http://study.marearts.com/2014/04/opencv-study-mat-point-access-method.html
This article is a sample code.
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#include "opencv2/opencv.hpp" using namespace cv; using namespace std; int main(int, char) { namedWindow("img", 1); Mat img = imread("anapji.jpg"); if (img.depth() == CV_8U) printf("8bit unsigend\n"); img. /* cout << img.elemSize() << endl; cout << img.channels() << endl; cout << img.rows << endl; cout << img.step << endl; */ //using data //for (int i = img.rows / 10 * 7; i < img.rows / 10 * 8; i++) { //for (int i = 0; i < img.rows ; i++) { for (int i = img.rows / 10 * 7; i < img.rows / 10 * 8; i++) { for (int j = 0; j < img.cols; j++) { unsigned char r, g, b; b = img.data[i * img.step + j * img.elemSize() + 0]; g = img.data[i * img.step + j * img.elemSize() + 1]; r = img.data[i * img.step + j * img.elemSize() + 2]; img.data[i * img.step + j * img.elemSize() + 0] = unsigned char(255 - b); img.data[i * img.step + j * img.elemSize() + 1] = unsigned char(255 - g); img.data[i * img.step + j * img.elemSize() + 2] = unsigned char(255 - r); } } //using at for (int i = img.rows / 10 * 2; i < img.rows / 10 * 3; ++i) { for (int j = 0; j < img.cols; ++j) { //Vec3b means 'uchar 3ch' unsigned char b = img.at< cv::Vec3b>(i, j)[0]; unsigned char g = img.at< cv::Vec3b>(i, j)[1]; unsigned char r = img.at< cv::Vec3b>(i, j)[2]; //printf("%d %d %d\n", b, g, r); img.at< cv::Vec3b>(i, j)[0] = unsigned char(255 - b); //b img.at< cv::Vec3b>(i, j)[1] = unsigned char(255 - g); //g img.at< cv::Vec3b>(i, j)[2] = unsigned char(255 - r); //r } } //using ptr for (int i = img.rows / 10 * 5; i < img.rows / 10 * 6; i++) { cv::Vec3b* ptr = img.ptr< cv::Vec3b >(i); for (int j = 0; j < img.cols; j++) { unsigned char b1 = (ptr[j][0]); unsigned char g1 = (ptr[j][1]); //note!! unsigned char r1 = (ptr[j][2]); cv::Vec3b bgr = ptr[j]; unsigned char b2 = (bgr[0]); unsigned char g2 = (bgr[1]); //note!! unsigned char r2 = (bgr[2]); ptr[j] = cv::Vec3b(255 - b1, 255 - g1, 255 - r1); } } //using iteration cv::MatIterator_< cv::Vec3b> itd = img.begin< cv::Vec3b>(), itd_end = img.end< cv::Vec3b>(); for (int i = 0; itd != itd_end; ++itd, ++i) { cv::Vec3b bgr = (*itd); (*itd)[0] = 255 - bgr[0]; (*itd)[1] = 255 - bgr[1]; (*itd)[2] = 255 - bgr[2]; } imshow("img", img); //show waitKey(0); destroyAllWindows(); return 0; }..
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