java - 即使没有与 PDFBox 中的布局相关的属性(文档目录结构中的/A)，也获取标签的相关 BBox？

Question

当他们选择结构根中的标签时，我想突出显示特定标签的 bbox。因此，当标签包含这样的属性时，我能够获取 bbox

.

但我发现在一些 pdf 文件中，即使没有 (/A) 这样的属性，当您选择特定标签时，Adobe dc 也可以突出显示内容(bbox 的)。在这种情况下我怎样才能得到bbox？我尝试获取与 bbox 相关的属性的代码是

String inputPdfFile = "D:/Documents/pdfs/res.pdf";
PDDocument old_document = PDDocument.load(new File(inputPdfFile));
PDStructureTreeRoot treeRoot = old_document.getDocumentCatalog().getStructureTreeRoot();
for (Object kid : treeRoot.getKids()){
    for (Object kid2 :((PDStructureElement)kid).getKids()){
        PDStructureElement kid2c = (PDStructureElement)kid2;
        for (Object kid3 : kid2c.getKids()){
            if (kid3 instanceof PDStructureElement){
                PDStructureElement kid3c = (PDStructureElement)kid3;
                System.out.println(kid3c.getAttributes());
            }
        }
    }
}

pdf 链接是 https://drive.google.com/file/d/1_-tuWuReaTvrDsqQwldTnPYrMHSpXIWp/view?usp=sharing

请帮助我......

Answer 1

要确定某些标记内容的文本的实际边界框(与某些结构元素布局属性中给出的边界框相反)，您可以使用 PDFBox PDFMarkedContentExtractor 并将其结果与PDF 结构树数据。

以下代码执行此操作并创建一个输出 PDF，其中确定的边界框包含在彩色矩形中:

PDDocument document = PDDocument.load(SOURCE);

Map<PDPage, Map<Integer, PDMarkedContent>> markedContents = new HashMap<>();

for (PDPage page : document.getPages()) {
    PDFMarkedContentExtractor extractor = new PDFMarkedContentExtractor();
    extractor.processPage(page);

    Map<Integer, PDMarkedContent> theseMarkedContents = new HashMap<>();
    markedContents.put(page, theseMarkedContents);
    for (PDMarkedContent markedContent : extractor.getMarkedContents()) {
        addToMap(theseMarkedContents, markedContent);
    }
}

PDStructureNode root = document.getDocumentCatalog().getStructureTreeRoot();
Map<PDPage, PDPageContentStream> visualizations = new HashMap<>();
showStructure(document, root, markedContents, visualizations);
for (PDPageContentStream canvas : visualizations.values())
    canvas.close();

document.save(RESULT);

(来自 VisualizeMarkedContent 方法可视化)

它使用以下辅助方法通过 MCID 递归映射 PDMarkedContent 对象:

void addToMap(Map<Integer, PDMarkedContent> theseMarkedContents, PDMarkedContent markedContent) {
    theseMarkedContents.put(markedContent.getMCID(), markedContent);
    for (Object object : markedContent.getContents()) {
        if (object instanceof PDMarkedContent) {
            addToMap(theseMarkedContents, (PDMarkedContent)object);
        }
    }
}

(VisualizeMarkedContent辅助方法)

方法showStructure递归地确定结构元素的边界框，并为每个元素分别绘制一个矩形。实际上，结构元素可以包含跨页面的内容，因此我们必须在其 boxes 变量中处理页面到边界框的映射...

