good accuracy but too slow, how to improve Tesseract speed

[ychtioui]

I integrated Tesseract C/C++, version 3.x, to read English OCR on images.

It’s working pretty good, but very slow. It takes close to 1000ms (1 second) to read the attached image (00060.jpg) on my quad-core laptop.

I’m not using the Cube engine, and I’m feeding only binary images to the OCR reader.

Any way to make it faster. Any ideas on how to make Tesseract read faster?
thanks

[stweil]

You can already run 4 parallel instances of Tesseract on your quad core, then it will read 4 images in about the same time. Introducing multi threading would not help to reduce the time needed for an OCR of many images. I am working on a project where OCR with Tesseract would take nearly 7 years on a single core, but luckily I can try to get many computers and use their cores, so the time can be reduced to a few days.
Using compiler settings which are optimized for your CPU helps to gain a few percent, but I am afraid that for a larger gain different algorithms in Tesseract and its libraries would be needed.

[ychtioui]

Besides the OCR, we have other things that need to run on the other cores.
I believe, the main issue that's slowing down Tesseract is the way memory is managed.
Too many memory allocations (new function) and releases (delete or delete [] functions) do slow down the reader.
In the past, I did use a different OCR engine, and it was allocating up-front large buffers to store all the needed data (large buffer of blobs, a large buffer of lines, a large buffer of words and their corresponding data), the buffers were just being indexed as we were reading the data from an image. The large buffers were allocated only once upon ocr engine initialization and release only once upon ocr engine shutdown. This memory management scheme was very efficient computational-time-wise.
Are there any settings for Tesseract that are known to be computationally intensive?
any tricks to speed up Tesseract?

[tfmorris]

What evidence is your memory management speculation based on?

[ychtioui]

I'm not speculating anything. The reality is that TesseRact takes more than 3 seconds to read the above image that I initially attached (I use VS2010). When I use the console test application that comes with the TesseRact, it takes about the same time (more than 3 seconds).

Anyone would speculate a lot in 3 seconds

I have more than 20 years in machine vision. I used several OCR engines in the past. Actually I have one -in house- that reads the same image in less than 100ms, but our engine is designed more for reading a single line of text (i.e. it returns a single line of text).

TesseRact database is not that large. Most of the techniques used by TesseRact are quite standard in the OCR-area (page layout, line extraction, possible character extraction, word forming, and then several phases of classification). However, the TesseRact manages very badly memory usage. why? it takes more than 3 seconds to read a typical texted-image.

please if you're not bringing any meaningful ideas to my posting, just spare me your comment.

[stweil]

@ychtioui, as you have spent many years in machine vision, you know quite well that there are lots of ways why programs can be slow. Memory management is just one of them. Even with a lot of experience, I'd start running performance analyzers to investigate performance issues. Of course I can guess what might be possible reasons and try to improve the software based on that guesses, but improvements based on evidence (like the result of a performance analysis) are more efficient. Don't you think so, too? Do you have a chance to run a performance analysis?

[zdenop]

You can try to use 3.02 version if you need only English. AFAIR it was
singnificantly faster on my (old) computer.

Zdenko

On Thu, Mar 10, 2016 at 4:35 PM, younes notifications@github.com wrote:

I integrated Tesseract C/C++, version 3.x, to read English OCR on images.

It’s working pretty good, but very slow. It takes close to 1000ms (1
second) to read the attached image (00060.jpg) on my quad-core laptop.

I’m not using the Cube engine, and I’m feeding only binary images to the
OCR reader.

Any way to make it faster. Any ideas on how to make Tesseract read faster?
thanks
[image: 00060]
https://cloud.githubusercontent.com/assets/9968625/13674495/ac261db4-e6ab-11e5-9b4a-ad91d5b4ff87.jpg

—
Reply to this email directly or view it on GitHub
#263.

[ychtioui]

I'm running version 3.02
I'm going through different sections of the reader, and checking which section is taking the most time.

is it typical to read images (such as mine attached above) in a few seconds?

thanks for your comments.

[amitdo]

... 3.02 version ... AFAIR it was significantly faster on my (old) computer.

3.02 3.02.02 is compiled with '-O3' by default.
https://github.com/tesseract-ocr/tesseract/blob/3.02.02/configure.ac#L161

3.03 and 3.04 are compiled with '-O2' by default.
https://github.com/tesseract-ocr/tesseract/blob/3.03-rc1/configure.ac#L201
https://github.com/tesseract-ocr/tesseract/blob/3.04.01/configure.ac#L300

2.04 and 3.01 are compiled with '-O0' '-O2' by default.
https://github.com/tesseract-ocr/tesseract/blob/2.04/configure.ac
https://github.com/tesseract-ocr/tesseract/blob/3.01/configure.ac
The 'configure.ac' script in these versions does not explicitly set the '-O' level, so autotools will use '-O0' '-O2' as default.

[ychtioui]

thanks amitdo.
I'm using 3.02 but the C/C++ version of Tesseract.
I couldn't find the setting -O3 in the source files. where is it?

[amitdo]

What I linked to was actually 3.02.02

I think this is 3.02:
https://github.com/tesseract-ocr/tesseract/blob/d581ab7e12a2fac4a73ac0af4ce7ec522b8f3e42/configure.ac

You are right. It does not contain any '-On' flag, so the compiler will use '-O0', which is not good for speed. so if you are using autotools to build Tesseract it will instruct the compiler to use '-O2'.

