使用iText为标记为pdf（PDF / UA）的图像添加替代文本 [英] Add alternative text for an image in tagged pdf (PDF/UA) using iText

问题描述

我在

代码无法识别狐狸或狗，因此我们使用Alt属性创建一个新文档，说没有Alt描述的图：

我们通过遍历结构树来添加此描述，查找标记为 / Figure 元素的结构元素：

  public void manipulatePdf（String src，String dest）
抛出IOException，DocumentException {
 PdfReader reader = new PdfReader（src）; 
 PdfDictionary catalog = reader.getCatalog（）; 
 PdfDictionary structTreeRoot = 
 catalog.getAsDict（PdfName.STRUCTTREEROOT）; 
操纵（structTreeRoot）; 
 PdfStamper压模=新的PdfStamper（
 reader，new FileOutputStream（dest））; 
 stamper.close（）; 
} 
 
 public void manipulate（PdfDictionary element）{
 if（element == null）
 return; 
 if（PdfName.FIGURE.equals（element.get（PdfName.S）））{
 element.put（PdfName.ALT，
 new PdfString（没有Alt描述的图）） ）; 
} 
 PdfArray kids = element.getAsArray（PdfName.K）; 
如果（kids == null）返回; 
 for（int i = 0; i< kids.size（）; i ++）
 manipulate（kids.getAsDict（i））; 
} 
  

您可以轻松地将此Java示例移植到C＃：

• 从 PdfReader 对象中获取根词典，


• 获取结构树的根（字典），


• 遍历该树的每个分支的所有孩子，


• 当一个领导是一个如图所示，添加 / Alt 条目。

完成后，使用 PdfStamper 保存更改的文件。

I've looked up some documentations and examples under the http://developers.itextpdf.com/examples.

I know iText is able to generate tagged pdf from scratch, but is it possible to insert alternative text to images in an existing tagged pdf (without changing anything else)? I need to implement this feature in a program without using GUI applications (such as Adobe Acrobat Pro). Thanks.

解决方案

Please take a look at the AddAltTags example.

In this example, we take a PDF with images of a fox and a dog where the Alt keys are missing: no_alt_attribute.pdf

Code can't recognize a fox or a dog, so we create a new document with Alt attributes saying "Figure without an Alt description": added_alt_attributes.pdf)

We add this description by walking through the structure tree, looking for structural elements marked as /Figure elements:

public void manipulatePdf(String src, String dest)
    throws IOException, DocumentException {
    PdfReader reader = new PdfReader(src);
    PdfDictionary catalog = reader.getCatalog();
    PdfDictionary structTreeRoot =
        catalog.getAsDict(PdfName.STRUCTTREEROOT);
    manipulate(structTreeRoot);
    PdfStamper stamper = new PdfStamper(
        reader, new FileOutputStream(dest));
    stamper.close();
}

public void manipulate(PdfDictionary element) {
    if (element == null)
        return;
    if (PdfName.FIGURE.equals(element.get(PdfName.S))) {
        element.put(PdfName.ALT,
            new PdfString("Figure without an Alt description"));
    }
    PdfArray kids = element.getAsArray(PdfName.K);
    if (kids == null) return;
    for (int i = 0; i < kids.size(); i++)
        manipulate(kids.getAsDict(i));
}

You can easily port this Java example to C#:

• Get the root dictionary from the PdfReader object,
• Get the root of the structure tree (a dictionary),
• Loop over all the kids of every branch of that tree,
• When a lead is a figure, add an /Alt entry.

Once this is done, use PdfStamper to save the altered file.

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