Any tips for speeding up GhostScript?

I was crunching a ~300 page PDF on a core i7 and found that adding the following options provided a significant speedup:

                            %-> comments to the right 
-dNumRenderingThreads=8     % increasing up to 64 didn't make much difference
-dBandHeight=100            % didn't matter much
-dBandBufferSpace=500000000 % (500MB)
-sBandListStorage=memory    % may or may not need to be set when gs is compiled
-dBufferSpace=1000000000    % (1GB)

The -c 1000000000 setnvmthreshold -f thing didn't make much difference for me, FWIW.

If you are on a multicore system, make it use multiple CPU cores with:

-dNumRenderingThreads=<number of cpus>

Let it use up to 30mb of RAM:

-c "30000000 setvmthreshold"

Try disabling the garbage collector:

-dNOGC

Fore more details, see Improving Performance section from Ghoscript docs.

You don't say what CPU and what amount of RAM your computer is equipped with.

Your situation is this:

• A scanned document as PDF, sized about 500 kB per page on avarage. That means each page basically is a picture, using the scan resolution (at least 200 dpi, maybe even 600 dpi).
• You are re-distilling it with Ghostscript, using -dPDFSETTINGS=/screen. This setting will do quite a few things to make the file size smaller. Amongst the most important are:
  1. Re-sample all (color or grayscale) images to 72dpi
  2. Convert all colors to sRGB

Both these operations can quite "expensive" in terms of CPU and/or RAM usage.

BTW, your setting of -dCompatibilityLevel=1.3 is not required; it's already implicitely set by -dPDFSETTINGS=/screen already.

Try this:

gswin32.exe ^
 -o output.pdf ^
 -sDEVICE=pdfwrite ^
 -dPDFSETTINGS=/screen ^
 -dNumRenderingThreads=2 ^
 -dMaxPatternBitmap=1000000 ^
 -c "60000000 setvmthreshold" ^
 -f input.pdf

Also, if you are on a 64bit system, try to install the most recent 32bit Ghostscript version (9.00). It performs better than the 64bit version.

Let me tell you that downsampling a 600dpi scanned page image to 72dpi usually does not take 23 seconds for me, but less than 1.