Ghostscript to compress a batch of PDFs

Question

I have no experience of programming.

My PDFs won't display images on the iPad in PDFExpert or GoodNotes as the images are in JPEG2000, from what I could find on the internet.

These are large PDFs, upto 1500-2000 pages with images. One of these was an 80MB or so file. I tried printing it with Foxit to convert the images to JPG from JPEG2000 but the file size jumped to 800MB...plus it's taking too long.

I stumbled upon Ghostscript, but I have NO clue how to use the command line interface.

I am very short on time. Pretty much need a step by step guide for a small script that converts all my PDFs in one go.

Very sorry about my inexperience and helplessness. Can someone spoon-feed me the steps for this?

EDIT: I want to switch the JPEG2000 to any other format that produces less of an increase in file size and causes a minimal loss in quality (within reason). I have no clue how to use Ghostscript. I basically want to change the compression on the images to something that will display correctly on the iPad while maintaining the quality of the rest of the text, as well as the embedded bookmarks.

I'll repeat that I have NO experience with command line...I don't even know how to point GS to the folder my PDFs are in...

Answer 1

You haven't really said what it is you want. 'Convert' PDFs how exactly ?

Note that switching from JPX (JPEG2000) to JPEG will result in a quality loss, because the image data will be quantised (with a different quantisation scheme to JPX) by the JPEG encoder. You can use a lossless compression scheme instead, but then you won't get the same kind of compression. You won't get the same compression ratio as JPX anyway no matter what you use, the result will be larger.

A simple Ghostscript command would be:

gs -sDEVICE=pdfwrite -o out.pdf in.pdf

Because JPEG2000 encoding is (or at least, was) patent encumbered, the pdfwrite device doesn't write images as JPX< by default it will write them several times with different compression schemes, and then use the one that gives the best compression (practically always JPEG).

Getting better results will require more a complex command line, but you'll also have to be more explicit about what exactly you want to achieve, and what the perceived problem with the simplistic command line is.

[EDIT]

Well, giving help on executing a command line is a bit off-topic for Stack Overflow, this is supposed to be a site for software developers :-)

Without knowing what operating system you are using its hard to give you detailed instructions, I also have no idea what an iPad uses, I don't generally use Apple devices and my only experience is with Macs.

Presumably you know where (the directory) you installed Ghostscript. Either open a command shell there and type the command ./gs or execute the command by giving the full path, such as :

/usr/bin/gs

I thought the arguments on the command line were self-explanatory, but....

The -sDEVICE=pdfwrite switch tells Ghostscript to use the pdfwrite device, as you might guess from the name, that device writes PDF files as its output.

The -o switch is the name (and full path if required) of the output file.

The final argument is the name (and again, full path if its not in the current directory) of the input file.

So a command might look like:

/usr/bin/gs -sDEVICE=pdfwrite -o /home/me/output.pdf /home/me/input.pdf

Or if Ghostscript and the input file are in the same directory:

./gs -sDEVICE=pdfwrite -o out.pdf input.pdf