Convert an Image to Grayscale PDF for Better OCR in C# or Java

Apryse

image

pdf conversion

ocr

pdf

Pre-processing is a critical step in improving the accuracy and quality of OCR results, and that may be why many developers are looking for the best way to convert an image to a black & white PDF file, to more easily import a better-quality file into OCR for text data extraction. With Apryse SDK, it’s easy to convert images to grayscale PDF.

We’ve included sample code showing how to complete this using C# and Java below.

C#

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using pdftron; 
using pdftron.Common; 
using pdftron.PDF; 
using pdftron.SDF; 
 
namespace ConsoleApp1 
{ 
    internal class Program 
    { 
        static void Main(string[] args) 
        { 
            try { 
 
                PDFNet.Initialize("your_license_key"); 
 
                string inputPath = "path_to_input_image"; 
                string exportGrayScalePath = "grayscale.jpg"; 
 
                PDFDoc doc = new PDFDoc(); 
                Page page = WritePage(doc, inputPath); 
                PDFDraw draw = new PDFDraw(300); 
                ObjSet hint_set = new ObjSet(); 
                Obj gray_hint = hint_set.CreateDict(); 
                gray_hint.PutName("ColorSpace", "Gray"); 
 
                draw.Export(page, exportGrayScalePath, "JPEG", gray_hint); 
 
                doc.Close(); 
 
                PDFDoc grayDoc = new PDFDoc(); 
                WritePage(grayDoc, exportGrayScalePath); 
 
                // Save the PDF 
                grayDoc.Save("grayscale.pdf", SDFDoc.SaveOptions.e_linearized); 
                grayDoc.Close(); 
 
                Console.WriteLine("Image converted to greyscale and added to PDF successfully!"); 
 
            } 
            catch (PDFNetException e) 
            { 
                Console.WriteLine(e.Message); 
            } 
        } 
 
        static Page WritePage(PDFDoc doc, string imageFile)  
        { 
            ElementBuilder builder = new ElementBuilder(); 
            ElementWriter writer = new ElementWriter(); 
            Image img = Image.Create(doc, imageFile); 
            Page page = doc.PageCreate(new Rect(0, 0, img.GetImageWidth(), img.GetImageHeight())); 
            writer.Begin(page); 
            Element element = builder.CreateImage(img, 0, 0, img.GetImageWidth(), img.GetImageHeight()); 
            writer.WritePlacedElement(element); 
            writer.End(); 
            doc.PagePushBack(page); 
 
            return page; 
        } 
    } 
}

Java

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import com.pdftron.common.PDFNetException; 
import com.pdftron.pdf.*; 
import com.pdftron.sdf.*; 
 
public class App { 
public static void main(String[] args) { 
  try { 
    PDFNet.initialize("your_license_key"); 
 
    String inputPath = "path_to_input_image"; 
    String exportGrayScalePath = "src\\samples\\grayscale.jpg"; 
 
    PDFDoc doc = new PDFDoc(); 
    Page page = writePage(doc, inputPath); 
    PDFDraw draw = new PDFDraw(); 
    draw.setDPI(300); 
    ObjSet hintSet = new ObjSet(); 
    Obj grayHint = hintSet.createDict(); 
    grayHint.putName("ColorSpace", "Gray"); 
 
    draw.export(page, exportGrayScalePath, "JPEG", grayHint); 
 
    doc.close(); 
 
    PDFDoc grayDoc = new PDFDoc(); 
    writePage(grayDoc, exportGrayScalePath); 
 
    // Save the PDF 
    grayDoc.save("src\\samples\\grayscale.pdf", SDFDoc.SaveMode.LINEARIZED, null); 
    grayDoc.close(); 
 
    System.out.println("Image converted to grayscale and added to PDF successfully!"); 
 
  } catch (PDFNetException e) { 
    System.out.println(e.getMessage()); 
  } 
  } 
 
  static Page writePage(PDFDoc doc, String imageFile) throws PDFNetException { 
    ElementBuilder builder = new ElementBuilder(); 
    ElementWriter writer = new ElementWriter(); 
    Image img = Image.create(doc, imageFile); 
    Page page = doc.pageCreate(new Rect(0, 0, img.getImageWidth(), img.getImageHeight())); 
    writer.begin(page); 
    Element element = builder.createImage(img, 0, 0, img.getImageWidth(), img.getImageHeight()); 
    writer.writePlacedElement(element); 
    writer.end(); 
    doc.pagePushBack(page); 
 
    return page; 
  } 
}

Build reliable TIFF-to-PDF conversion in Java using the Apryse SDK — get started today!

Next Steps

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Learn how to convert JPEG to PDF in C#.