最近要实现OCR功能， 决定用tesseract。最新的稳定版本是3.04. github上有很好的安装教程，但是公司的server是centos 6，和ubuntu还有一点区别。

leptonica-1.73

tessaract需要用到leptonica, 安装leptonica需要另外一些库, ubuntu下的这些库，不知为何centos要用不同的名字：

#ubuntu
sudo apt-get install autoconf automake libtool
sudo apt-get install pkg-config
sudo apt-get install libpng12-dev
sudo apt-get install libjpeg8-dev
sudo apt-get install libtiff5-dev
sudo apt-get install zlib1g-dev

#centos
sudo yum -y install libtiff libtiff-devel libjpeg-devel libpng-deve

下载

git clone https://github.com/DanBloomberg/leptonica.git
git tag -l
git checkout tags/v1.73
git checkout -b 1.73

官方安装教程。1.73提供了cmake编译，但是不知道问什么不支持cmake之后不能make install(??)。所以最后还是选择autoconf, 之后configure指定安装路径（统一用/local/ydong/ocrlib/libs）,得到头文件和库：

./configure --prefix=/local/ydong/ocrlib/libs
make
make install

Tesseract 3.04

下载:

git clone https://github.com/tesseract-ocr/tesseract.git
git branch -v -a
git checkout -b 3.04 remotes/origin/3.04

安装

./autogen.sh \\ 生成configure file
export LIBS="stdc++" \\ 或者添加 LIBS=“stdc++”到configure file的头部。否则会编译出错
./configure --with-extra-libraries=/local/ydong/ocrlib/libs/lib/ --prefix=/local/ydong/ocrlib/libs/ \\extra lib里是leptonica
make
make install

下载pretrained model

cd /local/ydong/ocrlib/
mkdir data
cd data
wget https://github.com/tesseract-ocr/tessdata/archive/master.zip
unzip master.zip
mv /local/ydong/ocrlib/data/tessdata-master /local/ydong/ocrlib/data/tessdata
export TESSDATA_PREFIX=/local/ydong/ocrlib/data //用环境变量指定model的路径

调用API

官方提供了一个简单的调用API的教程。试着编译一下，顺便复习下Makefile和LD_LIBARRY_PATH etc.

cd /local/ydong/ocrlib/
mkdir app

main.cpp:

#include <tesseract/baseapi.h>
#include <leptonica/allheaders.h>

int main()
{
    char *outText;

    tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();
    // Initialize tesseract-ocr with English, without specifying tessdata path
    if (api->Init(NULL, "eng")) {
        fprintf(stderr, "Could not initialize tesseract.\n");
        exit(1);
    }

    // Open input image with leptonica library
    Pix *image = pixRead("/local/ydong/ocrlib/tesseract/testing/phototest.tif"); //use your own path
    api->SetImage(image);
    // Get OCR result
    outText = api->GetUTF8Text();
    printf("OCR output:\n%s", outText);

    // Destroy used object and release memory
    api->End();
    delete [] outText;
    pixDestroy(&image);

    return 0;
}

Makefile:

CXX = g++
CFLAGS = -g -O2 -std=c++11
LIBS = -lstdc++ -llept -ltesseract
INCLUDES = -I/local/ydong/ocrlib/libs/include/
LFLAGS = -L/local/ydong/ocrlib/libs/lib/

all: ocr-test
ocr-test: main.cpp
        $(CXX) $(CFLAGS) $(INCLUDES) $(LFLAGS) $(LIBS) -o ocr-test main.cpp

编译运行：

make
./ocr-test

动态库链接，rpath，LD_LIBRARY_PATH

查找动态库的优先级，rpath优先级高于LD_LIBRARY_PATH
查看ocr-test用到的动态库

ldd ocr-test
...
liblept.so.5 => /local/ydong/ocrlib/libs/lib/liblept.so.5 (0x00007f26891a0000)
libtesseract.so.3 => /local/ydong/ocrlib/libs/lib/libtesseract.so.3 (0x00007f2688a03000)
...

查看rpath

chrpath -l ocr-test
ocr-test: no rpath or runpath tag found.

rpath会领写一篇。
rpath
-Wl,-rpath -Wl,/local/ydong/ocrlib/libs/lib
$origin

g++ -g -O2 -std=c++11 -o .libs/tesseract tesseract-tesseractmain.o  -L/local/ydong/ocrlib/libs/lib/ ./.libs\
/libtesseract.so -lrt /local/ydong/ocrlib/libs/lib/liblept.so -lm -lz -lpng -ljpeg -ltiff -lpthread -Wl,-rpath -Wl\
,/local/ydong/ocrlib/libs/lib