gistfile1.cpp

// countnonzeropixels.cpp: count the number of non zero value pixels in an image and print it

#include <opencv2/core.hpp>
#include <opencv2/imgcodecs.hpp>

using namespace cv;
using namespace std;


int main(int argc, char *argv[])
{
    char *fname = argv[1];
    
    if (argc != 2) {
        fprintf(stderr, "usage: countnonzeropixels img.jpg\n");
        exit(1);
    }
    
    Mat img = imread(fname);
    
    unsigned n = 0;
    for(int y=0; y<img.rows; y++){
        uchar* img_ptr = img.ptr<uchar>(y);
        for(int x=0; x<img.cols; x++){
            if( img_ptr[x*3] == 0 ){
                n++;
            }
        }
    }
    
    unsigned totpix = img.rows*img.cols;
    
    printf("%d black pixels out of %d total (%0.3f%%)\n",
           n,totpix,100*n/(float)totpix);
    
    return 0;
}