Skipping OCR processing based on logical `mets:structMap`

[mikegerber]

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From my and @bertsky's discussion at https://github.com/qurator-spk/eynollah/issues/67:

Yes, it should be possible to skip pages marked as certain types in the logical structmap – not just in any one processor, but as a general mechanism for workflows in OCR-D.

For the concrete set of supported page types, we should stick to DFG Strukturdatenset, which is strangely missing colour_checker.

100% agree! Should we take this to an OCR-D core or spec issue? I have some additional thoughts to discuss (like: What happens with skipped pages in the output?)

• It should be possible to skip pages with structMap types like spine or colour_checker. (@maria-federbusch supplied us at SBB with a list, I'll copy it in here.)
• What should happen with skipped pages in the output? Empty PAGE or just omitted? What are the drawbacks of each approach?

[mikegerber]

For the concrete set of supported page types, we should stick to DFG Strukturdatenset, which is strangely missing colour_checker.

That's a custom type used at SBB, invented by @maria-federbusch.

[bertsky]

missing colour_checker.

That's a custom type used at SBB, invented by @maria-federbusch.

I was surprised to see it in mets-mods2tei, but not in kitodo.presentation or dfg-viewer. Maybe you want to open a PR for that?

• What should happen with skipped pages in the output? Empty PAGE or just omitted? What are the drawbacks of each approach?

again, see previous discussion

[bertsky]

One might think of an additional CLI option, say -G, --page-type, matching mets:structMap[@TYPE="LOGICAL"]//mets:div/@TYPE of pages in that range of the mets:structLink (if any), perhaps even with //-prefixed regexes.

But practically, there are too many positive cases to include, and only a few fixed negative ones: cover_front, cover_back, binding, spine, privileges, note.

So maybe we should just recommend ignoring all physical pages belonging to these page ranges in the implementation (and implement that behaviour for all Pythonic and bashlib processors in core)?

[M3ssman]

Additionally, I do use the information from physical containers. We have often custom labeled containers alike Leerseite or Colorchecker ( :slightly_smiling_face: ) on this area.

[M3ssman]

If Image has been skipped due logical / physical mismatch, there's no FULLTEXT existing, and nothing linked in the physical container, too.

[bertsky]

@M3ssman on the OCR-D Forum you said that you have a workflow to do page selection based on logical structmap externally (independent of OCR-D) – could you elaborate here?

[M3ssman]

It analyzes the METS and filters images by defined labels like the logical ones from DFG-structset like cover_front and cover_back and custom physical annotations like Colorchecker , Leerseite, Illustration and so on. For the later you are required to have this information present, for example it has been enriched by your digitization colleagues. For rather small prints (<100 pages) this means saving 10% or more.

This relies on the fact, that each page is processed afterwards in separate ocrd-workspaces. Only for images which do not match the blacklisted label are those workspaces created. Afterwards only the existing OCR is enriched as FULLTEXT, leaving some pages empty. I did not experienced any drawbacks of this approach in the last half year.

Works also when creating new PDFs from resulting ALTO-Data using derivans tool.

To enhance this for complete ocrd-workspaces, one could probably combine this even with lazy-loading to don't download these images locally.

[bertsky]

ok, so in principle it's clear that if you use the split recipe (dividing up the METS into single-page workspaces to be processed in parallel), then it is easy to filter by logical page type. (Still, I was hoping for some concrete technical details.)

Getting back to the question how to do this with OCR-D: @kba, can you please weigh in (esp. whether we should do this with positive/negative filters on a new CLI option, or rather by implicit filtering in core, perhaps even configurable...)?