MediaBox. This may not be the size of the visual part of the page. If there's a CropBox defined for the page, viewers will show a much smaller size than what you have in xy (but you probably knew that already).

您现在需要的是页字典，这样就可以检索UserUnit键的值：

What you need now is the page dictionary, so that you can retrieve the value of the UserUnit key:

PdfDictionary pageDict = reader.GetPageN(i);
PdfNumber userUnit = pageDict.GetAsNumber(PdfName.USERUNIT);

很多时候userUnit将空，但如果不是，您可以使用 userUnit.FloatValue

Most of the times userUnit will be null, but if it isn't you can use userUnit.FloatValue.

这篇关于如何从一个PdfFile使用iTextSharp的PdfReader的UserUnit财产的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！