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PDF image JBIG2 compression in C++ (lossy & lossless)

Sample C++ code for using PDFTron SDK to recompress bitonal (black and white) images in existing PDF documents using JBIG2 compression (lossless or lossy). The sample is intended to show how to specify hint information for the image encoder and is not meant to be a generic PDF optimization tool. To demonstrate the possible compression rates, we recompressed a document containing 17 scanned pages. The original input document is ~1.4MB and is using standard CCITT Fax compression. Lossless JBIG2 compression shrunk the filesize to 641KB, while lossy JBIG2 compression shrunk it to 176KB.

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

#include <iostream>
#include <PDF/PDFNet.h>
#include <PDF/PDFDoc.h>
#include <PDF/ElementBuilder.h>
#include <Filters/FilterReader.h>
#include <SDF/ObjSet.h>

using namespace std;
using namespace pdftron;
using namespace Filters;
using namespace PDF;
using namespace SDF;
using namespace Common;

// This sample project illustrates how to recompress bi-tonal images in an 
// existing PDF document using JBIG2 compression. The sample is not intended 
// to be a generic PDF optimization tool.
// You can download the entire document using the following link:
int main(int argc, char *argv[]) 
		PDFDoc pdf_doc("../../TestFiles/US061222892-a.pdf");

		SDFDoc& cos_doc = pdf_doc.GetSDFDoc();
		int num_objs = cos_doc.XRefSize();
		for(int i=1; i<num_objs; ++i) 
			Obj obj = cos_doc.GetObj(i);
			if(obj && !obj.IsFree() && obj.IsStream()) 
				// Process only images
				DictIterator itr = obj.Find("Subtype");
				if(!itr.HasNext() || strcmp(itr.Value().GetName(), "Image"))
				Image input_image(obj);
				// Process only gray-scale images
				if(input_image.GetComponentNum() != 1)
				int bpc = input_image.GetBitsPerComponent();
				if(bpc != 1)	// Recompress only 1 BPC images

				// Skip images that are already compressed using JBIG2
				itr = obj.Find("Filter");
				if (itr.HasNext() && itr.Value().IsName() && 
					!strcmp(itr.Value().GetName(), "JBIG2Decode")) continue; 

				Filter filter=obj.GetDecodedStream();
				FilterReader reader(filter);

				ObjSet hint_set; 	// A hint to image encoder to use JBIG2 compression
				Obj hint=hint_set.CreateArray();

				Image new_image = Image::Create(cos_doc, reader, 
					input_image.GetImageHeight(), 1, ColorSpace::CreateDeviceGray(), hint);

				Obj new_img_obj = new_image.GetSDFObj();
				itr = obj.Find("Decode");
					new_img_obj.Put("Decode", itr.Value());
				itr = obj.Find("ImageMask");
				if (itr.HasNext())
					new_img_obj.Put("ImageMask", itr.Value());
				itr = obj.Find("Mask");
				if (itr.HasNext())
					new_img_obj.Put("Mask", itr.Value());

				cos_doc.Swap(i, new_img_obj.GetObjNum());

		pdf_doc.Save("../../TestFiles/Output/US061222892_JBIG2.pdf", SDFDoc::e_remove_unused, 0);
	catch(Common::Exception& e)
		cout << e << endl;
		cout << "Please make sure that the pathname to the test file is correct." << endl;
		cout << "Unknown Exception" << endl;

	return 0;

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