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Sample Go code shows how to use the Apryse OCR module on scanned documents in multiple languages. The OCR module can make searchable PDFs and extract scanned text for further indexing. Learn more about our Go PDF Library.
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//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2024 by Apryse Software Inc. All Rights Reserved.
// Consult LICENSE.txt regarding license information.
//---------------------------------------------------------------------------------------
package main
import (
"fmt"
"testing"
"flag"
. "github.com/pdftron/pdftron-go/v2"
)
var licenseKey string
var modulePath string
func init() {
flag.StringVar(&licenseKey, "license", "", "License key for Apryse SDK")
flag.StringVar(&modulePath, "modulePath", "", "Path for downloaded modules")
}
// Relative path to the folder containing test files.
var inputPath = "../TestFiles/OCR/"
var outputPath = "../TestFiles/Output/"
// ---------------------------------------------------------------------------------------
// The following sample illustrates how to use OCR module
// --------------------------------------------------------------------------------------
func TestOCR(t *testing.T){
// 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.
PDFNetInitialize(licenseKey)
// The location of the OCR Module
PDFNetAddResourceSearchPath(modulePath);
if ! OCRModuleIsModuleAvailable(){
fmt.Println("Unable to run OCRTest: PDFTron SDK OCR module not available.\n" +
"---------------------------------------------------------------\n" +
"The OCR module is an optional add-on, available for download\n" +
"at https://dev.apryse.com/. If you have already downloaded this\n" +
"module, ensure that the SDK is able to find the required files\n" +
"using the PDFNet::AddResourceSearchPath() function.")
}else{
// Example 1) Process image without specifying options, default language - English - is used
// --------------------------------------------------------------------------------
// A) Setup empty destination doc
doc := NewPDFDoc()
// B) Run OCR on the .png with options
ocrOpts := NewOCROptions()
OCRModuleImageToPDF(doc, inputPath + "psychomachia_excerpt.png", ocrOpts)
// C) Check the result
doc.Save(outputPath + "psychomachia_excerpt.pdf", uint(0))
fmt.Println("Example 1: psychomachia_excerpt.png")
// Example 2) Process document using multiple languages
// --------------------------------------------------------------------------------
// A) Setup empty destination doc
doc = NewPDFDoc()
// B) Setup options with multiple target languages, English will always be considered as secondary language
opts := NewOCROptions()
opts.AddLang("deu")
opts.AddLang("fra")
opts.AddLang("eng")
// C) Run OCR on the .jpg with options
OCRModuleImageToPDF(doc, inputPath + "multi_lang.jpg", opts)
// D) Check the result
doc.Save(outputPath + "multi_lang.pdf", uint(0))
fmt.Println("Example 2: multi_lang.jpg")
// Example 3) Process a .pdf specifying a language - German - and ignore zone comprising a sidebar image
// --------------------------------------------------------------------------------
// A) Open the .pdf document
doc = NewPDFDoc(inputPath + "german_kids_song.pdf")
// B) Setup options with a single language and an ignore zone
opts = NewOCROptions()
opts.AddLang("deu")
ignoreZones := NewRectCollection()
ignoreZones.AddRect(NewRect(424.0, 163.0, 493.0, 730.0))
opts.AddIgnoreZonesForPage(ignoreZones, 1)
// C) Run OCR on the .pdf with options
OCRModuleProcessPDF(doc, opts)
// D) check the result
doc.Save(outputPath + "german_kids_song.pdf", uint(0))
fmt.Println("Example 3: german_kids_song.pdf")
// Example 4) Process multi-page tiff with text/ignore zones specified for each page,
// optionally provide English as the target language
// --------------------------------------------------------------------------------
// A) Setup empty destination doc
doc = NewPDFDoc()
// B) Setup options with a single language plus text/ignore zones
opts = NewOCROptions()
opts.AddLang("eng")
ignoreZones = NewRectCollection()
// ignore signature box in the first 2 pages
ignoreZones.AddRect(NewRect(1492.0, 56.0, 2236.0, 432.0))
opts.AddIgnoreZonesForPage(ignoreZones, 1)
opts.AddIgnoreZonesForPage(ignoreZones, 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
ignoreZones.Clear()
ignoreZones.AddRect(NewRect(992.0, 1276.0, 1368.0, 1372.0))
opts.AddIgnoreZonesForPage(ignoreZones, 3)
textZones := NewRectCollection()
// we only have text zones selected in page 3
// select horizontal BUFFER ZONE sign
textZones.AddRect(NewRect(900.0, 2384.0, 1236.0, 2480.0))
// select right vertical BUFFER ZONE sign
textZones.AddRect(NewRect(1960.0, 1976.0, 2016.0, 2296.0))
// select Lot No.
textZones.AddRect(NewRect(696.0, 1028.0, 1196.0, 1128.0))
// select part of the plan inside the BUFFER ZONE
textZones.AddRect(NewRect(428.0, 1484.0, 1784.0, 2344.0))
textZones.AddRect(NewRect(948.0, 1288.0, 1672.0, 1476.0))
opts.AddTextZonesForPage(textZones, 3)
// C) Run OCR on the .pdf with options
OCRModuleImageToPDF(doc, inputPath + "bc_environment_protection.tif", opts)
// D) check the result
doc.Save(outputPath + "bc_environment_protection.pdf", uint(0))
fmt.Println("Example 4: bc_environment_protection.tif")
// 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
// --------------------------------------------------------------------------------
// A) Open the .pdf document
doc = NewPDFDoc(inputPath + "zero_value_test_no_text.pdf")
// B) Run OCR on the .pdf with default English language
opts = NewOCROptions()
json := OCRModuleGetOCRJsonFromPDF(doc, opts)
// C) Post-processing step (whatever it might be)
fmt.Println("Have OCR result JSON, re-applying to PDF")
OCRModuleApplyOCRJsonToPDF(doc, json)
// D) Check the result
doc.Save(outputPath + "zero_value_test_no_text.pdf", uint(0))
fmt.Println("Example 5: extracting and applying OCR JSON from zero_value_test_no_text.pdf")
// Example 6) The postprocessing workflow has also an option of extracting OCR results in XML format,
// similar to the one used by TextExtractor
// --------------------------------------------------------------------------------
// A) Setup empty destination doc
doc = NewPDFDoc()
// 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.
xml := OCRModuleGetOCRXmlFromImage(doc, inputPath + "physics.tif", opts)
// C) Post-processing step (whatever it might be)
fmt.Println("Have OCR result XML, re-applying to PDF")
OCRModuleApplyOCRXmlToPDF(doc, xml)
// D) Check the result
doc.Save(outputPath + "physics.pdf", uint(0))
fmt.Println("Example 6: extracting and applying OCR XML from physics.tif")
// Example 7) Resolution can be manually set, when DPI missing from metadata or is wrong
// --------------------------------------------------------------------------------
// A) Setup empty destination doc
doc = NewPDFDoc()
// B) Setup options with a text zone
opts = NewOCROptions()
textZones = NewRectCollection()
textZones.AddRect(NewRect(140.0, 870.0, 310.0, 920.0))
opts.AddTextZonesForPage(textZones, 1)
// C) Manually override DPI
opts.AddDPI(100)
// D) Run OCR on the .jpg with options
OCRModuleImageToPDF(doc, inputPath + "corrupted_dpi.jpg", opts)
// E) Check the result
doc.Save(outputPath + "corrupted_dpi.pdf", uint(0))
PDFNetTerminate()
fmt.Println("Example 7: converting image with corrupted resolution metadata corrupted_dpi.jpg to pdf with searchable text")
}
}