Build Tesseract 5 in Conda Environment

 

Here’s a short guide to building Tesseract 5 from source (master branch on GitHub).

I’m writing this mainly because conda offers as packages only versions of Tesseract up to 4.1.1 – at least at this moment. The other reason is that the cluster I’m compiling Tesseract on is running a CentOS 7 and permitting only inside-environment changes so I can’t install packages with yum.

In this guide I’m using gcc/g++ version 6.2.0; it is recommended to use recent versions when compiling Tesseract 5. For example, the build fails with gcc/g++ 4.8.5.

Building Steps

1. Create your conda environment and activate it:

(tess-build) [dan.sporici@hpsl-wn02 tesseract]$ ./tesseract -v
tesseract 5.0.0-alpha-781-gb19e3
leptonica-1.78.0
libgif 5.2.1 : libjpeg 9d : libpng 1.6.37 : libtiff 4.1.0 : zlib 1.2.11 : libwebp 1.0.2 : libopenjp2 2.3.1
Found AVX
Found SSE
Found OpenMP 201511

8. (tess-build) [dan.sporici@hpsl-wn02 tesseract]$ ./tesseract --list-langs
   List of available languages (1):
   eng
   

Possible Leptonica Linking Issue

/usr/bin/ld: warning: libpng16.so.16, needed by /.conda/envs/tess-build/lib/liblept.so, not found (try using -rpath or -rpath-link)
/usr/bin/ld: warning: libjpeg.so.9, needed by /.conda/envs/tess-build/lib/liblept.so, not found (try using -rpath or -rpath-link)
/usr/bin/ld: warning: libgif.so.7, needed by /.conda/envs/tess-build/lib/liblept.so, not found (try using -rpath or -rpath-link)
/usr/bin/ld: warning: libwebp.so.7, needed by /.conda/envs/tess-build/lib/liblept.so, not found (try using -rpath or -rpath-link)
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `png_create_read_struct@PNG16_0'
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `DGifOpen'
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `png_get_PLTE@PNG16_0'
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `jpeg_std_error@LIBJPEG_9.0' 
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `png_write_image@PNG16_0'
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `EGifPutScreenDesc'
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `EGifPutComment'
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `WebPEncodeRGBA'
[...]
/.conda/envs/tess-build/lib/liblept.so: undefined reference to `png_init_io@PNG16_0'
collect2: error: ld returned 1 exit status
make[2]: *** [tesseract] Error 1
make[2]: Leaving directory `/tesseract'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/tesseract'
make: *** [all] Error 2

This happens because the libraries in cause (libpng16.so, libjpeg.so, libgif.so, libwebp.so) are not found in the directories included in LD_LIBRARY_PATH. If step 5 doesn’t work (although it should), you might be able to get around this by modifying the Makefile and adding the libraries yourself after -llept:

LEPTONICA_LIBS = -L/.conda/envs/tess-build/lib -llept -lz -lpng16 -ljpeg -lgif -lwebp

If you follow this approach, you need to copy the libraries to tesseract/.libs otherwise you’ll get:

(tess-build) [dan.sporici@hpsl-wn02 tesseract]$ ./tesseract
/tesseract/.libs/lt-tesseract: error while loading shared libraries: liblept.so.5: cannot open shared object file: No such file or directory
/tesseract/.libs/lt-tesseract: error while loading shared libraries: libpng16.so.16: cannot open shared object file: No such file or directory
/tesseract/.libs/lt-tesseract: error while loading shared libraries: libjpeg.so.9: cannot open shared object file: No such file or directory
/tesseract/.libs/lt-tesseract: error while loading shared libraries: libgif.so.7: cannot open shared object file: No such file or directory 

That all; I hope this helps.

conda create --name tess-build 
conda activate tess-build

Install the following dependencies. You’ll need at least leptonica 1.74 for this to work - I’m using 1.78.0.

conda install -c conda-forge automake
conda install -c conda-forge libtool
conda install -c conda-forge pkgconfig
conda install -c conda-forge leptonica

Clone the latest Tesseract version from the master branch and navigate into the directory:

git clone https://github.com/tesseract-ocr/tesseract.git
cd tesseract

Run the following scripts to prepare the building process

./autogen.sh
./configure

Conda might not include the path to its libraries inside the LD_LIBRARY_PATH environment variable. I had to include it manually otherwise the build fails during linking:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:~/.conda/envs/tess-build/lib

Run the makefile:

make

Set the TESSDATA_PREFIX environment variable in order to inform Tesseract where to look for language packs; also download the eng (default) language pack into tessdata

export TESSDATA_PREFIX=$HOME/tesseract/tessdata
wget https://github.com/tesseract-ocr/tessdata/raw/master/eng.traineddata -P tessdata/

See if it works: