Opencv learning notes -day13 pixel value statistics calculation of maximum and minimum values, average values and standard deviations (use of minmaxloc() and meanstddev() functions)

day13 Pixel value statistics

function

1. minMaxLoc(); Max min statistics

CV_EXPORTS_W void minMaxLoc(InputArray src, CV_OUT double* minVal,
                            CV_OUT double* maxVal = 0, CV_OUT Point* minLoc = 0,
                            CV_OUT Point* maxLoc = 0, InputArray mask = noArray());

Parameters	explain
src	Enter a single channel array （ Images ）
minVal	double* type , The minimum value that the pointer points to . If there is no need to return , This value is set to NULL
maxVal	double* type , The maximum value that the pointer points to . If there is no need to return , This value is set to NULL
minLoc	Point* type , The pointer points to the position of the minimum value （ In two dimensions ）. If there is no need to return , This value is set to NULL.
maxLoc	Point* type , Returns the pointer to the maximum position （ In two dimensions ）. If there is no need to return , This value is set to NULL
mask	Optional mask for selecting subarrays

notes：1,minMaxLoc For single channel images ,minMaxIdx There is no limit to （ However, the output coordinates will become three-dimensional ）.
2, The first 6 Two parameters are optional (optional), No use, no transfer

example 1

minMaxLoc(mv[i], &minv, &maxv, &minLoc, &maxLoc, Mat());
// Statistics of single channel images mv[i] The maximum and minimum values in and the pointer to the maximum and minimum values 
//minMaxLoc() function   The input image （mv[i]） Single channel is required 

2. meanStdDev(); Mean and standard deviation statistics

CV_EXPORTS_W void meanStdDev(InputArray src, OutputArray mean, OutputArray stddev,
                             InputArray mask=noArray());

Parameters	explain
src	Input array （ Images ）1-4 All channels are OK
mean	mean value
stddev	Standard deviation
mask	Optional mask for selecting subarrays

example 2

meanStdDev(image, mean, stddev);
// Statistics image The mean and standard deviation of the three channels  

When printing mean.at< double >(0, 0),mean.at< double >(1, 0),mean.at< double> (2, 0)
Represent the mean values of the three channels respectively ,mean.at< double >(0, 0),mean.at< double >(0, 1),mean.at< double >(0, 2), They also represent the mean values of the three channels and correspond to the first three one by one ,

The standard deviation is the same
stddev.at< double >(i,0)

Code

quickopencv.h

#pragma once

#include <opencv2\highgui.hpp>

#include <opencv2\imgproc.hpp>

using namespace cv;
// Defining classes 
class QuickDemo{
    
public:
	void colorSpace_Demo(Mat &image);// Color space conversion function 2021-12-24
	void mat_creation_demo(Mat &image);//Mat Object and creation 2021-12-27
	void pixel_vist_Demo(Mat &image);// Read and write operation of image pixels 2022-1-3
	void operators_demo(Mat &image);// Arithmetic operation of image pixels 2022-1-4
	void tracking_bar_demo(Mat &image);// Scroll bar operation demonstration 2022-1-7
	void key_demo(Mat &image);// Keyboard response operation 2022-1-12
	void color_style_demo(Mat &image);//OpenCV With color table operation 2022-1-12
	void bitwise_demo(Mat &image);// Bit operation （ Logical operation ）2022-1-17
	void channels_demo(Mat &image);// Channel separation and merge 2022-1-17
	void inrange_demo(Mat &image);//roi Region extraction  2022-1-20
	void pixel_statistic_demo(Mat &image);// Pixel value statistics 2022-1-21
};

QuickDemo.cpp

 #include <opencv2\highgui.hpp>

#include <opencv2\imgproc.hpp>

#include<quickopencv.h>

#include <iostream>
void QuickDemo::pixel_statistic_demo(Mat &image)
{
    
	double minv, maxv;
	Point minLoc, maxLoc;// Location 
	std::vector<Mat> mv;
	split(image, mv);// The channel separation 
	for (int i = 0; i < mv.size(); i++)
	{
    
		minMaxLoc(mv[i], &minv, &maxv, &minLoc, &maxLoc, Mat());//minMaxLoc() function   Input image requires a single channel 
		std::cout << "No.vhannels." << i << " min value " << minv << " max value " << maxv << std::endl;
	}
	Mat mean, stddev;//mean: Average  stddev: variance 
	meanStdDev(image, mean, stddev);
	//CV_EXPORTS_W void meanStdDev(InputArray src, OutputArray mean, OutputArray stddev,InputArray mask = noArray());
	std::cout << "means：" << mean << std::endl;
	std::cout << "stddev：" << stddev << std::endl;
	// Print separately 
	for (int i = 0; i < mv.size(); i++)
	{
    
		std::cout <<"means："<< mean.at<double>(i, 0) <<"----"<<"stddev："<<stddev.at<double>(i,0)<< std::endl;// Single channel print average 
	}
}

OpencvTest.cpp

#include <iostream>
#include <opencv2\highgui.hpp>
#include <opencv2\imgproc.hpp>
#include<quickopencv.h>

using namespace cv;
using namespace std;

int main()
{
    
	Mat scr = imread("D:\\ Study \\OpenCV Study \\pictures\\image\\ Green screen Pikachu .jfif");// Open a picture 
	if (!scr.data == 1)// Sentenced to empty 
		return -1;
	namedWindow(" window 1", WINDOW_NORMAL);// establish  WINDOW_FREERATIO window 
	imshow(" window 1",scr);// Show in the created window 
	QuickDemo qd;
	qd.pixel_statistic_demo(scr);
	waitKey(0);
	return 0;
}

result ：