Map<PDPage, Rectangle2D> showStructure(PDDocument document, PDStructureNode node, Map<PDPage, Map<Integer, PDMarkedContent>> markedContents, Map<PDPage, PDPageContentStream> visualizations) throws IOException {
    Map<PDPage, Rectangle2D> boxes = null;
    PDPage page = null;
    if (node instanceof PDStructureElement) {
        PDStructureElement element = (PDStructureElement) node;
        page = element.getPage();
    }
    Map<Integer, PDMarkedContent> theseMarkedContents = markedContents.get(page);
    for (Object object : node.getKids()) {
        if (object instanceof COSArray) {
            for (COSBase base : (COSArray) object) {
                if (base instanceof COSDictionary) {
                    boxes = union(boxes, showStructure(document, PDStructureNode.create((COSDictionary) base), markedContents, visualizations));
                } else if (base instanceof COSNumber) {
                    boxes = union(boxes, page, showContent(((COSNumber)base).intValue(), theseMarkedContents));
                } else {
                    System.out.printf("?%s\n", base);
                }
            }
        } else if (object instanceof PDStructureNode) {
            boxes = union(boxes, showStructure(document, (PDStructureNode) object, markedContents, visualizations));
        } else if (object instanceof Integer) {
            boxes = union(boxes, page, showContent((Integer)object, theseMarkedContents));
        } else {
            System.out.printf("?%s\n", object);
        }

    }
    if (boxes != null) {
        Color color = new Color((int)(Math.random() * 256), (int)(Math.random() * 256), (int)(Math.random() * 256));

        for (Map.Entry<PDPage, Rectangle2D> entry : boxes.entrySet()) {
            page = entry.getKey();
            Rectangle2D box = entry.getValue();
            if (box == null)
                continue;

            PDPageContentStream canvas = visualizations.get(page);
            if (canvas == null) {
                canvas = new PDPageContentStream(document, page, AppendMode.APPEND, false, true);
                visualizations.put(page, canvas);
            }
            canvas.saveGraphicsState();
            canvas.setStrokingColor(color);
            canvas.addRect((float)box.getMinX(), (float)box.getMinY(), (float)box.getWidth(), (float)box.getHeight());
            canvas.stroke();
            canvas.restoreGraphicsState();
        }
    }
    return boxes;
}

(VisualizeMarkedContent方法)

方法 showContent 确定与给定 MCID 关联的文本的边界框，如果需要则递归。

Rectangle2D showContent(int mcid, Map<Integer, PDMarkedContent> theseMarkedContents) throws IOException {
    Rectangle2D box = null;
    PDMarkedContent markedContent = theseMarkedContents != null ? theseMarkedContents.get(mcid) : null;
    List<Object> contents = markedContent != null ? markedContent.getContents() : Collections.emptyList();
    StringBuilder textContent =  new StringBuilder();
    for (Object object : contents) {
        if (object instanceof TextPosition) {
            TextPosition textPosition = (TextPosition)object;
            textContent.append(textPosition.getUnicode());

            int[] codes = textPosition.getCharacterCodes();
            if (codes.length != 1) {
                System.out.printf("<!-- text position with unexpected number of codes: %d -->", codes.length);
            } else {
                box = union(box, calculateGlyphBounds(textPosition.getTextMatrix(), textPosition.getFont(), codes[0]).getBounds2D());
            }
        } else if (object instanceof PDMarkedContent) {
            PDMarkedContent thisMarkedContent = (PDMarkedContent) object;
            box = union(box, showContent(thisMarkedContent.getMCID(), theseMarkedContents));
        } else {
            textContent.append("?" + object);
        }
    }
    return box;
}

(VisualizeMarkedContent方法)

前两个方法 showStructure 和 showContent 使用以下帮助器来构建边界框的(逐页)联合:

Map<PDPage, Rectangle2D> union(Map<PDPage, Rectangle2D>... maps) {
    Map<PDPage, Rectangle2D> result = null;
    for (Map<PDPage, Rectangle2D> map : maps) {
        if (map != null) {
            if (result != null) {
                for (Map.Entry<PDPage, Rectangle2D> entry : map.entrySet()) {
                    PDPage page = entry.getKey();
                    Rectangle2D rectangle = union(result.get(page), entry.getValue());
                    if (rectangle != null)
                        result.put(page, rectangle);
                }
            } else {
                result = map;
            }
        }
    }
    return result;
}

