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Java use OCR to make searchable PDFs and extract text

Sample Java code shows how to use the PDFTron OCR module on scanned documents in multiple languages. The OCR module can make searchable PDFs and extract scanned text for further indexing.

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//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2019 by PDFTron Systems Inc. All Rights Reserved.
// Consult legal.txt regarding legal and license information.
//---------------------------------------------------------------------------------------

import com.pdftron.sdf.Obj;
import com.pdftron.sdf.ObjSet;
import com.pdftron.sdf.SDFDoc;
import com.pdftron.pdf.*;

import com.pdftron.common.PDFNetException;

//---------------------------------------------------------------------------------------
// The following sample illustrates how to use OCR module
//---------------------------------------------------------------------------------------
public class OCRTest {
	public static void main(String[] args) {
		try {
			// The first step in every application using PDFNet is to initialize the
			// library and set the path to common PDF resources. The library is usually
			// initialized only once, but calling Initialize() multiple times is also fine.
			PDFNet.initialize();
			PDFNet.addResourceSearchPath("../../../Lib/");
			if( !OCRModule.isModuleAvailable() )
			{
				System.out.println("");
				System.out.println("Unable to run OCRTest: PDFTron SDK OCR module not available.");
				System.out.println("---------------------------------------------------------------");
				System.out.println("The OCR module is an optional add-on, available for download");
				System.out.println("at http://www.pdftron.com/. If you have already downloaded this");
				System.out.println("module, ensure that the SDK is able to find the required files");
				System.out.println("using the PDFNet.addResourceSearchPath() function.");
				System.out.println("");
				return;
			}

			// Relative path to the folder containing test files.
			String input_path = "../../TestFiles/OCR/";
			String output_path = "../../TestFiles/Output/";

			//--------------------------------------------------------------------------------
			// Example 1) Process image without specifying options, default language - English - is used
			try 
			{

				// A) Setup empty destination doc

				PDFDoc doc = new PDFDoc();

				// B) Run OCR on the .png with options

				OCRModule.imageToPDF(doc, input_path + "psychomachia_excerpt.png", null);

				// C) check the result

				doc.save(output_path + "psychomachia_excerpt.pdf", SDFDoc.SaveMode.LINEARIZED, null);
											
				doc.close();

				System.out.println("Example 1: psychomachia_excerpt.png");
				
			} catch (Exception e) {
				e.printStackTrace();
			}

			//--------------------------------------------------------------------------------
			// Example 2) Process document using multiple languages
			try 
			{

				// A) Setup empty destination doc

				PDFDoc doc = new PDFDoc();

				// B) Setup options with multiple target languages, English will always be considered as secondary language

				OCROptions options = new OCROptions();

				options.addLang("rus");
				options.addLang("deu");

				// C) Run OCR on the .jpg with options

				OCRModule.imageToPDF(doc, input_path + "multi_lang.jpg", options);

				// D) check the result

				doc.save(output_path + "multi_lang.pdf", SDFDoc.SaveMode.LINEARIZED, null);
											
				doc.close();

				System.out.println("Example 2: multi_lang.jpg");
				
			} catch (Exception e) {
				e.printStackTrace();
			}

			//--------------------------------------------------------------------------------
			// Example 3) Process a .pdf specifying a language - German - and ignore zone comprising a sidebar image 
			try 
			{

				// A) Open the .pdf document

				PDFDoc doc = new PDFDoc(input_path + "german_kids_song.pdf");

				// B) Setup options with a single language and an ignore zone

				OCROptions options = new OCROptions();
				options.addLang("deu");

				RectCollection zones = new RectCollection();
				zones.addRect(1768, 680, 2056, 3044);

				options.addIgnoreZonesForPage(zones, 1);

				// C) Run OCR on the .pdf with options

				OCRModule.processPDF(doc, options);
				
				// D) check the result

				doc.save(output_path + "german_kids_song.pdf", SDFDoc.SaveMode.LINEARIZED, null);
				
				doc.close();

				System.out.println("Example 3: german_kids_song.pdf");
				
