Hi, I want to count colors in an image. I read many suggestion to use Histogram, so I followed instruction from OpenCV docs Histogram Calculation. But how exactly to read this histogram to get information about how many color is in there ?
histograms are not really useful for what you wanted. sure, for a single channel you could count the non-zero bins, but if you have 2 channels, your histogram is a 2d matrix, and for 3 channels a 3d cube, that's not practical.
but we can make integer (hex) numbers from our pixels, and collect them in a std::set, which will only keep the unique values:
std::set<int> unique;
// iterate over pixels (assummes: CV_8UC3 !)
for (Vec3b &p : cv::Mat_<Vec3b>(image)) {
// "hash" representation of the pixel
int n = (p[0] << 16) | (p[1] << 8) | (p[2]);
unique.insert(n);
}
cout << "we have " << unique.size() << " unique colors:" << endl;
for (int i: unique)
cout << format("%06x", i) << endl;
Asked: 2018-12-13 06:05:40 -0600
Seen: 875 times
Last updated: Dec 13 '18
can you explain some more about it ?
basically, hstograms count color occurences into bins. (and there are as many colour, as yoou gave it bins.) is that really, what you wanted ?
did you want to find out, how many unique combinations of B,G,R are present in your image ?
| can you explain some more about it ?
exactly count how many colors.
(edit) yes, unique colors. is that possible with histogram ?