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Is it possible to run mutool.exe draw using several threads to increase PDF to Image conversion speed? The command help list says something about -B and -T parameters, but I do not understand what maximum band_height does? What values should I set for -B?

-B -    maximum band_height (pXm, pcl, pclm, ocr.pdf, ps, psd and png output only)
-T -    number of threads to use for rendering (banded mode only)

Executing mutool with -B 100 -T 6 slightly increased conversion speed by 10% but not so much, the CPU usage spiked from 6% to 11%, but why not 60%?

mutool.exe draw -r 300 -B 100 -T 6 -o "C:\test%d.png" "C:\test-large.pdf"
Tomas
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1 Answers1

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Every system and PDF is different but lets use a single page without text for timings in my system.

I know this file is complex but not too unusual since without text, other objects behave as text would, without the complexity of font look-up etc. so rendering time is generally fairly similar for a given run.

Lets start with a low resolution since I know the file well enough to have found it fail due to Malloc in this machine around 300dpi.

mutool draw -Dst -r 50 -o complex.png complex.pdf
page complex.pdf 1 1691ms
total 1691ms (0ms layout) / 1 pages for an average of 1691ms

We can see using a PDF screen viewer timings, that's good as the screen render (which is darn fast at 2 seconds for that 1 PDF page) is about 96dpi

LoadDocument: 5.47 ms, 1 pages  
Slow rendering: 2035.27 ms, page: 1

mutool draw -Dst -r 100 -o complex.png complex.pdf
page complex.pdf 1 3299ms
total 3299ms (0ms layout) / 1 pages for an average of 3299ms

mutool draw -Dst -r 200 -o complex.png complex.pdf
page complex.pdf 1 7959ms
total 7959ms (0ms layout) / 1 pages for an average of 7959ms

mutool draw -Dst -r 400 -o complex.png complex.pdf
page complex.pdf 1error: malloc of 2220451350 bytes failed
error: cannot draw 'complex.pdf'

So this is when "Banding" is required to avoid memory issues since my target is 400 dpi output.

You may see I used -D above so I need to remove that for threads, cannot use multiple threads without using display list. Lets start small since too large bands or too many threads can also malloc error.

mutool draw -st -B 32 -T 2 -r 400 -o complex.png complex.pdf
page complex.pdf 1 14111ms
total 14111ms (0ms layout) / 1 pages for an average of 14111ms

14 seconds for this file is not a bad result based on the progressive timings above, but perhaps on this 8 thread device I could do better? Lets try bigger bands and more threads.

mutool draw -st -B 32 -T 3 -r 400 -o complex.png complex.pdf
page complex.pdf 1 12726ms
total 12726ms (0ms layout) / 1 pages for an average of 12726ms

mutool draw -st -B 256 -T 3 -r 400 -o complex.png complex.pdf
page complex.pdf 1 12234ms
total 12234ms (0ms layout) / 1 pages for an average of 12234ms

mutool draw -st -B 256 -T 6 -r 400 -o complex.png complex.pdf
page complex.pdf 1 12258ms
total 12258ms (0ms layout) / 1 pages for an average of 12258ms

So increasing threads up to 3 helps and upping the Band size helps, but 6 threads is no better. So is there another tweak we can consider, and playing around with many runs the best I got on this kit/configuration was 12 seconds.

mutool draw -Pst -B 128 -T 4 -r 400 -o complex.png complex.pdf
page complex.pdf 1 1111ms (interpretation) 10968ms (rendering) 12079ms (total)
K J
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