Reduce size of iText generated PDF including time series bar chart

Question

Adding a time series bar chart for a large time span in PDF results in large file size like 50 MB or more depending on the data points. Here are the code samples:

Adding chart to PDF

Document document = new Document();
PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(RESULT));
document.open();
PdfContentByte cb = writer.getDirectContent();
float width = PageSize.A4.getWidth();
float height = PageSize.A4.getHeight() / 2;

PdfTemplate bar = cb.createTemplate(width, height);
Graphics2D g2d2 = new PdfGraphics2D(bar, width, height);
Rectangle2D r2d2 = new Rectangle2D.Double(0, 0, width, height);
getBarChart().draw(g2d2, r2d2);
g2d2.dispose();
cb.addTemplate(bar, 0, 0);
document.close();

Creating chart

JFreeChart getBarChart() {
    TimeSeries series = new TimeSeries("Data");
    
    GregorianCalendar cal = new GregorianCalendar();
    for (int i=0; i<365*24; i++) {
        cal.add(Calendar.HOUR, 1);
        series.addOrUpdate(new Millisecond(cal.getTime()), Math.random());
    }
    
    XYPlot plot = new XYPlot();
    plot.setDataset(new XYBarDataset(new TimeSeriesCollection(series), 10));
    plot.setRenderer(new XYBarRenderer());
    plot.setRangeAxis(new NumberAxis());
    plot.setDomainAxis(new DateAxis());

    return new JFreeChart(plot);
}

How can I reduce the file size?

Using itextpdf-5.4.4 and jfreechart-1.0.15.

Answer 1

While inspecting the PDF provided by the OP, it quickly becomes apparent that it is full of Pattern definitions and the like used for drawing pretty bars. To reduce the PDF size, therefore, simplifying the bar design is the way to go.

In the case at hand this can be done by setting a different default bar painter (using XYBarRenderer.setDefaultBarPainter()). The initial value of that attribute is a GradientXYBarPainter, but using gradients for so small bars makes the number of required drawing operations and operators explode while only making a difference at a gigantic zoom level, if at all.

As already worked out in the comments to the question, using the StandardXYBarPainter instead solves the size issues.