Re: [libdmtx-open_discussion] Using libdmtx on constrained ARM device (i.e. Nokia N900)

[Mike L. <mi...@dr...>]

Hi Simon,

Thanks for your message, and for mbarcode!

Datamatrix is comparatively slow on the N900 (compared with QR decoding for
> example), which is doubtless partly because QR has nice big recognition
> symbols which make alignment of the barcode far easier, but I also wanted to
> check and see what options people would recommend using to improve
> performance?


That's a good question. When left untuned, libdmtx can bog down under
certain image conditions. There are plans in the works to overhaul the
relevant code, but for now the best thing is to identify and correct the
problem through tuning parameters. Is it possible for you to send some
sample images, and problematic ones in particular? We might be able to help
out.

I don't see any reason that we can't ultimately be every bit as fast as QR
Code. :)

The data I'm feeding to the decoder is 320 x 240 pixels Y800 (though 640 x
> 480 is also available if that would improve things) and currently I simply
> set the decoder timeout. I see that there are lots of options (e.g.
> http://git.tal.org/gitweb.cgi?p=gst-dmtx.git;a=blob;f=gst-dmtx-test-pipe.sh;
> h=72951bdd9326fcee47475da61a5808e06aca4a51;hb=HEAD), what would people
> recommend and most importantly, is there a list describing these anywhere
> (e.g. what does "skip" do and does "scale=2" shrink the image by a factor of
> 2?)


I recommend checking out the page at
http://libdmtx.wikidot.com/helpful-tipsfor a brief description of some
tuning parameters as they relate to libdmtx
itself (i.e., not necessarily the Gstreamer module). You can also refer to
the man page for dmtxread (availble online at
http://libdmtx.org/display.php?text=dmtxread.1)

I briefly looked at the gst-dmtx code and it appears that "skip" is related
to frame rate (as in "only pay attention to every 30th frame in this
stream), whereas "scale=2" does in fact relate to the "shrink" option in
libdmtx "proper". If you are already working with small-ish images (320x240)
then the "scale=2" option probably won't help your performance, and in fact
will probably hurt the scan reliability.

I hope this helps. I'm looking forward to seeing some example images so we
can improve the tuning.

Mike

-- 
Mike Laughton
Chief Software Architect
Dragonfly Logic, Inc.
612.845.3339 (m)