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/*
This file is part of the iText (R) project.
Copyright (c) 1998-2024 Apryse Group NV
Authors: Apryse Software.
This program is offered under a commercial and under the AGPL license.
For commercial licensing, contact us at https://itextpdf.com/sales. For AGPL licensing, see below.
AGPL licensing:
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see
* This class provides possibilities to use features of "tesseract"
* using tess4j.
*
*
* Please note that this class is not thread-safe, in other words this Tesseract engine cannot
* be used for multithreaded processing. You should create one instance per thread
*/
public class Tesseract4LibOcrEngine extends AbstractTesseract4OcrEngine {
/**
* {@link net.sourceforge.tess4j.ITesseract} Instance.
* (depends on OS type)
*/
private ITesseract tesseractInstance = null;
/**
* Pattern for matching ASCII string.
*/
private static final Pattern ASCII_STRING_PATTERN = Pattern.compile("^[\\u0000-\\u007F]*$");
/**
* Creates a new {@link Tesseract4LibOcrEngine} instance.
*
* @param tesseract4OcrEngineProperties set of properteis
*/
public Tesseract4LibOcrEngine(
final Tesseract4OcrEngineProperties tesseract4OcrEngineProperties) {
super(tesseract4OcrEngineProperties);
tesseractInstance = TesseractOcrUtil
.initializeTesseractInstance(isWindows(), null,
null, null);
}
/**
* Gets tesseract instance.
*
* @return initialized {@link net.sourceforge.tess4j.ITesseract} instance
*/
public ITesseract getTesseractInstance() {
return tesseractInstance;
}
/**
* Initializes instance of tesseract if it haven't been already
* initialized or it have been disposed and sets all the required
* properties.
*
* @param outputFormat selected {@link OutputFormat} for tesseract
*/
public void initializeTesseract(final OutputFormat outputFormat) {
if (getTesseractInstance() == null
|| TesseractOcrUtil
.isTesseractInstanceDisposed(getTesseractInstance())) {
tesseractInstance = TesseractOcrUtil
.initializeTesseractInstance(isWindows(), getTessData(),
getLanguagesAsString(),
getTesseract4OcrEngineProperties()
.getPathToUserWordsFile());
}
getTesseractInstance()
.setTessVariable("tessedit_create_hocr",
outputFormat.equals(OutputFormat.HOCR) ? "1" : "0");
if (getTesseract4OcrEngineProperties().isUseTxtToImproveHocrParsing()) {
getTesseractInstance().setTessVariable("preserve_interword_spaces", "1");
}
getTesseractInstance().setTessVariable("user_defined_dpi", "300");
if (getTesseract4OcrEngineProperties()
.getPathToUserWordsFile() != null) {
getTesseractInstance()
.setTessVariable("load_system_dawg", "0");
getTesseractInstance()
.setTessVariable("load_freq_dawg", "0");
getTesseractInstance()
.setTessVariable("user_words_suffix",
getTesseract4OcrEngineProperties()
.getDefaultUserWordsSuffix());
getTesseractInstance()
.setTessVariable("user_words_file",
getTesseract4OcrEngineProperties()
.getPathToUserWordsFile());
}
TesseractOcrUtil.setTesseractProperties(getTesseractInstance(),
getTessData(), getLanguagesAsString(),
getTesseract4OcrEngineProperties().getPageSegMode(),
getTesseract4OcrEngineProperties().getPathToUserWordsFile());
}
/**
* Performs tesseract OCR using wrapper for Tesseract OCR API for the selected page
* of input image (by default 1st).
*
* Please note that list of output files is accepted instead of a single file because
* page number parameter is not respected in case of TIFF images not requiring preprocessing.
* In other words, if the passed image is the TIFF image and according to the {@link Tesseract4OcrEngineProperties}
* no preprocessing is needed, each page of the TIFF image is OCRed and the number of output files in the list
* is expected to be same as number of pages in the image, otherwise, only one file is expected
*
* @param inputImage input image {@link java.io.File}
* @param outputFiles {@link java.util.List} of output files
* (one per each page)
* @param outputFormat selected {@link OutputFormat} for tesseract
* @param pageNumber number of page to be processed
* @param dispatchEvent indicates if event needs to be dispatched
* @param eventHelper event helper
*/
void doTesseractOcr(final File inputImage,
final List outputFiles, final OutputFormat outputFormat,
final int pageNumber, final boolean dispatchEvent, AbstractPdfOcrEventHelper eventHelper) {
PdfOcrTesseract4ProductEvent event = null;
if (eventHelper == null) {
eventHelper = new Tesseract4EventHelper();
}
// usage event
if (dispatchEvent) {
event = onEvent(eventHelper);
}
try {
// check tess data path for non ASCII characters
validateTessDataPath(getTessData());
validateLanguages(getTesseract4OcrEngineProperties()
.getLanguages());
initializeTesseract(outputFormat);
// if preprocessing is not needed and provided image is tiff,
// the image will be paginated and separate pages will be OCRed
List resultList = new ArrayList();
if (!getTesseract4OcrEngineProperties().isPreprocessingImages()
&& ImagePreprocessingUtil.isTiffImage(inputImage)) {
resultList = getOcrResultForMultiPage(inputImage,
outputFormat);
} else {
resultList.add(getOcrResultForSinglePage(inputImage,
outputFormat, pageNumber));
}
// list of result strings is written to separate files
// (one for each page)
for (int i = 0; i < resultList.size(); i++) {
String result = resultList.get(i);
File outputFile = i >= outputFiles.size()
? null : outputFiles.get(i);
if (result != null && outputFile != null) {
try (Writer writer = new OutputStreamWriter(
new FileOutputStream(outputFile.getAbsolutePath()),
StandardCharsets.UTF_8)) {
writer.write(result);
} catch (IOException e) {
throw new PdfOcrInputTesseract4Exception(
PdfOcrTesseract4ExceptionMessageConstant.CANNOT_WRITE_TO_FILE, e);
}
}
}
// statistics event
onEventStatistics(eventHelper);
// confirm on_demand event
if (event != null && event.getConfirmationType() == EventConfirmationType.ON_DEMAND) {
eventHelper.onEvent(new ConfirmEvent(event));
}
} catch (PdfOcrTesseract4Exception e) {
LoggerFactory.getLogger(getClass())
.error(e.getMessage());
throw new PdfOcrTesseract4Exception(e.getMessage(), e);
} finally {
if (tesseractInstance != null) {
TesseractOcrUtil.disposeTesseractInstance(tesseractInstance);
}
if (getTesseract4OcrEngineProperties().getPathToUserWordsFile()
!= null
&& getTesseract4OcrEngineProperties().isUserWordsFileTemporary()) {
TesseractHelper.deleteFile(
getTesseract4OcrEngineProperties()
.getPathToUserWordsFile());
}
}
}
/**
* Validates Tess Data path,
* checks if tess data path contains only ASCII charset.
