转自：https://code.google.com/p/tesseract-ocr/wiki/APIExample
APIExample
API examples
Updated Aug 12, 2014 by [email protected]
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 his platform, though basic compilation examples are included for beginners with Linux.
More details about tesseract-ocr API can found at baseapi.h
- Basic example
- example
- Result iterator example
- Orientation and script detection (OSD) example
- Example of iterator over the classifier choices for a single symbol
- Compiling C++ API programs on Linux
- C-API in python
- Example using the C-API in a C program
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-3.02/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-3.02/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 posibility to get confidence value and BoundingBox per word from ResultIterator:
Pix *image = pixRead("/usr/src/tesseract-3.02/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 posibility to use other PageiteratorLevel.
Orientation and script detection (OSD) example
const char* inputfile = "/usr/src/tesseract-3.02/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-3.02/", "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-3.02/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 ctypes
lang = "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 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;}
On Linux you can compile it as you would build a program using the C++ API.