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Optimize & compress PDFs in Java

To optimize a PDF with default settings.

PDFDoc doc = new PDFDoc(filename);
Optimizer.optimize(doc);

Compress & optimize PDF files
Full code sample which shows how to use 'pdftron.PDF.Optimizer' to reduce PDF file size by removing redundant information and compressing data streams using the latest in image compression technology.

linkAbout optimize and compress

Compression as a subset of optimization represents encoding specific data using fewer bits than the original content by reducing the size of the data. This is distinct from optimize (which modifies all images) because you have the ability to choose individual images and to selectively choose the compression type for each.

PDFTron SDK supports all basic and advanced compression filters allowed in PDF including:

  • JPEG2000
  • JBIG2
  • CCITT Fax
  • Flate/PNG
  • JPEG/DCT
  • Crypt Filters

linkCompress images in a PDF document

To compress images using JBIG2 compression inside a PDF.

PDFDoc doc = new PDFDoc(filename);
SDFDoc cos_doc = pdf_doc.getSDFDoc();
int num_objs = (int) cos_doc.xRefSize();
for (int i = 1; i < num_objs; ++i) {
    Obj obj = cos_doc.getObj(i);
    if (obj == null || obj.isFree() || !obj.isStream())
        continue;

    // Process only images
    DictIterator itr = obj.find("Subtype");
    if (!itr.hasNext() || !itr.value().getName().equals("Image"))
        continue;

    Image input_image = new Image(obj);

    // Process only gray-scale images
    if (input_image.getComponentNum() != 1)
        continue;

    int bpc = 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().equals("JBIG2Decode")) 
        continue;

    Filter filter = obj.getDecodedStream();
    FilterReader reader = new FilterReader(filter);

    ObjSet hint_set = new ObjSet();
    Obj hint = hint_set.createArray(); // A hint to image encoder to use JBIG2 compression
    hint.pushBackName("JBIG2");
    hint.pushBackName("Lossless");

    Image new_image = Image.create(
        cos_doc, reader,
        input_image.getImageWidth(),
        input_image.getImageHeight(), 
        1, 
        ColorSpace.createDeviceGray(), 
        hint
    );
    cos_doc.swap(i, new_img.getSDFDoc().getObjNum());
}
const pdf_doc = await PDFNet.PDFDoc.createFromURL(filename);
pdf_doc.initSecurityHandler();

const cos_doc = await pdf_doc.getSDFDoc();
const num_objs = await cos_doc.xRefSize();
for (let i = 1; i < num_objs; ++i) {
    const obj = await cos_doc.getObj(i);
    if (obj && !(await obj.isFree()) && await obj.isStream()) {
        // Process only images
        var itr = await obj.find("Subtype");
        if (!(await itr.hasNext()) || await (await itr.value()).getName() !== "Image")
            continue;
        const input_image = await PDFNet.Image.createFromObj(obj);
        // Process only gray-scale images
        if (await input_image.getComponentNum() != 1)
            continue;
        if (await input_image.getBitsPerComponent() != 1) // Recompress only 1 BPC images
            continue;

        // Skip images that are already compressed using JBIG2
        itr = await obj.find("Filter");
        if (await itr.hasNext()) {
            const value = await itr.value();
            if (await value.isName() && await value.getName() === "JBIG2Decode") continue;
        }

        const filter = await obj.getDecodedStream();
        const reader = await PDFNet.FilterReader.create(filter);

        const hint_set = await PDFNet.ObjSet.create();
        const hint = await hint_set.createArray();

        hint.pushBackName("JBIG2");
        hint.pushBackName("Lossless");

        const new_image = await PDFNet.Image.createFromStream(cos_doc, reader, await input_image.getImageWidth(),
            await input_image.getImageHeight(), 1, await PDFNet.ColorSpace.createDeviceGray(), hint);

        const new_img_obj = await new_image.getSDFObj();
        itr = await obj.find("Decode");
        if (await itr.hasNext())
            new_img_obj.put("Decode", await itr.value());
        itr = await obj.find("ImageMask");
        if (await itr.hasNext())
            new_img_obj.put("ImageMask", await itr.value());
        itr = await obj.find("Mask");
        if (await itr.hasNext())
            new_img_obj.put("Mask", await itr.value());

        await cos_doc.swap(i, await new_img_obj.getObjNum());
    }
}

PDF image JBIG2 compression
Full sample code which illustrates how to recompress bitonal (black and white) images in existing PDF documents using JBIG2 compression.

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