Slow OCR with tesseract 4.00alpha

[innir]

Hi,

as tesseract 4.00-dev was uploaded to Debian (why is another question), gImageReader was rebuild against it. Now the recognition speed is about 10 times (!) lower than with tesseract 3.05. Using the command line tesseract does not show this slow speed.
Do you have any idea what goes wrong here? I'll happily test patches :-)

Best,
Philip

[manisandro]

Uh no idea, there are actually only three calls to tesseract really, see [1], so I'm not doing anything terribly fancy client side. Might be worth asking upstream.

[1] https://github.com/manisandro/gImageReader/blob/master/gtk/src/Recognizer.cc#L490

[innir]

Hm strange, the difference between command line tesseract and gImageReader is even bigger 2.4s vs. 1:30 min! Both use all available CPU cores. Yes, asking upstream seems reasonable. Probably someone should double check first?

[manisandro]

Are you testing in plain text or hOCR mode or both? Any difference between the two?

[innir]

Plain text before, now hOCR: tesseract: 2.7s vs. gImageReader 1:11 min

[manisandro]

:\ That's pretty disasterous

[manisandro]

Can you try playing with the page segmentation modes in the menu of the recognition button?

[innir]

No changes in speed, but option two (from top) gives a crash: https://pastebin.com/Xwxqxbes while tesseract --psm 1 ... doesn't crash

On the console:

Error: Illegal Parameter specification!
"Fatal error encountered!" == NULL:Error:Assert failed:in file globaloc.cpp, line 75

[manisandro]

I'll build the latest tesseract git and do some testing.

[innir]

The main difference I see is that tesseract 4.00 uses multiple threads while 3.04 does not.
I can also confirm that gImagerader 3.2.0 build against tessarect 3.04 does not show this speed decrease. command line and gImageReader are both ~12s (different computer).

[manisandro]

There are indeed reports of openmp causing slowdowns, i.e. tesseract-ocr/tesseract#961

[innir]

Well, but that doesn't explains why tesseract 4.00. with openmp is fast for me

[manisandro]

Uhm, so testing latest gimagereader git and tesseract-4.00.gitbc668da, recognizing a 10 page document in hOCR mode takes 46 seconds, while 3.05.00 takes 38 seconds. So not that much of a slowdown. Tesseract compiled without passing any particular options to configure, which resulted in an OpenMP-enabled but OpenCL-disabled build. But I only see 2/8 cores fully used.

[innir]

Using upstreams tesseract without modification didn't change anything, I used gImageReader 3.2.3 though, it uses all my 4 cores - using the gtk version

[manisandro]

Does it depend on the language used? Any particularly complex document? Can you try with latest gimagereader-git?

[innir]

No, language doesn't change anything. The test image is here: https://imgur.com/a/dkpHz - not complex at all.
I'll try to build gimagereader-git