* Note: tesseract lib has issues with non ASCII characters in tess data path.
*
* @param tessDataPath {@link java.lang.String} path to tess data
*/
private static void validateTessDataPath(final String tessDataPath) {
Matcher asciiStringMatcher = ASCII_STRING_PATTERN.matcher(tessDataPath);
if (!asciiStringMatcher.matches()) {
throw new PdfOcrTesseract4Exception(
PdfOcrTesseract4ExceptionMessageConstant
.PATH_TO_TESS_DATA_DIRECTORY_CONTAINS_NON_ASCII_CHARACTERS);
}
}
/**
* Gets OCR result from provided multi-page image and returns result as
* list of strings for each page. This method is used for tiff images
* when preprocessing is not needed.
*
* @param inputImage input image {@link java.io.File}
* @param outputFormat selected {@link OutputFormat} for tesseract
* @return list of result string that will be written to a temporary files
* later
*/
private List getOcrResultForMultiPage(final File inputImage,
final OutputFormat outputFormat) {
List resultList = new ArrayList();
try {
initializeTesseract(outputFormat);
TesseractOcrUtil util = new TesseractOcrUtil();
util.initializeImagesListFromTiff(inputImage);
int numOfPages = util.getListOfPages().size();
for (int i = 0; i < numOfPages; i++) {
String result = util.getOcrResultAsString(
getTesseractInstance(),
util.getListOfPages().get(i),
outputFormat);
resultList.add(result);
}
} catch (TesseractException e) {
String msg = MessageFormatUtil
.format(Tesseract4LogMessageConstant.TESSERACT_FAILED,
e.getMessage());
LoggerFactory.getLogger(getClass())
.error(msg);
throw new PdfOcrTesseract4Exception(
PdfOcrTesseract4ExceptionMessageConstant
.TESSERACT_FAILED);
} finally {
TesseractOcrUtil
.disposeTesseractInstance(getTesseractInstance());
}
return resultList;
}
/**
* Gets OCR result from provided single page image and preprocesses it if
* it is needed.
*
* @param inputImage input image {@link java.io.File}
* @param outputFormat selected {@link OutputFormat} for tesseract
* @param pageNumber number of page to be OCRed
* @return result as string that will be written to a temporary file later
*/
private String getOcrResultForSinglePage(final File inputImage,
final OutputFormat outputFormat,
final int pageNumber) {
String result = null;
try {
// preprocess if required
if (getTesseract4OcrEngineProperties().isPreprocessingImages()) {
// preprocess and try to ocr
result = new TesseractOcrUtil().getOcrResultAsString(
getTesseractInstance(),
ImagePreprocessingUtil
.preprocessImage(inputImage, pageNumber,
getTesseract4OcrEngineProperties().getImagePreprocessingOptions()),
outputFormat);
}
if (result == null) {
BufferedImage bufferedImage = ImagePreprocessingUtil
.readImage(inputImage);
if (bufferedImage != null) {
try {
result = new TesseractOcrUtil()
.getOcrResultAsString(getTesseractInstance(),
bufferedImage, outputFormat);
} catch (Exception e) {
LoggerFactory.getLogger(getClass())
.info(MessageFormatUtil.format(
Tesseract4LogMessageConstant
.CANNOT_PROCESS_IMAGE,
e.getMessage()));
}
}
if (result == null) {
// perform ocr using original input image
result = new TesseractOcrUtil()
.getOcrResultAsString(getTesseractInstance(),
inputImage, outputFormat);
}
}
} catch (Exception e) {
LoggerFactory.getLogger(getClass())
.error(MessageFormatUtil
.format(Tesseract4LogMessageConstant
.TESSERACT_FAILED,
e.getMessage()));
throw new PdfOcrTesseract4Exception(
PdfOcrTesseract4ExceptionMessageConstant
.TESSERACT_FAILED);
}
return result;
}
}