c++ - Gamma Correction with pow -

i use gamma correction image. so, have pow every pixel intensity of source image g = 0.6. have problem cause destination image wrong. maybe have casting problem when take pixel source image. here code:

#include <opencv2/core.hpp> #include <opencv2/highgui/highgui.hpp> #include <iostream> #include <opencv2/imgproc/imgproc.hpp>  using namespace cv; using namespace std;   int main() {      mat src = imread("spine1.jpeg");       mat dst = mat(src.rows, src.cols, cv_8uc1);     cvtcolor(src, src, cv_8uc1);     dst = scalar(0);      (int x = 0; x < src.rows; x++) {         (int y = 0; y < src.cols; y++) {             int pixelvalue = (int)src.at<uchar>(x, y);              dst.at<uchar>(x, y) = pow(pixelvalue, 0.6);          }     }        namedwindow("input", cv_window_autosize);     namedwindow("output", cv_window_autosize);      imshow("input", src);     imshow("output", dst);      waitkey(0);     return 0; } 

edit: change cvtcolor(src, src, cv_8uc1); in cvtcolor(src, src, color_bgr2gray);

the call cvtcolor wrong. should use:

cvtcolor(src, src, color_bgr2gray); 

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also, can make code simpler, , less error prone:

#include <opencv2/opencv.hpp>  int main() {     // load image grayscale     cv::mat1b src = cv::imread("path_to_img", cv::imread_grayscale);      // convert double "pow"     cv::mat1d dsrc;     src.convertto(dsrc, cv_64f);      // compute "pow"     cv::mat1d ddst;     cv::pow(dsrc, 0.6, ddst);      // convert uchar     cv::mat1b dst;     ddst.convertto(dst, cv_8u);      // show results     imshow("src", src);     imshow("dst", dst);     waitkey();      return 0; }