Tagger does not decode Datamatrix codes

Datamatrix codes can be decoded using the libdmtx library. Initial attempts to utilise this were unsuccessful. Having experimented with the settings I have determined that they can vary between codes. The command I used was:

dmtxread -q20 -S2 filename.png

-q specifying the angle at which the code can be presented off square and -S being the multiplier to reduce the size of the image by. It appears that some images decode with -S2 and others with -S3. I have no idea if this setting may vary further.

One of the codes I used initially decoded incorrectly, so it seems some thought would need to be given to how you determine the decode is correct and also about how to probe the multiple variations of settings. A successful read seems to be very quick, a failure will continue trying for considerably longer.