			} catch (Exception e) {
				e.printStackTrace();
			}

			//--------------------------------------------------------------------------------
			// Example 4) Process multipage tiff with text/ignore zones specified for each page, optionally provide English as the target language

			try 
			{
				// A) Setup empty destination doc

				PDFDoc doc = new PDFDoc();

			   // B) Setup options with a single language plus text/ignore zones

				OCROptions options = new OCROptions();
				options.addLang("eng");

				RectCollection zones = new RectCollection();
				zones.addRect(1492, 56, 2236, 432);

				// ignore signature box in the first 2 pages
				options.addIgnoreZonesForPage(zones, 1);
				options.addIgnoreZonesForPage(zones, 2);

				// can use a combination of ignore and text boxes to focus on the page area of interest,
				// as ignore boxes are applied first, we remove the arrows before selecting part of the diagram
				zones.clear();
				zones.addRect(992, 1276, 1368, 1372);
				options.addIgnoreZonesForPage(zones, 3);

				// we only have text zones selected in page 3

				zones.clear();
				// select horizontal BUFFER ZONE sign
				zones.addRect(900, 2384, 1236, 2480);
				// select right vertical BUFFER ZONE sign
				zones.addRect(1960, 1976, 2016, 2296);
				// select Lot No.
				zones.addRect(696, 1028, 1196, 1128);

				// select part of the plan inside the BUFFER ZONE
				zones.addRect(428, 1484, 1784, 2344);
				zones.addRect(948, 1288, 1672, 1476);

				options.addTextZonesForPage(zones, 3);

				// C) Run OCR on the .tif with options

				OCRModule.imageToPDF(doc, input_path + "bc_environment_protection.tif", options);
				
				// D) check the result

				doc.save(output_path + "bc_environment_protection.pdf", SDFDoc.SaveMode.LINEARIZED, null);
				
				doc.close();

				System.out.println("Example 4: bc_environment_protection.tif");
				
			} catch (Exception e) {
				e.printStackTrace();
			}

			//--------------------------------------------------------------------------------
			// Example 5) Alternative workflow for extracting OCR result JSON, postprocessing (e.g., removing words not in the dictionary or filtering special
			// out special characters), and finally applying modified OCR JSON to the source PDF document 
			try 
			{

				// A) Open the .pdf document

				PDFDoc doc = new PDFDoc(input_path + "zero_value_test_no_text.pdf");

				// B) Run OCR on the .pdf with default English language

				String json = OCRModule.getOCRJsonFromPDF(doc, null);

				// C) Post-processing step (whatever it might be), but we just print json here

				System.out.println("Have OCR result JSON, re-applying to PDF");

				// D) Apply potentially modified OCR JSON to the PDF

				OCRModule.applyOCRJsonToPDF(doc, json);

				// E) Check the result

				doc.save(output_path + "zero_value_test_no_text.pdf", SDFDoc.SaveMode.LINEARIZED, null);

				doc.close();

				System.out.println("Example 5: extracting and applying OCR JSON from zero_value_test_no_text.pdf");
				
			} catch (Exception e) {
				e.printStackTrace();
			}

		//--------------------------------------------------------------------------------
		// Example 6) The postprocessing workflow has also an option of extracting OCR results in XML format, similar to the one used by TextExtractor
		try
		{

			// A) Setup empty destination doc

			PDFDoc doc = new PDFDoc();

			// B) Run OCR on the .tif with default English language, extracting OCR results in XML format. Note that
			// in the process we convert the source image into PDF. We reuse this PDF document later to add hidden text layer to it.

			String xml = OCRModule.getOCRXmlFromImage(doc, input_path + "physics.tif", null);

			// C) Post-processing step (whatever it might be), but we just print XML here

			System.out.println("Have OCR result XML, applying to PDF");

			// D) Apply potentially modified OCR XML to the PDF

			OCRModule.applyOCRXmlToPDF(doc, xml);

			// E) Check the result
		
			doc.save(output_path + "physics.pdf", SDFDoc.SaveMode.LINEARIZED, null);											
			doc.close();
			System.out.println("Example 6: extracting and applying OCR XML from physics.tif");

		}
		catch (Exception e) {
			e.printStackTrace();
		}

			// Calling Terminate when PDFNet is no longer in use is a good practice, but
			// is not required.
			PDFNet.terminate();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}
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