textRotCorrect.cpp

/*
 *	Author: John Hany
 *	Website: http://johnhany.net
 *	Source code updates: https://github/johnhany/textRotCorrect
 *	If you have any advice, you could contact me at: johnhany@163.com
 *	Need OpenCV environment!
 *
 */

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>

using namespace cv;
using namespace std;

#define GRAY_THRESH 150
#define HOUGH_VOTE 100

//#define DEGREE 27

int main(int argc, char **argv)
{
	//Read a single-channel image
	const char* filename = "imageText.jpg";
	Mat srcImg = imread(filename, CV_LOAD_IMAGE_GRAYSCALE);
	if(srcImg.empty())
		return -1;
	imshow("source", srcImg);

	Point center(srcImg.cols/2, srcImg.rows/2);

#ifdef DEGREE
	//Rotate source image
	Mat rotMatS = getRotationMatrix2D(center, DEGREE, 1.0);
	warpAffine(srcImg, srcImg, rotMatS, srcImg.size(), 1, 0, Scalar(255,255,255));
	imshow("RotatedSrc", srcImg);
	//imwrite("imageText_R.jpg",srcImg);
#endif

	//Expand image to an optimal size, for faster processing speed
	//Set widths of borders in four directions
	//If borderType==BORDER_CONSTANT, fill the borders with (0,0,0)
	Mat padded;
	int opWidth = getOptimalDFTSize(srcImg.rows);
	int opHeight = getOptimalDFTSize(srcImg.cols);
	copyMakeBorder(srcImg, padded, 0, opWidth-srcImg.rows, 0, opHeight-srcImg.cols, BORDER_CONSTANT, Scalar::all(0));

	Mat planes[] = {Mat_<float>(padded), Mat::zeros(padded.size(), CV_32F)};
	Mat comImg;
	//Merge into a double-channel image
	merge(planes,2,comImg);

	//Use the same image as input and output,
	//so that the results can fit in Mat well
	dft(comImg, comImg);

	//Compute the magnitude
	//planes[0]=Re(DFT(I)), planes[1]=Im(DFT(I))
	//magnitude=sqrt(Re^2+Im^2)
	split(comImg, planes);
	magnitude(planes[0], planes[1], planes[0]);

	//Switch to logarithmic scale, for better visual results
	//M2=log(1+M1)
	Mat magMat = planes[0];
	magMat += Scalar::all(1);
	log(magMat, magMat);

	//Crop the spectrum
	//Width and height of magMat should be even, so that they can be divided by 2
	//-2 is 11111110 in binary system, operator & make sure width and height are always even
	magMat = magMat(Rect(0, 0, magMat.cols & -2, magMat.rows & -2));

	//Rearrange the quadrants of Fourier image,
	//so that the origin is at the center of image,
	//and move the high frequency to the corners
	int cx = magMat.cols/2;
	int cy = magMat.rows/2;

	Mat q0(magMat, Rect(0, 0, cx, cy));
	Mat q1(magMat, Rect(0, cy, cx, cy));
	Mat q2(magMat, Rect(cx, cy, cx, cy));
	Mat q3(magMat, Rect(cx, 0, cx, cy));

	Mat tmp;
	q0.copyTo(tmp);
	q2.copyTo(q0);
	tmp.copyTo(q2);

	q1.copyTo(tmp);
	q3.copyTo(q1);
	tmp.copyTo(q3);

	//Normalize the magnitude to [0,1], then to[0,255]
	normalize(magMat, magMat, 0, 1, CV_MINMAX);
	Mat magImg(magMat.size(), CV_8UC1);
	magMat.convertTo(magImg,CV_8UC1,255,0);
	imshow("magnitude", magImg);
	//imwrite("imageText_mag.jpg",magImg);

	//Turn into binary image
	threshold(magImg,magImg,GRAY_THRESH,255,CV_THRESH_BINARY);
	imshow("mag_binary", magImg);
	//imwrite("imageText_bin.jpg",magImg);

	//Find lines with Hough Transformation
	vector<Vec2f> lines;
	float pi180 = (float)CV_PI/180;
	Mat linImg(magImg.size(),CV_8UC3);
	HoughLines(magImg,lines,1,pi180,HOUGH_VOTE,0,0);
	int numLines = lines.size();
	for(int l=0; l<numLines; l++)
	{
		float rho = lines[l][0], theta = lines[l][1];
		Point pt1, pt2;
		double a = cos(theta), b = sin(theta);
		double x0 = a*rho, y0 = b*rho;
		pt1.x = cvRound(x0 + 1000*(-b));
		pt1.y = cvRound(y0 + 1000*(a));
		pt2.x = cvRound(x0 - 1000*(-b));
		pt2.y = cvRound(y0 - 1000*(a));
		line(linImg,pt1,pt2,Scalar(255,0,0),3,8,0);
	}
	imshow("lines",linImg);
	//imwrite("imageText_line.jpg",linImg);
	if(lines.size() == 3){
		cout << "found three angels:" << endl;
		cout << lines[0][1]*180/CV_PI << endl << lines[1][1]*180/CV_PI << endl << lines[2][1]*180/CV_PI << endl << endl;
	}

	//Find the proper angel from the three found angels
	float angel=0;
	float piThresh = (float)CV_PI/90;
	float pi2 = CV_PI/2;
	for(int l=0; l<numLines; l++)
	{
		float theta = lines[l][1];
		if(abs(theta) < piThresh || abs(theta-pi2) < piThresh)
			continue;
		else{
			angel = theta;
			break;
		}
	}

	//Calculate the rotation angel
	//The image has to be square,
	//so that the rotation angel can be calculate right
	angel = angel<pi2 ? angel : angel-CV_PI;
	if(angel != pi2){
		float angelT = srcImg.rows*tan(angel)/srcImg.cols;
		angel = atan(angelT);
	}
	float angelD = angel*180/(float)CV_PI;
	cout << "the rotation angel to be applied:" << endl << angelD << endl << endl;

	//Rotate the image to recover
	Mat rotMat = getRotationMatrix2D(center,angelD,1.0);
	Mat dstImg = Mat::ones(srcImg.size(),CV_8UC3);
	warpAffine(srcImg,dstImg,rotMat,srcImg.size(),1,0,Scalar(255,255,255));
	imshow("result",dstImg);
	//imwrite("imageText_D.jpg",dstImg);
	
	waitKey(0);

	return 0;
}