OpenCV(4): Mat對象

注：轉載請標明原文出處鏈接：https://xiongyiming.blog.csdn.net/article/details/106931100

1基礎知識

Mat對象 OpenCV2.0之後引進的圖像數據結構、自動分配內存、不存在內存泄漏的問題，是面向對象的數據結構。Mat對象分爲頭部 和 數據兩個部分。

IplImage 是從2001年OpenCV發佈之後就一直存在，是C語言風格的數據結構，需要開發者自己分配與管理內存，對大的程序使用它容易導致內存泄漏問題。IplImage從本質上講，它是Mat對象，但它還有其他一些成員變量將矩陣解釋爲圖像。

Mat對象構造函數有：

Mat();
Mat(int rows, int cols, int type);
Mat(Size size, int type)
Mat(int rows, int cols, int type, const Scalar $s);
Mat(int ndims, const int *sizes, int type);
Mat(int ndims, const int *sizes, int type, const Scalar &s);

Mat對象常用的函數有：

void copyTo(Mat mat);
void convertTo(Mat dst, int type);
Mat clone();
int channels();
int depth();
bool empty();
uchar* ptr(i=0);

Mat對象使用的注意事項
(1) 部分複製：一般情況下只會複製Mat對象的頭部和指針部分，不會複製數據部分

Mat A= imread(imgFilePath);
Mat B(A)  // 只複製

(2) 完全複製：如果把Mat對象的頭部和數據部分一起復制，可以通過如下兩個代碼

實現
Mat F = A.clone(); 
或 
Mat G; 
A.copyTo(G);

Mat對象使用的四個要點

1. 輸出圖像的內存是自動分配的；
2. 使用OpenCV的C++接口，不需要考慮內存分配問題；
3. 賦值操作和拷貝構造函數只會複製頭部分；
4. 使用clone與copyTo兩個函數實現數據完全複製；

2 代碼示例

2.1 創建一張空白圖像

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);


	Mat dst; 
	dst = Mat(src.size(), src.type()); //或者用 dst.create(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);


	waitKey(0);

	return 0;
}

運行結果

2.2 clone

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);

	/*
	Mat dst; 
	dst = Mat(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);
	*/
	Mat dst = src.clone();
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);


	waitKey(0);

	return 0;
}

運行結果

2.3 cvtcolor

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);

	/*
	Mat dst; 
	dst = Mat(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);
	*/
	Mat dst; 
	src.copyTo(dst);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);


	waitKey(0);

	return 0;
}

運行結果

2.4 channels

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);

	/*
	Mat dst; 
	dst = Mat(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);
	*/
	Mat dst; 

	
	cvtColor(src, dst, CV_BGR2GRAY);
	printf("原始圖像的通道數爲：%d\n", src.channels());
	printf("輸出圖像的通道數爲：%d\n", dst.channels());

	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);


	waitKey(0);

	return 0;
}

運行結果

2.5 cols、rows 和 uchar* ptr

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);

	/*
	Mat dst; 
	dst = Mat(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);
	*/

	Mat dst; 
	
	cvtColor(src, dst, CV_BGR2GRAY);
	printf("原始圖像的通道數爲：%d\n", src.channels());
	printf("輸出圖像的通道數爲：%d\n", dst.channels());

	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);

	
	int rows = dst.rows;
	int cols = dst.cols;
	printf("rows = %d , cols = %d\n", rows, cols);

	const uchar* firstRow = dst.ptr<uchar>(0);
	printf("first pixel value = %d\n", *firstRow);

	waitKey(0);

	return 0;
}

運行結果

2.6 構建一個窗口

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);

	/*
	Mat dst; 
	dst = Mat(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);
	*/
	Mat dst; 

	
	cvtColor(src, dst, CV_BGR2GRAY);
	printf("原始圖像的通道數爲：%d\n", src.channels());
	printf("輸出圖像的通道數爲：%d\n", dst.channels());

	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);

	
	int rows = dst.rows;
	int cols = dst.cols;
	printf("rows = %d , cols = %d\n", rows, cols);

	const uchar* firstRow = dst.ptr<uchar>(0);
	printf("first pixel value = %d\n", *firstRow);

	Mat M1(3, 3, CV_8UC3, Scalar(255, 255, 255));
	cout << "M1=" << endl << M1 << endl;


	waitKey(0);

	return 0;
}

運行結果

注意

1. 對於int類型8位，CvMat矩陣對應的參數類型爲 CV_8UC1、CV_8UC2、CV_8UC3 (其中，數字1、2、3表示通道數，比如 RGB 圖像有3通道，就用CV_8UC3，灰度圖像就用CV_8UC1)
2. 對於float類型32位，對應CvMat數據結構參數爲：CV_32FC1、CV_32FC2、CV_32FC3等；
3. 對於double 類型64位，對應CvMat數據結構參數爲：CV_64FC1、CV_64FC2、CV_64FC3等。

2.7 zeros

代碼

#include <opencv2/core/core.hpp> 
#include <opencv2/imgcodecs.hpp> 
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/highgui/highgui_c.h>

#include <iostream>
#include <math.h>




using namespace cv;
using namespace std;
int main(int argc, char** args) {
	Mat src = imread("ZXP1.jpg", IMREAD_UNCHANGED);
	if (src.empty()) {
		cout << "could not find the image resource..." << std::endl;
		return -1;
	}
	namedWindow("Original Image", CV_WINDOW_AUTOSIZE);
	imshow("Original Image", src);

	/*
	Mat dst; 
	dst = Mat(src.size(), src.type());
	dst = Scalar(255, 255, 255);
	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);
	*/
	Mat dst; 

	
	cvtColor(src, dst, CV_BGR2GRAY);
	printf("原始圖像的通道數爲：%d\n", src.channels());
	printf("輸出圖像的通道數爲：%d\n", dst.channels());

	namedWindow("Output Image", CV_WINDOW_AUTOSIZE);
	imshow("Output Image", dst);

	

	Mat M2 = Mat::zeros(3, 3, CV_8UC1);
	cout << "M2=" << endl << M2 << endl;


	waitKey(0);

	return 0;
}

運行結果

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參考資料

[1] https://edu.51cto.com/course/7521.html?source=so