compress pdf with large images via java

Question

Looking for a way to compress images in a pdf and to output a pdf for archiving. I cannot compress the images before creation as it would compromise the quality of the print

Answer 1

I used code below for a proof of concept... Works a treat :) Thanks to Bruno for setting me on the right path :)

package compressPDF;

import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;

import javax.imageio.ImageIO;

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.PRStream;
import com.itextpdf.text.pdf.PdfName;
import com.itextpdf.text.pdf.PdfNumber;
import com.itextpdf.text.pdf.PdfObject;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfStamper;
import com.itextpdf.text.pdf.parser.PdfImageObject;

public class ResizeImage {

/** The resulting PDF file. */
//public static String RESULT = "results/part4/chapter16/resized_image.pdf";
/** The multiplication factor for the image. */
public static float FACTOR = 0.5f;

/**
 * Manipulates a PDF file src with the file dest as result
 * @param src the original PDF
 * @param dest the resulting PDF
 * @throws IOException
 * @throws DocumentException 
 */
public void manipulatePdf(String src, String dest) throws IOException, DocumentException {
    PdfName key = new PdfName("ITXT_SpecialId");
    PdfName value = new PdfName("123456789");
    // Read the file
    PdfReader reader = new PdfReader(src);
    int n = reader.getXrefSize();
    PdfObject object;
    PRStream stream;
    // Look for image and manipulate image stream
    for (int i = 0; i < n; i++) {
        object = reader.getPdfObject(i);
        if (object == null || !object.isStream())
            continue;
        stream = (PRStream)object;
       // if (value.equals(stream.get(key))) {
        PdfObject pdfsubtype = stream.get(PdfName.SUBTYPE);
        System.out.println(stream.type());
        if (pdfsubtype != null && pdfsubtype.toString().equals(PdfName.IMAGE.toString())) {
            PdfImageObject image = new PdfImageObject(stream);
            BufferedImage bi = image.getBufferedImage();
            if (bi == null) continue;
            int width = (int)(bi.getWidth() * FACTOR);
            int height = (int)(bi.getHeight() * FACTOR);
            BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            AffineTransform at = AffineTransform.getScaleInstance(FACTOR, FACTOR);
            Graphics2D g = img.createGraphics();
            g.drawRenderedImage(bi, at);
            ByteArrayOutputStream imgBytes = new ByteArrayOutputStream();
            ImageIO.write(img, "JPG", imgBytes);
            stream.clear();
            stream.setData(imgBytes.toByteArray(), false, PRStream.BEST_COMPRESSION);
            stream.put(PdfName.TYPE, PdfName.XOBJECT);
            stream.put(PdfName.SUBTYPE, PdfName.IMAGE);
            stream.put(key, value);
            stream.put(PdfName.FILTER, PdfName.DCTDECODE);
            stream.put(PdfName.WIDTH, new PdfNumber(width));
            stream.put(PdfName.HEIGHT, new PdfNumber(height));
            stream.put(PdfName.BITSPERCOMPONENT, new PdfNumber(8));
            stream.put(PdfName.COLORSPACE, PdfName.DEVICERGB);
        }
    }
    // Save altered PDF
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
    stamper.close();
    reader.close();
}

/**
 * Main method.
 *
 * @param    args    no arguments needed
 * @throws DocumentException 
 * @throws IOException
 */
public static void main(String[] args) throws IOException, DocumentException {
    //createPdf(RESULT);
    new ResizeImage().manipulatePdf("C:/_dev_env_/TEMP/compressPDF/TRPT_135002_1470_20131212_121423.PDF", "C:/_dev_env_/TEMP/compressPDF/compressTest.pdf");
}

}

Answer 2

Just to update the excellent answer from @Daniel, I update his code to be compatible with iText7.

package opencde.builder.compresspdf;

import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Iterator;

import javax.imageio.ImageIO;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.itextpdf.io.image.ImageDataFactory;
import com.itextpdf.kernel.pdf.PdfDictionary;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfName;
import com.itextpdf.kernel.pdf.PdfPage;
import com.itextpdf.kernel.pdf.PdfReader;
import com.itextpdf.kernel.pdf.PdfStream;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.xobject.PdfImageXObject;
import com.itextpdf.layout.element.Image;

public class ResizeImageV7 {
    
    // Logging
    private static Logger logger = LoggerFactory.getLogger(ResizeImageV7.class);

    /**
     * Manipulates a PDF file src with the file dest as result
     * 
     * @param src  the original PDF
     * @param dest the resulting PDF
     * @param resizeFactor factor to multiplicate to resize image
     * @throws IOException
     */
    public void manipulatePdf(String src, String dest,Float resizeFactor) throws IOException {
        
        //Get source pdf
        PdfDocument pdfDoc = new PdfDocument(new PdfReader(src), new PdfWriter(dest));

        // Iterate over all pages to get all images.
        for (int i = 1; i <= pdfDoc.getNumberOfPages(); i++)
        {
            PdfPage page = pdfDoc.getPage(i);
            PdfDictionary pageDict = page.getPdfObject();
            PdfDictionary resources = pageDict.getAsDictionary(PdfName.Resources);
            // Get images
            PdfDictionary xObjects = resources.getAsDictionary(PdfName.XObject);
            for (Iterator<PdfName> iter = xObjects.keySet().iterator() ; iter.hasNext(); ) {
                // Get image
                PdfName imgRef = iter.next();
                PdfStream stream = xObjects.getAsStream(imgRef);
                PdfImageXObject image = new PdfImageXObject(stream);
                BufferedImage bi = image.getBufferedImage();
                if (bi == null)
                    continue;
                
                // Create new image
                int width = (int) (bi.getWidth() * resizeFactor);
                int height = (int) (bi.getHeight() * resizeFactor);
                BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
                AffineTransform at = AffineTransform.getScaleInstance(resizeFactor, resizeFactor);
                Graphics2D g = img.createGraphics();
                g.drawRenderedImage(bi, at);
                ByteArrayOutputStream imgBytes = new ByteArrayOutputStream();
                
                // Write new image
                ImageIO.write(img, "JPG", imgBytes);
                Image imgNew =new Image(ImageDataFactory.create(imgBytes.toByteArray()));
                
                // Replace the original image with the resized image
                xObjects.put(imgRef, imgNew.getXObject().getPdfObject());
            }          
        }
        
        pdfDoc.close();
    }

    /**
     * Main method.
     *
     * @param src  the original PDF
     * @param dest the resulting PDF
     * @param resizeFactor factor to multiplicate to resize image
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
        //Get input parametres
        if (args.length<3 ) {
            System.out.println("Source PDF, Destination PDF and Resize Factor must be provided as parametres");
        } else {
            String sourcePDF=args[0];
            String destPDF=args[1];
            Float resizeFactor=Float.valueOf(new String(args[2]));
            logger.info("Inovking Resize with args, source:" + sourcePDF
                    + " destination:" + destPDF 
                    + " factor:" + resizeFactor);
            //Call method to resize images
            new ResizeImageV7().manipulatePdf(sourcePDF,destPDF,resizeFactor);
            logger.info("PDF resized");
        }
    }

}