tesseract OCR 调用的方法例程，from wiki



API examples

This wiki provide simple example how to use tesseract-ocr API (v3.02.02) in C++. It is expected that tesseract-ocr is correctly installed including all dependecies. It is expected that user is familiar with C++, compiling and linking program on their platform, though basic compilation examples are included for beginners with Linux.

More details about tesseract-ocr API can found at baseapi.h

Basic example

Code:

#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("/usr/src/tesseract/testing/phototest.tif");    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;}

Program must be linked to tesseract-ocr library and leptonica library.

If you want to restrict recognition to a sub-rectangle of the image - call SetRectangle(left, top, width, height) after SetImage. Each SetRectangle clears the recogntion results so multiple rectangles can be recognized with the same image. E.g.

  api->SetRectangle(30, 86, 590, 100);

GetComponentImages example

  Pix *image = pixRead("/usr/src/tesseract/testing/phototest.tif");  tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();  api->Init(NULL, "eng");  api->SetImage(image);  Boxa* boxes = api->GetComponentImages(tesseract::RIL_TEXTLINE, true, NULL, NULL);  printf("Found %d textline image components.\n", boxes->n);  for (int i = 0; i < boxes->n; i++) {    BOX* box = boxaGetBox(boxes, i, L_CLONE);    api->SetRectangle(box->x, box->y, box->w, box->h);    char* ocrResult = api->GetUTF8Text();    int conf = api->MeanTextConf();    fprintf(stdout, "Box[%d]: x=%d, y=%d, w=%d, h=%d, confidence: %d, text: %s",                    i, box->x, box->y, box->w, box->h, conf, ocrResult);  }

Result iterator example

There is possibility to get confidence value and BoundingBox per word from ResultIterator:

  Pix *image = pixRead("/usr/src/tesseract/testing/phototest.tif");  tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();  api->Init(NULL, "eng");  api->SetImage(image);  api->Recognize(0);  tesseract::ResultIterator* ri = api->GetIterator();  tesseract::PageIteratorLevel level = tesseract::RIL_WORD;  if (ri != 0) {    do {      const char* word = ri->GetUTF8Text(level);      float conf = ri->Confidence(level);      int x1, y1, x2, y2;      ri->BoundingBox(level, &x1, &y1, &x2, &y2);      printf("word: '%s';  \tconf: %.2f; BoundingBox: %d,%d,%d,%d;\n",               word, conf, x1, y1, x2, y2);      delete[] word;    } while (ri->Next(level));  }

Of course there is possibility to use other PageiteratorLevel.

Orientation and script detection (OSD) example

  const char* inputfile = "/usr/src/tesseract/testing/eurotext.tif";  tesseract::Orientation orientation;  tesseract::WritingDirection direction;  tesseract::TextlineOrder order;  float deskew_angle;  PIX *image = pixRead(inputfile);  tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();  api->Init("/usr/src/tesseract/", "eng");  api->SetPageSegMode(tesseract::PSM_AUTO_OSD);  api->SetImage(image);  api->Recognize(0);  tesseract::PageIterator* it =  api->AnalyseLayout();  it->Orientation(&orientation, &direction, &order, &deskew_angle);  printf("Orientation: %d;\nWritingDirection: %d\nTextlineOrder: %d\n" \         "Deskew angle: %.4f\n",         orientation, direction, order, deskew_angle);

Explanation for result codes are in publictypes.h

Example of iterator over the classifier choices for a single symbol

  Pix *image = pixRead("/usr/src/tesseract/testing/phototest.tif");  tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();  api->Init(NULL, "eng");  api->SetImage(image);  api->SetVariable("save_blob_choices", "T");  api->SetRectangle(37, 228, 548, 31);  api->Recognize(NULL);  tesseract::ResultIterator* ri = api->GetIterator();  tesseract::PageIteratorLevel level = tesseract::RIL_SYMBOL;  if(ri != 0) {      do {          const char* symbol = ri->GetUTF8Text(level);          float conf = ri->Confidence(level);          if(symbol != 0) {              printf("symbol %s, conf: %f", symbol, conf);              bool indent = false;              tesseract::ChoiceIterator ci(*ri);              do {                  if (indent) printf("\t\t ");                  printf("\t- ");                  const char* choice = ci.GetUTF8Text();                  printf("%s conf: %f\n", choice, ci.Confidence());                  indent = true;              } while(ci.Next());          }          printf("---------------------------------------------\n");          delete[] symbol;      } while((ri->Next(level)));  }

