tesseract 4 android build issue

[romaderi]

Hi I have juste replaced the jni\com_googlecode_tesseract_android\src in the tess two project with 4.0 tesseract src and try to compile it with ndkbuild. I'm facing an issue with the following error ...
[armeabi] Install : libjpgt.so => libs/armeabi/libjpgt.so
[armeabi] Install : liblept.so => libs/armeabi/liblept.so
[armeabi] Install : libpngt.so => libs/armeabi/libpngt.so
[armeabi] Compile++ thumb: tess <= lstm.cpp
jni/com_googlecode_tesseract_android/src/lstm/lstm.cpp:85:64: error: use of
undeclared identifier 'log2'
nf_ = type_ == NT_LSTM_SOFTMAX ? no_ : IntCastRounded(ceil(log2(no_)));
^
jni/com_googlecode_tesseract_android/src/lstm/lstm.cpp:183:31: error: use of
undeclared identifier 'log2'
nf_ = IntCastRounded(ceil(log2(no_)));
^
2 errors generated.
make: *** [obj/local/armeabi/objs/tess/src/lstm/lstm.o] Error 1

Any idea ?

[stweil]

It looks like log2 is not provided by Android. See this discussion which also includes valid solutions.

Tesseract already uses its own log2 for Android in wordrec/language_model.cpp.

[raulcorreia1]

Hi romaderi, I am also trying to build tesseract 4 using the base of tess-two, to prevent the log2 issue I think you need to add the code below before the namespace in lstm.cpp and weightmatrix.cpp:

#if (defined(_MSC_VER) && _MSC_VER < 1900) || defined(ANDROID)
double log2(double n) {
  return log(n) / log(2.0);
}
#endif  // _MSC_VER

Now after doing that I found some other errors:

Error:error: assigning to 'PROGRESS_FUNC' (aka 'bool (*)(int, int, int, int, int)') from incompatible type 'bool (void *, int, int, int, int, int)': different number of parameters (5 vs 6)

Not sure how to solve this one...

[avestnik]

hi! I faced the same problem, was able to fix it inserting log2() implementation into lstm.cpp and weightmatrix.cpp. I guess it would be nice if source code maintainers fix it in upstream

[Shreeshrii]

@stweil

Can this be fixed in the repo?

Related issue posted in the forum

https://groups.google.com/d/msgid/tesseract-ocr/bdf690c6-7979-4ed6-a62d-f8b67853c6c0%40googlegroups.com?utm_medium=email&utm_source=footer

[stweil]

Sure. The easy solution would use the code shown above, but I want to replace the log function by faster pure integer calculations here (which needs a little bit more time to implement it).

[Shreeshrii]

@stweil Would it make sense to implement the easy solution now and revert it when you replace the log function later?

[amitdo]

Related: android/ndk#82

[stweil]

The issue is addressed by pull request #1353.

[rezaee]

Hi there,
May you tell me where can I get the tesseract-4 source and which folder exactly should replace with which one?
I am newbie and want to use tesseract-4 on my Android applications!

I did git clone git://github.com/tesseract-ocr/tesseract.git but don't know should replace which folder with jni\com_googlecode_tesseract_android\src inside tess-two folder?

[amitdo]

Android has log2() now.
https://developer.android.com/ndk/guides/cpp-support#libc

[stweil]

That's good. And the Tesseract code has code which supports older installations without log2 since some time. @romaderi, could you please close this issue, or do you think there is still a problem?

[amitdo]

I think the log2() for android is obsolete.

The older NDKs that needed that custom code are no longer supported by Google. AFAIK, new NDKs can be used to build apps for old android releases.