iTextSharp change outcome quality / compression like PDF24Creator

问题

I was wondering if I can compress/Change the Quality of my outcoming pdf-file with iTextSharp and C# like I can do with Adobe Acrobat Pro or PDF24Creator.

Using the PDF24Creator I can open the pdf, save the file again and set the "Quality of the PDF" to "Low Quality" and my file size decreases from 88,6MB to 12,5MB while the Quality is still good enough.

I am already using the

    writer = new PdfCopy(doc, fs);
    writer.SetPdfVersion(PdfCopy.PDF_VERSION_1_7);
    writer.CompressionLevel = PdfStream.BEST_COMPRESSION;
    writer.SetFullCompression();

which decreases the file size from about 92MB to 88MB.

Alternatively: Can I run the pdf24 Program through my C# code using command line arguments or starting Parameters? Something like that:

pdf24Creator.exe -save -Quality:low -inputfile -outputfile

Thanks for your help (Bruno)!

回答1:

Short answer: no.

Long answer: yes but you must do a lot of the work yourself.

If you read the third and fourth paragraphs here you'll hopefully get a better understanding of what "compression" actually means from a PDF perspective.

Programs like Adobe Acrobat and PDF24 Creator allow you to reduce the size of a file by destroying the data within the PDF. When you select a low quality setting one of the most common changes these programs make is to actually extract all of the images, reduce their quality and replace the original files in the PDF. So a JPEG originally saved without any compression might be knocked down to 60% quality. And just to be clear, that 60% is non-reversible, it isn't zipping the file, it is literally destroying the data in order to save space.

Another setting is to reduce the effective DPI of an image. A 500 pixel wide image placed into a 2 inch wide box is effectively 250 DPI. These programs will extract the image, reduce the image to maybe 96 or 72 DPI which means the 500 pixel image be reduced to 192 or 144 pixels in width and replace the original file in the PDF. Once again, this is a destructive non-reversible change.

(And by destructive non-reversible, you still probably have the original file, I just want to be clear that this isn't true "compression" like ZIP.)

However, if you really want to do it you can look at code like this which shows how you can use iText to perform the extraction and re-insertion of images. It is 100% up to you, however, to change the images because iText won't make destructive changes to your data (and that's a good thing I'd say!)

来源：https://stackoverflow.com/questions/28715068/itextsharp-change-outcome-quality-compression-like-pdf24creator

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