从PDF中提取不可选择的内容

Question

我正在使用Apache PDFBox从PDF文件中提取页面，我找不到一种方法来提取不可选择的内容（文本或图像）。有了可从PDF文件中选择的内容，就没有问题了。

请注意，所讨论的PDF文件在复制内容方面没有任何限制，至少从我在文件的“文档限制摘要”中看到的是这样的：它们都允许“内容复制”和“内容复制以供访问”！在同一个PDF文件中，有可选择的内容，也有不可选择的其他部分。发生的情况是，提取的页面带有“漏洞”，即它们只有PDF的可选择部分。然而，在MS Word上，如果我将PDF作为对象添加，则会显示PDF页面的全部内容！因此，我希望对PDFBox lib或任何其他Javalib做同样的事情！

以下是我用来将PDF页面转换为图像的代码：

private void convertPdfToImage(File pdfFile, int pdfId) throws IOException {
   PDDocument document = PDDocument.loadNonSeq(pdfFile, null);
   List<PDPage> pdPages = document.getDocumentCatalog().getAllPages();
   for (PDPage pdPage : pdPages) { 
       BufferedImage bim = pdPage.convertToImage(BufferedImage.TYPE_INT_RGB, 300);
       ImageIOUtil.writeImage(bim, TEMP_FILEPATH + pdfId + ".png", 300);
   }
   document.close();
}

有没有办法用这个ApachePDFBox库（或其他类似库）从PDF中提取不可选择的内容？或者这根本不可能？如果事实并非如此，为什么？

非常感谢您的帮助！

编辑：我使用Adobe Reader作为PDF查看器和PDFBox v1。8.以下是PDF示例：https://dl.dropboxusercontent.com/u/2815529/test.pdf

Answer 1

这两幅图片，右上角的fischer徽标和稍微向下的小草图，都是通过在页面的某个区域填充平铺图案绘制的，而平铺图案在其内容流中依次绘制相应的图像。

Adobe Reader不允许选择模式的内容，自动图像提取器通常也不会遍历模式资源树。

您可以使用PDFBox相当轻松地构建图案图像提取器，例如，对于PDFBox 1.8.10：

public void extractPatternImages(PDDocument document, String fileNameFormat) throws IOException
{
    List<PDPage> pages = document.getDocumentCatalog().getAllPages();
    if (pages == null)
        return;

    for (int i = 0; i < pages.size(); i++)
    {
        String pageFormat = String.format(fileNameFormat, "-" + i + "%s", "%s");
        extractPatternImages(pages.get(i), pageFormat);
    }
}

public void extractPatternImages(PDPage page, String pageFormat) throws IOException
{
    PDResources resources = page.getResources();
    if (resources == null)
        return;
    Map<String, PDPatternResources> patterns = resources.getPatterns();

    for (Map.Entry<String, PDPatternResources> patternEntry : patterns.entrySet())
    {
        String patternFormat = String.format(pageFormat, "-" + patternEntry.getKey() + "%s", "%s");
        extractPatternImages(patternEntry.getValue(), patternFormat);
    }
}

public void extractPatternImages(PDPatternResources pattern, String patternFormat) throws IOException
{
    COSDictionary resourcesDict = (COSDictionary) pattern.getCOSDictionary().getDictionaryObject(COSName.RESOURCES);
    if (resourcesDict == null)
        return;
    PDResources resources = new PDResources(resourcesDict);
    Map<String, PDXObject> xObjects = resources.getXObjects();
    if (xObjects == null)
        return;

    for (Map.Entry<String, PDXObject> entry : xObjects.entrySet())
    {
        PDXObject xObject = entry.getValue();
        String xObjectFormat = String.format(patternFormat, "-" + entry.getKey() + "%s", "%s");
        if (xObject instanceof PDXObjectForm)
            extractPatternImages((PDXObjectForm)xObject, xObjectFormat);
        else if (xObject instanceof PDXObjectImage)
            extractPatternImages((PDXObjectImage)xObject, xObjectFormat);
    }
}

public void extractPatternImages(PDXObjectForm form, String imageFormat) throws IOException
{
    PDResources resources = form.getResources();
    if (resources == null)
        return;
    Map<String, PDXObject> xObjects = resources.getXObjects();
    if (xObjects == null)
        return;

    for (Map.Entry<String, PDXObject> entry : xObjects.entrySet())
    {
        PDXObject xObject = entry.getValue();
        String xObjectFormat = String.format(imageFormat, "-" + entry.getKey() + "%s", "%s");
        if (xObject instanceof PDXObjectForm)
            extractPatternImages((PDXObjectForm)xObject, xObjectFormat);
        else if (xObject instanceof PDXObjectImage)
            extractPatternImages((PDXObjectImage)xObject, xObjectFormat);
    }

    Map<String, PDPatternResources> patterns = resources.getPatterns();

    for (Map.Entry<String, PDPatternResources> patternEntry : patterns.entrySet())
    {
        String patternFormat = String.format(imageFormat, "-" + patternEntry.getKey() + "%s", "%s");
        extractPatternImages(patternEntry.getValue(), patternFormat);
    }
}

public void extractPatternImages(PDXObjectImage image, String imageFormat) throws IOException
{
    image.write2OutputStream(new FileOutputStream(String.format(imageFormat, "", image.getSuffix())));
}

（ExtractPatternImages.java）

我把它应用到你的样本PDF上，就像这样

public void testtestDrJorge() throws IOException
{
    try (InputStream resource = getClass().getResourceAsStream("testDrJorge.pdf"))
    {
        PDDocument document = PDDocument.load(resource);
        extractPatternImages(document, "testDrJorge%s.%s");;
    }
}

（ExtractPatternImages.java）

有两张照片：

>

testDrJorge-0-R38-R37。巴布亚新几内亚

这些图像失去了红色部分。这很可能是由于PDFBox版本1。x、 x不正确支持CMYK图像的提取，参见PDFBOX-2128（不正确支持CMYK图像），并且您的图像在CMYK中。

我将代码更新为PDFBox 2.0.0（目前仅作为候选版本提供）：

public void extractPatternImages(PDDocument document, String fileNameFormat) throws IOException
{
    PDPageTree pages = document.getDocumentCatalog().getPages();
    if (pages == null)
        return;

    for (int i = 0; i < pages.getCount(); i++)
    {
        String pageFormat = String.format(fileNameFormat, "-" + i + "%s", "%s");
        extractPatternImages(pages.get(i), pageFormat);
    }
}

public void extractPatternImages(PDPage page, String pageFormat) throws IOException
{
    PDResources resources = page.getResources();
    if (resources == null)
        return;
    Iterable<COSName> patternNames = resources.getPatternNames();

    for (COSName patternName : patternNames)
    {
        String patternFormat = String.format(pageFormat, "-" + patternName + "%s", "%s");
        extractPatternImages(resources.getPattern(patternName), patternFormat);
    }
}

public void extractPatternImages(PDAbstractPattern pattern, String patternFormat) throws IOException
{
    COSDictionary resourcesDict = (COSDictionary) pattern.getCOSObject().getDictionaryObject(COSName.RESOURCES);
    if (resourcesDict == null)
        return;
    PDResources resources = new PDResources(resourcesDict);
    Iterable<COSName> xObjectNames = resources.getXObjectNames();
    if (xObjectNames == null)
        return;

    for (COSName xObjectName : xObjectNames)
    {
        PDXObject xObject = resources.getXObject(xObjectName);
        String xObjectFormat = String.format(patternFormat, "-" + xObjectName + "%s", "%s");
        if (xObject instanceof PDFormXObject)
            extractPatternImages((PDFormXObject)xObject, xObjectFormat);
        else if (xObject instanceof PDImageXObject)
            extractPatternImages((PDImageXObject)xObject, xObjectFormat);
    }
}

public void extractPatternImages(PDFormXObject form, String imageFormat) throws IOException
{
    PDResources resources = form.getResources();
    if (resources == null)
        return;
    Iterable<COSName> xObjectNames = resources.getXObjectNames();
    if (xObjectNames == null)
        return;

    for (COSName xObjectName : xObjectNames)
    {
        PDXObject xObject = resources.getXObject(xObjectName);
        String xObjectFormat = String.format(imageFormat, "-" + xObjectName + "%s", "%s");
        if (xObject instanceof PDFormXObject)
            extractPatternImages((PDFormXObject)xObject, xObjectFormat);
        else if (xObject instanceof PDImageXObject)
            extractPatternImages((PDImageXObject)xObject, xObjectFormat);
    }

    Iterable<COSName> patternNames = resources.getPatternNames();

    for (COSName patternName : patternNames)
    {
        String patternFormat = String.format(imageFormat, "-" + patternName + "%s", "%s");
        extractPatternImages(resources.getPattern(patternName), patternFormat);
    }
}

public void extractPatternImages(PDImageXObject image, String imageFormat) throws IOException
{
    String filename = String.format(imageFormat, "", image.getSuffix());
    ImageIOUtil.writeImage(image.getOpaqueImage(), "png", new FileOutputStream(filename));
}

得到

>

testDrJorge-0-COSName{R15}-COSName{R14}。巴布亚新几内亚

testDrJorge-0-COSName{R38}-COSName{R37}. png

看起来像一个改进...；）