PDF image JBIG2 compression in Swift (lossy & lossless)

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

import PDFNet
import Foundation

// 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:
//   http://www.pdftron.com/net/samplecode/data/US061222892.pdf
//
func runJBIG2Test() -> Int {
    return autoreleasepool {
        
        
        do {
            try PTPDFNet.catchException {
                let pdf_doc: PTPDFDoc = PTPDFDoc(filepath: Bundle.main.path(forResource: "US061222892-a", ofType: "pdf"))
                pdf_doc.initSecurityHandler()
                
                let cos_doc: PTSDFDoc = pdf_doc.getSDFDoc()
                let num_objs = cos_doc.xRefSize()
                for i in 1..<num_objs {
                    guard let obj: PTObj = cos_doc.getObj(UInt32(i)) else {
                        continue
                    }
                    if !obj.isFree() && obj.isStream() {
                        // Process only images
                        var itr: PTDictIterator = obj.find("Subtype")
                        if !itr.hasNext() || !(itr.value().getName() == "Image") {
                            continue
                        }
                        
                        let input_image: PTImage = PTImage(image_xobject: obj)
                        // Process only gray-scale images
                        if input_image.getComponentNum() != 1 {
                            continue
                        }
                        let bpc: Int32 = input_image.getBitsPerComponent()
                        if bpc != 1 {
                            // Recompress only 1 BPC images
                            continue
                        }
                        
                        // Skip images that are already compressed using JBIG2
                        itr = obj.find("Filter")
                        if itr.hasNext() && itr.value().isName() && (itr.value().getName() == "JBIG2Decode") {
                            continue
                        }
                        
                        let filter: PTFilter = obj.getDecodedStream()
                        let reader = PTFilterReader(filter: filter)
                        
                        let hint_set: PTObjSet = PTObjSet()   // A hint to image encoder to use JBIG2 compression
                        let hint: PTObj = hint_set.createArray()
                        
                        hint.pushBackName("JBIG2")
                        hint.pushBackName("Lossless")
                        
                        let new_image: PTImage = PTImage.create(withFilterData: cos_doc, image_data: reader, width: input_image.getWidth(), height: input_image.getHeight(), bpc: 1, color_space: PTColorSpace.createDeviceGray(), encoder_hints: hint)
                        
                        let new_img_obj: PTObj = new_image.getSDFObj()
                        itr = obj.find("Decode")
                        if itr.hasNext() {
                            new_img_obj.put("Decode", obj: itr.value())
                        }
                        itr = obj.find("ImageMask")
                        if itr.hasNext() {
                            new_img_obj.put("ImageMask", obj: itr.value())
                        }
                        itr = obj.find("Mask")
                        if itr.hasNext() {
                            new_img_obj.put("Mask", obj: itr.value())
                        }
                        
                        cos_doc.swap(UInt32(i), obj_num2: new_img_obj.getNum())
                    }
                }
                
                pdf_doc.save(toFile: URL(fileURLWithPath: NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]).appendingPathComponent("US061222892_JBIG2.pdf").path, flags: e_ptremove_unused.rawValue)
            }
        } catch let e as NSError {
            print("\(e)")
            print("Please make sure that the pathname to the test file is correct.")
        }
        
        print("Done.")
        
        return 0
    }
}