Compiling C++ API programs on Linux

Including and linking to Tesseract's API is done in a standard Linux way. To compile a basic program against the API, you can use a command like this:

g++ -o myprogram myprogram.cpp -llept -ltesseract

If Tesseract is installed in an unusual place, you can specify the include and lib directories explicitly with g++'s -I and -L flags, like this:

g++ -o myprogram myprogram.cpp -I/home/nick/local/include/tesseract -L/home/nick/local/lib -llept -ltesseract

C-API in python

Tesseract-ocr from version 3.02.02 provide C-API. This enable to use tesseract-ocr shared library in python (and other languages that can use C libraries):

import osimport ctypeslang = "eng"filename = "/usr/src/tesseract-ocr/phototest.tif"libname = "/usr/local/lib64/libtesseract.so.3"TESSDATA_PREFIX = os.environ.get('TESSDATA_PREFIX')if not TESSDATA_PREFIX:    TESSDATA_PREFIX = "../"tesseract = ctypes.cdll.LoadLibrary(libname)tesseract.TessVersion.restype = ctypes.c_char_ptesseract_version = tesseract.TessVersion()api = tesseract.TessBaseAPICreate()rc = tesseract.TessBaseAPIInit3(api, TESSDATA_PREFIX, lang)if (rc):    tesseract.TessBaseAPIDelete(api)    print("Could not initialize tesseract.\n")    exit(3)text_out = tesseract.TessBaseAPIProcessPages(api, filename, None, 0)result_text = ctypes.string_at(text_out)print 'Tesseract-ocr version', tesseract_versionprint result_text

Example of passing python file object to C-API can be found at pastebin.

Example of extracting orientation from Tesseract 4.0:

# /usr/bin/env python3# coding: utf-8PATH_TO_LIBTESS = '/path/to/development/libtesseract.so'import cffi  # requires "pip install cffi"ffi = cffi.FFI()ffi.cdef("""struct Pix;typedef struct Pix PIX;PIX * pixRead ( const char *filename );char * getLeptonicaVersion (  );typedef struct TessBaseAPI TessBaseAPI;typedef int BOOL;const char* TessVersion();TessBaseAPI* TessBaseAPICreate();int TessBaseAPIInit3(TessBaseAPI* handle, const char* datapath, const char* language);void TessBaseAPISetImage2(TessBaseAPI* handle, struct Pix* pix);BOOL   TessBaseAPIDetectOrientationScript(TessBaseAPI* handle, char** best_script_name,                                                             int* best_orientation_deg, float* script_confidence,                                                             float* orientation_confidence);""")libtess = ffi.dlopen(PATH_TO_LIBTESS)from ctypes.util import find_libraryliblept = ffi.dlopen(find_library('lept'))ffi.string(libtess.TessVersion())ffi.string(liblept.getLeptonicaVersion())api = libtess.TessBaseAPICreate()libtess.TessBaseAPIInit3(api, ffi.NULL, ffi.NULL)pix = liblept.pixRead('mono.png'.encode())libtess.TessBaseAPISetImage2(api, pix)script_name = ffi.new('char **')orient_deg = ffi.new('int *')script_conf = ffi.new('float *')orient_conf = ffi.new('float *')libtess.TessBaseAPIDetectOrientationScript(api, script_name, orient_deg, script_conf, orient_conf)ffi.string(script_name[0])print(orient_deg[0])print(script_conf[0])print(orient_conf[0])

Example using the C-API in a C program

The C-API can of course also be used by regular C programs, as in this very basic example.

#include <stdio.h>#include <allheaders.h>#include <capi.h>void die(const char *errstr) {fputs(errstr, stderr);exit(1);}int main(int argc, char *argv[]) {TessBaseAPI *handle;PIX *img;char *text;if((img = pixRead("img.png")) == NULL)die("Error reading image\n");handle = TessBaseAPICreate();if(TessBaseAPIInit3(handle, NULL, "eng") != 0)die("Error initialising tesseract\n");TessBaseAPISetImage2(handle, img);if(TessBaseAPIRecognize(handle, NULL) != 0)die("Error in Tesseract recognition\n");if((text = TessBaseAPIGetUTF8Text(handle)) == NULL)die("Error getting text\n");fputs(text, stdout);TessDeleteText(text);TessBaseAPIEnd(handle);TessBaseAPIDelete(handle);pixDestroy(&img);return 0;}