David Moore wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Michael Droettboom wrote: >> Jesper Larsen wrote: >>> Hi Matplotlib users, >>> >>> I have an application which produces PNG files using the AGG backend. >>> When I profile the application I can see that much of the cpu time is >>> spent in the method write_png called by print_figure in backend_agg.py. >> I have seen this myself. Keep in mind that timing includes a lot of >> disk I/O, so if your images are particularly large, or you're saving to >> a network or external disk, or if another process steps in at that >> moment and wants to read/write to the disk, that could be the >> bottleneck, more so than just the CPU time spent doing the PNG >> compression. On any reasonably modern PC, I suspect that's the case. >> >>> Does anyone know which backend is the best for producing fast good >>> quality PNG files (with fast being as important as good quality)? >> They should all be approximately the same wrt actually writing out the >> file -- they're all using libpng either directly or indirectly. It also >> means there's not much that matplotlib can do to improve its >> performance, short of submitting patches to libpng -- but I suspect >> there isn't a lot of long-hanging fruit left to improve in such a >> widely-used library. >> >>> In another thread I read that antialiasing could be disabled for better >>> performance. I tried doing that in each call to contourf and it resulted >>> in a performance improvement. Does anyone have other performance tips >>> with regard to PNG files? >> Saving to a Python file-like object (if you're doing that) is slower >> than saving directly to a file path. > > This seems to contradict your previous assertion that the bottleneck is likely > to be disk I/O - if you're saving to a Python file-like object, there's no > disk > I/O. Why is this slower?
All things being equal -- if the Python file-like object is saving to an on-disk file -- the Python file-like object will be slower. Sometimes people do this if the want another layer of abstraction (e.g. saving to a gzip file) or to be more general. What I mean is that: savefig(open(filename)) is slower than savefig(filename) because the latter makes a Python function call to save each block of data. Mike -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
