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Add feature to merge a hocr file into a existing pdf file
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@manuel-ssg
manuel-ssg committed Nov 27, 2023
1 parent 17bea68 commit 9817036
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298 changes: 298 additions & 0 deletions src/main/java/net/sourceforge/tess4j/util/Hocr2PdfParser.java
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package net.sourceforge.tess4j.util;

import org.apache.commons.io.IOUtils;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageContentStream;
import org.apache.pdfbox.pdmodel.common.PDRectangle;
import org.apache.pdfbox.pdmodel.font.PDFont;
import org.apache.pdfbox.pdmodel.font.PDType1Font;
import org.apache.pdfbox.pdmodel.font.Standard14Fonts;
import org.apache.pdfbox.pdmodel.graphics.state.RenderingMode;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.xml.sax.*;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.awt.*;
import java.io.*;
import java.util.HashMap;
import java.util.Map;

import static java.lang.Float.valueOf;

public class Hocr2PdfParser implements ContentHandler, ErrorHandler {
private static final Logger logger = LoggerFactory.getLogger(new LoggHelper().toString());
public static final String SPACE = " ";
public static final String BBOX = "bbox";
public static final String TITLE = "title";
public static final String SEMICOL = ";";
public static final String DIV = "div";
public static final String SPAN = "span";
public static final String OCRX_WORD = "ocrx_word";
public static final String OCR_WORD = "ocr_word";
public static final String OCR_LINE = "ocr_line";
public static final String CLASS = "class";
public static final String OCR_PAGE = "ocr_page";

private final RenderingMode renderingMode;
private final PDFont font;
private final boolean useHocrLineToY;
private float xPageScaling;
private float yPageScaling;
private final StringBuilder text = new StringBuilder();
private String[] coordsText;
private String[] coordsLine;
private PDPageContentStream pdfPageCanvas = null;
private PDRectangle pdfPageBBox = null;
private final PDDocument pdDocument;
private final String hocrFilepath;

@Override
public void setDocumentLocator(Locator locator) {
//nothing to do
}

@Override
public void startDocument() throws SAXException {
//nothing to do
}

@Override
public void endDocument() throws SAXException {
finishCurrentPage();
}

@Override
public void startPrefixMapping(String prefix, String uri) throws SAXException {
//nothing to do
}

@Override
public void endPrefixMapping(String prefix) throws SAXException {
//nothing to do
}

@Override
public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
text.setLength(0);
this.coordsText = null;
final String klass = atts.getValue(CLASS);
if (SPAN.equals(qName) || SPAN.equals(localName)) {
logger.debug("start of span, there is a new text or line");

if (OCRX_WORD.equals(klass) || OCR_WORD.equals(klass)) {
this.coordsText = readBboxCoordsFromAttributs(atts);
} else if (OCR_LINE.equals(klass)) {
this.coordsLine = readBboxCoordsFromAttributs(atts);
} else {
logger.debug("ignore {0} : {1}", new Object[]{CLASS, klass});
}
} else if (DIV.equals(qName) || DIV.equals(localName)) {
if (OCR_PAGE.equals(klass)) {
logger.debug("start div, start of page and close the previous page");
finishCurrentPage();
beginNewPage(
convertHocrAttributsToPageNum(atts),
readBboxCoordsFromAttributs(atts)
);
} else {
logger.debug("ignore {0} : {1}", new Object[]{CLASS, klass});
}
} else {
logger.debug("ignore qName : {0} or localName :{1} ", new Object[]{qName, localName});
}
}

@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
if (coordsText != null && text.length() > 0) {
logger.debug("OCRed word span closed, coords: {0} {1}", new Object[]{coordsText, text});

if(useHocrLineToY) {
//Override text coords by line coords for Y
coordsText[2] = coordsLine[2];
coordsText[4] = coordsLine[4];
}

addTextToPDF(coordsText, text.toString());
} else {
logger.debug("ignore endElement no text readed");
}
coordsText = null;
}

@Override
public void characters(char[] ch, int start, int length) throws SAXException {
text.append(ch, start, length);
}

@Override
public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException {
//nothing to do
}

@Override
public void processingInstruction(String target, String data) throws SAXException {
//nothing to do
}

@Override
public void skippedEntity(String name) throws SAXException {
//nothing to do
}

@Override
public void warning(SAXParseException exception) throws SAXException {
logger.warn("warning: " + exception.getMessage());
}

@Override
public void error(SAXParseException exception) throws SAXException {
logger.error("error: " + exception.getMessage());
}

@Override
public void fatalError(SAXParseException exception) throws SAXException {
logger.error("fatalError: " + exception.getMessage());
}

private String[] readBboxCoordsFromAttributs(Attributes attributes) {
String title = attributes.getValue(TITLE);
int bboxStart = title.indexOf(BBOX);
int bboxEnd = title.indexOf(SEMICOL, bboxStart);
return title.substring(bboxStart, bboxEnd).split(SPACE);
}

private Integer convertHocrAttributsToPageNum(Attributes atts) {
final String pageId = atts.getValue("id");
return Integer.valueOf(pageId.split("_")[1], 10) - 1;
}

private void beginNewPage(Integer pageId, String hocrPageBbox[]) throws SAXException {
try {
final PDPage sourcePage = pdDocument.getPage(pageId);

this.pdfPageBBox = sourcePage.getBBox();
this.pdfPageCanvas = new PDPageContentStream(
this.pdDocument,
sourcePage,
PDPageContentStream.AppendMode.APPEND,
true,
true);
float hocrImgWidth = valueOf(hocrPageBbox[3]) - valueOf(hocrPageBbox[1]);
float hocrImgHeight = valueOf(hocrPageBbox[4]) - valueOf(hocrPageBbox[2]);
this.xPageScaling = this.pdfPageBBox.getWidth() / hocrImgWidth;
this.yPageScaling = this.pdfPageBBox.getHeight() / hocrImgHeight;

logger.debug("Load page {0} with scaling {1}x{2}",
new Object[]{pageId, this.xPageScaling, this.yPageScaling});