Map<PDPage, Rectangle2D> union(Map<PDPage, Rectangle2D> map, PDPage page, Rectangle2D rectangle) {
    if (map == null)
        map = new HashMap<>();
    map.put(page, union(map.get(page), rectangle));
    return map;
}

Rectangle2D union(Rectangle2D... rectangles)
{
    Rectangle2D box = null;
    for (Rectangle2D rectangle : rectangles) {
        if (rectangle != null) {
            if (box != null)
                box.add(rectangle);
            else
                box = rectangle;
        }
    }
    return box;
}

(VisualizeMarkedContent辅助方法)

最后，从 PDFBox 示例 DrawPrintTextLocations 借用了方法 calculateGlyphBounds 来计算各个字形边界框:

private Shape calculateGlyphBounds(Matrix textRenderingMatrix, PDFont font, int code) throws IOException
{
    GeneralPath path = null;
    AffineTransform at = textRenderingMatrix.createAffineTransform();
    at.concatenate(font.getFontMatrix().createAffineTransform());
    if (font instanceof PDType3Font)
    {
        // It is difficult to calculate the real individual glyph bounds for type 3 fonts
        // because these are not vector fonts, the content stream could contain almost anything
        // that is found in page content streams.
        PDType3Font t3Font = (PDType3Font) font;
        PDType3CharProc charProc = t3Font.getCharProc(code);
        if (charProc != null)
        {
            BoundingBox fontBBox = t3Font.getBoundingBox();
            PDRectangle glyphBBox = charProc.getGlyphBBox();
            if (glyphBBox != null)
            {
                // PDFBOX-3850: glyph bbox could be larger than the font bbox
                glyphBBox.setLowerLeftX(Math.max(fontBBox.getLowerLeftX(), glyphBBox.getLowerLeftX()));
                glyphBBox.setLowerLeftY(Math.max(fontBBox.getLowerLeftY(), glyphBBox.getLowerLeftY()));
                glyphBBox.setUpperRightX(Math.min(fontBBox.getUpperRightX(), glyphBBox.getUpperRightX()));
                glyphBBox.setUpperRightY(Math.min(fontBBox.getUpperRightY(), glyphBBox.getUpperRightY()));
                path = glyphBBox.toGeneralPath();
            }
        }
    }
    else if (font instanceof PDVectorFont)
    {
        PDVectorFont vectorFont = (PDVectorFont) font;
        path = vectorFont.getPath(code);

        if (font instanceof PDTrueTypeFont)
        {
            PDTrueTypeFont ttFont = (PDTrueTypeFont) font;
            int unitsPerEm = ttFont.getTrueTypeFont().getHeader().getUnitsPerEm();
            at.scale(1000d / unitsPerEm, 1000d / unitsPerEm);
        }
        if (font instanceof PDType0Font)
        {
            PDType0Font t0font = (PDType0Font) font;
            if (t0font.getDescendantFont() instanceof PDCIDFontType2)
            {
                int unitsPerEm = ((PDCIDFontType2) t0font.getDescendantFont()).getTrueTypeFont().getHeader().getUnitsPerEm();
                at.scale(1000d / unitsPerEm, 1000d / unitsPerEm);
            }
        }
    }
    else if (font instanceof PDSimpleFont)
    {
        PDSimpleFont simpleFont = (PDSimpleFont) font;

        // these two lines do not always work, e.g. for the TT fonts in file 032431.pdf
        // which is why PDVectorFont is tried first.
        String name = simpleFont.getEncoding().getName(code);
        path = simpleFont.getPath(name);
    }
    else
    {
        // shouldn't happen, please open issue in JIRA
        System.out.println("Unknown font class: " + font.getClass());
    }
    if (path == null)
    {
        return null;
    }
    return at.createTransformedShape(path.getBounds2D());
}

(VisualizeMarkedContent方法)

示例文档的结果: