How to fix the orientation of a PDF page in order to scale it?

Tags: page sizepage orientationscale contentiText 5

I need to scale down the pages of an existing PDF document. This works fine if the pages aren't rotated, but I don't succeed in rotating pages correctly, for instance if they have a rotation of 270 degrees:

for(int i=1; i<=reader.getNumberOfPages(); i++){
    int rotation = reader.getPageRotation(i);
    float pageWidth = reader.getPageSizeWithRotation(i).getWidth();
    float pageHeight = reader.getPageSizeWithRotation(i).getHeight();
    doc.newPage();
    PdfImportedPage page = writer.getImportedPage(reader, i);
    if (rotation == 0) {
        cb.addTemplate(page, 1f, 0, 0, scaleHeight, x, y);
    } else if (rotation == 90) {
        cb.addTemplate(page, 0, -1f, 1f, 0, 0, pageHeight);
    } else if (rotation == 180) {
        cb.addTemplate(page, 1f, 0, 0, -1f, pageWidth, pageHeight);
    } else if (rotation == 270) {
        cb.addTemplate(page, 0, -1f, 1f, 0, 0, pageHeight);
    }
}
I have two questions:

  1. How do I properly rotate the page contents?
  2. How can I scale the rotated contents correctly?

Posted on StackOverflow on Mar 19, 2014 by user3854377

Please take a look at the ScaleDown example that can be used to scale down pages, keeping the original orientation.

This example uses a page event named it ScaleEvent:

public class ScaleEvent extends PdfPageEventHelper {
    protected float scale = 1;
    protected PdfDictionary pageDict;
    public ScaleEvent(float scale) {
        this.scale = scale;
    }
    public void setPageDict(PdfDictionary pageDict) {
        this.pageDict = pageDict;
    }
    @Override
    public void onStartPage(PdfWriter writer, Document document) {
        writer.addPageDictEntry(PdfName.ROTATE, pageDict.getAsNumber(PdfName.ROTATE));
        writer.addPageDictEntry(PdfName.MEDIABOX, scaleDown(pageDict.getAsArray(PdfName.MEDIABOX), scale));
        writer.addPageDictEntry(PdfName.CROPBOX, scaleDown(pageDict.getAsArray(PdfName.CROPBOX), scale));
    }
}

When you create the event, you pass a value scale that will define the scale factor. I apply the scale to the width and the height, feel free to adapt it if you only want to scale the height or the width only.

The information about page size and rotation is stored in the page dictionary. Obviously the ScaleEvent needs the values of the original document, and that why we'll pass a pageDict for every page we copy.

Every time a new page is created, we will copy/replace:

  • the /Rotate value. Remove this line if you want to remove the rotation,

  • the /MediaBox value. This defines the full size of the page.

  • the /CropBox value. This defines the visible size of the page.

As we want to scale the page, we use the following scaleDown() method:

public PdfArray scaleDown(PdfArray original, float scale) {
    if (original == null)
        return null;
    float width = original.getAsNumber(2).floatValue()
            - original.getAsNumber(0).floatValue();
    float height = original.getAsNumber(3).floatValue()
            - original.getAsNumber(1).floatValue();
    return new PdfRectangle(width * scale, height * scale);
}

Suppose that I want to reduce the page width and height to 50% of the original width and height, then I create the event like this:

PdfReader reader = new PdfReader(src);
float scale = 0.5f;
ScaleEvent event = new ScaleEvent(scale);
event.setPageDict(reader.getPageN(1));

I can define a Document with any page size I want as the size will be changed in the ScaleEvent anyway. For this to work I need to declare the event to the PdfWriter instance before opening the document:

Document document = new Document();
PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(dest));
writer.setPageEvent(event);
document.open();

Now it's only a matter of looping over the pages:

int n = reader.getNumberOfPages();
Image page;
for (int p = 1; p <= n; p++) {
    page = Image.getInstance(writer.getImportedPage(reader, p));
    page.setAbsolutePosition(0, 0);
    page.scalePercent(scale * 100);
    document.add(page);
    if (p < n) {
        event.setPageDict(reader.getPageN(p + 1));
    }
    document.newPage();
}
document.close();

I am wrapping the imported page inside an Image because I personally think that the methods available for the Image class are easier to use than defining the parameters of the addTemplate() method. If you want to use addTemplate() instead of Image, feel free to do so; the result will be identical (contrary to what you wrote in a comment, wrapping a page inside an image will not cause any loss of "resolution" as all the text remains available as vector data).

Note that I update the pageDict for every new page.

This code takes the file orientations.pdf measuring 8.26 by 11.69 in and transforms it into the file scaled_down.pdf measuring 4.13 by 5.85 in.