} catch (NumberFormatException | IOException e) {
throw new SAXException(e.getMessage());
}
}

private void finishCurrentPage() {
if (this.pdfPageCanvas != null) {
IOUtils.closeQuietly(this.pdfPageCanvas);
}
}

public void addTextToPDF(String[] imgCoords, String text) throws SAXException {
try {
PDRectangle textRect = new PDRectangle(
Integer.valueOf(imgCoords[1]),
Integer.valueOf(imgCoords[4]),
Integer.valueOf(imgCoords[3]) - Integer.valueOf(imgCoords[1]),
Integer.valueOf(imgCoords[4]) - Integer.valueOf(imgCoords[2])
);

float expectedTextWidth = textRect.getWidth() * xPageScaling;
float fontSize = expectedTextWidth * 1000 / font.getStringWidth(text);
float xText = textRect.getLowerLeftX() * xPageScaling;
float yText = pdfPageBBox.getHeight() - textRect.getLowerLeftY() * yPageScaling;

printTextAtCoordinates(text, fontSize, xText, yText);
} catch (IOException e) {
throw new SAXException(e.getMessage());
}
}

private void printTextAtCoordinates(String text, float fontSize, float xText, float yText) throws IOException {
logger.debug("Text,{1},{2},{3},{4},{5},{6}",
new Object[]{xText, yText, fontSize, pdfPageBBox.getWidth(), pdfPageBBox.getHeight(), text});

pdfPageCanvas.setFont(font, fontSize);
pdfPageCanvas.saveGraphicsState();
pdfPageCanvas.beginText();
pdfPageCanvas.setRenderingMode(this.renderingMode);
pdfPageCanvas.setNonStrokingColor(Color.red);
pdfPageCanvas.setLineWidth(0);
pdfPageCanvas.newLineAtOffset(xText, yText);
pdfPageCanvas.showText(text);
pdfPageCanvas.endText();
pdfPageCanvas.restoreGraphicsState();
}

public Hocr2PdfParser(String hocrFilepath, PDDocument pdDocument, boolean visible, boolean useHocrLineToY, String fontName) throws IOException {
this.hocrFilepath = hocrFilepath;
this.pdDocument = pdDocument;
this.useHocrLineToY = useHocrLineToY;

if (visible) {
this.renderingMode = RenderingMode.FILL;
} else {
this.renderingMode = RenderingMode.NEITHER;
}
if (fontName != null) {
this.font = new PDType1Font(Standard14Fonts.FontName.valueOf(fontName));
} else {
this.font = new PDType1Font(Standard14Fonts.FontName.HELVETICA);
}
}

public void parse() throws SAXException, IOException, ParserConfigurationException {

SAXParserFactory parserFactory = SAXParserFactory.newInstance();
SAXParser parser = parserFactory.newSAXParser();
XMLReader reader = parser.getXMLReader();
reader.setContentHandler(this);
reader.setErrorHandler(this);

reader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
reader.setFeature("http://javax.xml.XMLConstants/feature/secure-processing", false);

try (FileInputStream fileInputStream = new FileInputStream(this.hocrFilepath)) {
final BufferedReader characterStream = new BufferedReader(new InputStreamReader(fileInputStream, "UTF8"));
characterStream.readLine();
Reader filter = new Reader() {
@Override
public int read(char[] cbuf, int off, int len) throws IOException {
int chars = characterStream.read(cbuf, off, len);
// filter out all non XML characters
for (int i = 0; i < chars; i++) {
int c = cbuf[i + off];
if (c == 0x0009 || c == 0x000A || c == 0x000D
|| (c >= 0x0020 && c <= 0xD7FF)
|| (0x10000 <= c && c <= 0x10FFFF)) {
// c is XML valid, leave it alone
} else {
cbuf[i + off] = ' ';
}
}
return chars;
}

@Override
public void close() throws IOException {
characterStream.close();
}
};
reader.parse(new InputSource(filter));
}
}

}
28 changes: 28 additions & 0 deletions src/main/java/net/sourceforge/tess4j/util/PdfBoxUtilities.java
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Expand Up @@ -15,6 +15,14 @@
*/
package net.sourceforge.tess4j.util;

import org.apache.pdfbox.multipdf.PDFMergerUtility;
import org.apache.pdfbox.multipdf.Splitter;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.rendering.ImageType;
import org.apache.pdfbox.rendering.PDFRenderer;
import org.apache.pdfbox.tools.imageio.ImageIOUtil;
import org.slf4j.LoggerFactory;

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FilenameFilter;
Expand Down Expand Up @@ -220,4 +228,24 @@ public static void mergePdf(File[] inputPdfFiles, File outputPdfFile) {
logger.error("Error counting PDF pages => " + ioe);
}
}

/**
* Merge text from hocr file into a pdf
* @param inputHocr input hocr file
* @param inputPdfStr input pdf file
* @param outputPdfStr ouput pdf file result of merging
* @param visible does the text are visible or not
* @throws Exception
*/
public static void mergeHocrIntoAPdf(String inputHocr, String inputPdfStr, String outputPdfStr, boolean visible) throws Exception {
try (
PDDocument pdDocument = Loader.loadPDF(new File(inputPdfStr))
) {
final Hocr2PdfParser hocr2PdfParser = new Hocr2PdfParser(inputHocr, pdDocument, visible, false, null);

hocr2PdfParser.parse();

pdDocument.save(outputPdfStr);
}
}
}
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