iTextsharp - PDF file size after inserting image.

Question

I'm currently converting some legacy code to create PDF files using iTextSharp. We're creating a largish PDF file that contains a number of images, which I'm inserting like so:

Document doc = new Document(PageSize.A4, 50, 50, 25, 25);
PdfWriter writer = PdfWriter.GetInstance(doc, myStream);

writer.SetFullCompression();

doc.Open();

Image frontCover = iTextSharp.text.Image.GetInstance(@"C:\MyImage.png");

//Scale down from a 96 dpi image to standard itextsharp 72 dpi
frontCover.ScalePercent(75f);

frontCover.SetAbsolutePosition(0, 0);

doc.Add(frontCover);

doc.Close();

Inserting an image (20.8 KB png file) seems to increase the PDF file size by nearly 100 KB.

Is there a way of compressing the image before entry (bearing in mind that this needs to be of reasonable print quality), or of further compressing the entire PDF? Am I even performing any compression in the above example?

Answer 1

It seems that PDF requires the png to be transcoded to something else, jpeg, most probably.

see here: http://forums.adobe.com/message/2952201

The only thing I can think of is to convert png to smallest jpeg first, including scaling down 75%, then importing that file without scaling.

Answer 2

The answer appears to have been that you need to set an appropriate version of the PDF spec to target and then set the compression as follows:

PdfWriter writer = PdfWriter.GetInstance(doc, ms);
PdfContentByte contentPlacer;

writer.SetPdfVersion(PdfWriter.PDF_VERSION_1_5);

writer.CompressionLevel = PdfStream.BEST_COMPRESSION;

This has brought my file size down considerably. I also found that PNG's were giving me the best results as regards to final size of document.