Tesseract:Correcting page orientation
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Recently for work I had to deal with doing OCR over inverted pages, something like this courier-black-300-mod.png

I came across some threads(1, 2, 3)on tesseract google group and StackOverflow which were close to problem I was dealing with. I tried example mentioned on tesseract API page, looked at OSDetect code(4) and though it has already couple of implementations like updatebestorientation somehow it was not working for me. Maybe I was doing something wrong but eventually I ended up with following code which works for me, it rotates the page despite the top line.

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

int main(int argc, char **argv)
    OSResults os_results;
    tesseract::TessBaseAPI *api = new tesseract::TessBaseAPI();
    if (api->Init(NULL, "eng")) {
	fprintf(stderr, "Could not initialize tesseract.\n");
    Pix *image = pixRead(filename);
    // To detect correct OS and flip images
    OrientationDetector os_detector = OrientationDetector(&os_results);
    int correct_orientation = os_detector.get_orientation();
    // Had to add this condition because get_orientation result and
    // pixRotateOrth were not in sync.
    if (correct_orientation == 1) {
	image = pixRotate90(image, -1);
    else if (correct_orientation == 3) {
	image = pixRotate90(image, 1);
    else if (correct_orientation == 2) {
	pixRotate180(image, image);
    char* ocrResult = api->GetUTF8Text();
    fprintf(stdout, "Recognized Text: %s\n", ocrResult);
    delete [] ocrResult;
    return 0;