[amitdo]

I assume you are using Tesseract on Linux / FreeBSD / Mac. On Windows + MS Visual C++ the configure.ac file is irrelevant.

[Shreeshrii]

@ychtioui said in a post above "I use VS2010" so using Windows.

[amitdo]

Thanks Shree.

I don't know which optimization level is used for Visual C++.

[ychtioui]

I use vs2010 on a Windows 7 pc.
Project settings or building options won't change much the read speed.
Tesseract was designed in research labs. Most of the key sections of the reader are speed-don't-care.
I used some performance tools to analyze where most of the computation time is spent.
In the page layout section, the blob analyzer does a lot of new/delete. This is very time consuming. The attached image above has more than 3600 blobs. Besides a number of processings are done on each blob (distance transform, finding the enclosing rectangle, measuring blob parameters, etc.). The allocations (new) and the release (delete) of all these blobs is very time consuming.
If we use a global array (allocate upfront) of blobs (exactly object BLOBNBOX) and whenever we need a blob, just get one index from the array. The array will be released once when we shut down the engine.
I used this concept in another single line ocr reader and it's super fast.

[zdenop]

VS2010 use optimization flag /O2 (Maximize speed) - other flags are set to default.
In past in forum there were warnings against using compiler optimization flag as they affect also OCR results. This is reason why there are standard optimization flags (-O2 in autotools and /O2 in VS).

I tried to run perf tool on linux:
perf record tesseract eurotext.tif eurotext
and I got this report (perf report):

  39,77%  tesseract  libtesseract.so.3.0.4  [.] tesseract::SquishedDawg::edge_char_of
  13,98%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ComputeCharNormArrays
  13,09%  tesseract  libtesseract.so.3.0.4  [.] IntegerMatcher::UpdateTablesForFeature
   4,22%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::PruneClasses
   2,66%  tesseract  libtesseract.so.3.0.4  [.] ScratchEvidence::UpdateSumOfProtoEvidences
   1,48%  tesseract  libtesseract.so.3.0.4  [.] ELIST_ITERATOR::forward
   1,16%  tesseract  libc-2.19.so           [.] _int_malloc
   1,15%  tesseract  libtesseract.so.3.0.4  [.] tesseract::ShapeTable::MaxNumUnichars
   1,01%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ExpandShapesAndApplyCorrections
   0,87%  tesseract  liblept.so.5.0.0       [.] rasteropLow
   0,79%  tesseract  libm-2.19.so           [.] __mul
   0,72%  tesseract  libtesseract.so.3.0.4  [.] FPCUTPT::assign
   0,71%  tesseract  libc-2.19.so           [.] _int_free
   0,71%  tesseract  libtesseract.so.3.0.4  [.] ELIST::add_sorted_and_find
   0,61%  tesseract  libtesseract.so.3.0.4  [.] tesseract::AmbigSpec::compare_ambig_specs
   0,57%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ComputeNormMatch
   0,52%  tesseract  libc-2.19.so           [.] memset
   0,49%  tesseract  libc-2.19.so           [.] vfprintf
   0,45%  tesseract  libc-2.19.so           [.] malloc
   0,36%  tesseract  libtesseract.so.3.0.4  [.] SegmentLLSQ
   0,31%  tesseract  libm-2.19.so           [.] __ieee754_atan2_sse2
   0,31%  tesseract  libc-2.19.so           [.] malloc_consolidate
   0,30%  tesseract  libtesseract.so.3.0.4  [.] LLSQ::add
   0,29%  tesseract  libtesseract.so.3.0.4  [.] GenericVector<tesseract::ScoredFont>::operator+=
   0,29%  tesseract  libtesseract.so.3.0.4  [.] _ZN14ELIST_ITERATOR7forwardEv@plt
   0,28%  tesseract  libtesseract.so.3.0.4  [.] tesseract::ComputeFeatures
   0,25%  tesseract  liblept.so.5.0.0       [.] pixScanForForeground
   0,24%  tesseract  libtesseract.so.3.0.4  [.] GenericVector<tesseract::ScoredFont>::reserve
   0,20%  tesseract  libtesseract.so.3.0.4  [.] C_OUTLINE::increment_step
   0,20%  tesseract  [kernel.kallsyms]      [k] clear_page

according this report 3 top function consumed 66% of "time".

Then I tried 4 pages (A4 ) tiff (G4 compressed):

  52,24%  tesseract  libtesseract.so.3.0.4  [.] tesseract::SquishedDawg::edge_char_of
  12,06%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ComputeCharNormArrays
  10,06%  tesseract  libtesseract.so.3.0.4  [.] IntegerMatcher::UpdateTablesForFeature
   3,57%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::PruneClasses
   1,90%  tesseract  libtesseract.so.3.0.4  [.] ScratchEvidence::UpdateSumOfProtoEvidences
...

Then I tried non eng image: perf record tesseract hebrew.png hebrew -l heb:

  27,79%  tesseract  libtesseract.so.3.0.4  [.] IntegerMatcher::UpdateTablesForFeature
  27,34%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ComputeCharNormArrays
   4,40%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::PruneClasses
   3,98%  tesseract  libtesseract.so.3.0.4  [.] ScratchEvidence::UpdateSumOfProtoEvidences
   3,05%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ComputeNormMatch
   2,36%  tesseract  libtesseract.so.3.0.4  [.] tesseract::ShapeTable::MaxNumUnichars
   2,05%  tesseract  libtesseract.so.3.0.4  [.] tesseract::Classify::ExpandShapesAndApplyCorrections
...