I am trying to calculate the skew of text in an image so I can correct it for the best OCR results.
Currently this is the function I am using:
double compute_skew(Mat &img)
{
// Binarize
cv::threshold(img, img, 225, 255, cv::THRESH_BINARY);
// Invert colors
cv::bitwise_not(img, img);
cv::Mat element = cv::getStructuringElement(cv::MORPH_RECT, cv::Size(5, 3));
cv::erode(img, img, element);
std::vector<cv::Point> points;
cv::Mat_<uchar>::iterator it = img.begin<uchar>();
cv::Mat_<uchar>::iterator end = img.end<uchar>();
for (; it != end; ++it)
if (*it)
points.push_back(it.pos());
cv::RotatedRect box = cv::minAreaRect(cv::Mat(points));
double angle = box.angle;
if (angle < -45.)
angle += 90.;
cv::Point2f vertices[4];
box.points(vertices);
for(int i = 0; i < 4; ++i)
cv::line(img, vertices[i], vertices[(i + 1) % 4], cv::Scalar(255, 0, 0), 1, CV_AA);
return angle;
}
When I look at then angle in debug I get 0.000000
However when I give it this image I get proper results of a skew of about 16 degrees:
How can I properly detect the skew in the first image?
