How to compute maximum pixel value of Mat in OpenCV [duplicate]

Question

This should be obvious, I thought. But I can't find easy way to find maximum among all pixels in a Mat of OpenCV. Of course, I can do following for each pixel type. But general max function would be still useful.

double cvMax(cv::Mat& mat)
{
float max=0;
float* pData=(float*)mat.data;
for(int i=0;i<mat.rows;i++) 
{
    for(int j=0;j<mat.cols;j++)
    {
        float value = pData[j+i*mat.cols];
        if(value>max) 
        {
            max=value;
        }
    }
}
return max;
}

Answer 1

cv::minMaxIdx is really simple to use. It looks complicated in the docs, but you can omit most of the parameters:

Mat m = ...;

double min, max;
minMaxIdx(m, &min, &max);

printf("min: %f, max: %f\n", min, max);

Moreover, cv::minMaxIdx is more than 10 times faster than std::max_element. This is because cv::minMaxIdx is optimized for handling cv::Mat data and it uses multiple threads if possible.

If you also need the locations of the minimum and maximum in the image, you can use cv::minMaxLoc.