ghostscript - Dramatic speed difference between PDF to PNG vs. PDF to JPEG -


using pdftocairo, on xeon e5-2630 (2.3ghz) centos 6.3 machine, poppler 0.24, cairo 1.12, libpng 1.2.49, openjpeg 1.3.10 (both centos default), tested converting 37 page pdf convert jpeg , png. ran pdftocairo no special options (so no alpha channel png, density @ 150ppi). speed difference enormous:

pdf png:

real    0m16.858s user    0m16.552s sys     0m0.154s

that works out 0.43s per page.

pdf jpeg:

real    0m1.762s user    0m1.666s sys     0m0.081s

which is, well, 10 times faster.

now tested using gs convert, same options, , results are:

pdf png:

real    0m16.500s user    0m16.223s sys     0m0.093s

almost identical in speed poppler, strangely.

pdf jpeg:

real    0m7.468s user    0m7.304s sys     0m0.079s

much slower poppler, somehow, included comparison.

why converting png slower? need convert them pngs, there wrong libpng setups? it's curious gs slower when converting jpegs identical pngs.

png compression speed governed zlib compression level , zlib strategy. trade off compression speed compression ratio. compression speed affected lesser degree png filter method, "none" being fastest , "paeth" being slowest. slower commonly-used "adaptive filtering" computes figure of merit each of 5 filter types , selects best each scanline.


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