Getting Started

Example code taken from the Tesseract's github wiki page.

See also

https://github.com/tesseract-ocr/tesseract/wiki/APIExample

Basic example

#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;
}

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

It is possible to get confidence value and BoundingBox per word from a 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));
}

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;\n"
    "WritingDirection: %d\n"
    "TextlineOrder: %d\n"
    "Deskew angle: %.4f\n",
    orientation, direction, order, deskew_angle);

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)));
}