OpenCv 中Mat对象及其基本操作

$$Mat对象及其基本操作$$

1.Mat对象

Mat的定义

Mat(matrix矩阵):图像文件的内存数据对象
Mat:header (宽、高、通道数等信息)+ data（图像数据信息）

数据类型和通道信息

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {

	Mat src = imread("E:/cats.jpg", IMREAD_COLOR); // IMREAD_COLOR：加载为3通道彩色图像

	if (src.empty()) {
		printf("image is empty!!!");
		return -1;
	}

	namedWindow("image", WINDOW_FREERATIO); // WINDOW_NORMAL：可任意设置图像大小
	imshow("image", src);
	int width = src.cols;
	int height = src.rows;
	int dim = src.channels();
	printf("width : %d,height:%d,channels: %d",width,height,dim);
	waitKey(0);
	destroyAllWindows();
	return 0;
}

2 属性与操作

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {

	Mat src = imread("E:/cats.jpg", IMREAD_COLOR); // IMREAD_COLOR：加载为3通道彩色图像

	if (src.empty()) {
		printf("image is empty!!!");
		return -1;
	}

	namedWindow("image", WINDOW_FREERATIO); // WINDOW_NORMAL：可任意设置图像大小
	imshow("image", src);
	int width = src.cols; // 宽
	int height = src.rows;  // 高
	int dim = src.channels(); // 通道数
	int img_depth = src.depth();
	int img_type = src.type();
	printf("width : %d,height:%d,channels: %d,depth:%d,type: %d",width,height,dim, img_depth, img_type);
	waitKey(0);
	destroyAllWindows();
	return 0;
}

数据类型和通道类型：（0,16）和下表对应：CV_8U、 CV_8UC3

3 创建

• 3.1 创建空白Mat对象
• 从现有图像创建
• 创建填充值的Mat对象
• 创建单通道与多通道Mat对象
• 遍历与访问像素值

3.1 创建空白Mat对象

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {


	//- 创建空白Mat对象
	Mat t1 = Mat(256, 256, CV_8SC1);
	t1 = Scalar(0);
	imshow("t1", t1);

	Mat t2 = Mat(256, 256, CV_8SC3);
	t2 = Scalar(0, 255, 0);
	imshow("t2", t2);


	//- 从现有图像创建
	//- 创建填充值的Mat对象
	//- 创建单通道与多通道Mat对象
	//- 遍历与访问像素值
	waitKey(0);
	destroyAllWindows();
	return 0;
}

Mat(Size(512,512), CV_8SC1);

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {


	//- 创建空白Mat对象
	Mat t1 = Mat(Size(512,512), CV_8SC1);
	t1 = Scalar(0);
	imshow("t1", t1);

	Mat t2 = Mat(Size(512, 512), CV_8SC3);
	t2 = Scalar(0, 255, 0);
	imshow("t2", t2);

	waitKey(0);
	destroyAllWindows();
	return 0;
}

Mat::zeros(Size(256,256),CV_8SC1);

using namespace cv;
using namespace std;

int main(int argc, char** argv) {


	//- 创建空白Mat对象
	Mat t1 = Mat::zeros(Size(256,256),CV_8SC1);
	imshow("t1", t1);

	waitKey(0);
	destroyAllWindows();
	return 0;
}

3.2 从现有图像创建

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {

	Mat src = imread("E:/cats.jpg", IMREAD_COLOR); // IMREAD_COLOR：加载为3通道彩色图像

	if (src.empty()) {
		printf("image is empty!!!");
		return -1;
	}

	// create from src
	// 修改t1即修改src,t2  clone t1,修改t1 所以 t2也会变
	// 但是修改克隆t1的t2改变，t1不会变
	Mat t1 = src;
	t1 = Scalar(0, 255, 0);
	Mat t2 = src.clone();  // src.copyTo(t2)
	imshow("t2", t2);

	// 创建源图大小一样的全零矩阵
	Mat t3 = Mat::zeros(src.size(), src.type());
	imshow("t3", t3);


	waitKey(0);
	destroyAllWindows();
	return 0;
}

创建源图大小一样的全零矩阵

Mat t3 = Mat::zeros(src.size(), src.type());
imshow("t3", t3);

4 遍历访问每个像素值

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {

	Mat src = imread("E:/cats.jpg", IMREAD_COLOR); // IMREAD_COLOR：加载为3通道彩色图像

	if (src.empty()) {
		printf("image is empty!!!");
		return -1;
	}

	// visit each pixel
	int height = src.rows;
	int width = src.cols;
	int ch = src.channels();
	for (int row = 0; row < height; row++) {
		for (int col = 0; col < width;col++) {
			if (ch == 3) {
				Vec3b pixel = src.at<Vec3b>(row, col);
				int blue = pixel[0];
				int green = pixel[1];
				int red = pixel[2];
				src.at<Vec3b>(row, col)[0] = 255 - blue;
				src.at<Vec3b>(row, col)[1] = 255 - green;
				src.at<Vec3b>(row, col)[2] = 255 - red;
			}
			if (ch == 1) {
				int pv = src.at<uchar>(row, col);
				src.at<uchar>(row, col) = (255 - pv);
			}
		}
	}


	imshow("src", src);
	waitKey(0);
	destroyAllWindows();
	return 0;
}

指针操作(实际工程中，多用指针，因为更加高效)

#include <opencv2/opencv.hpp>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char** argv) {

	Mat src = imread("E:/cats.jpg", IMREAD_COLOR); // IMREAD_COLOR：加载为3通道彩色图像

	if (src.empty()) {
		printf("image is empty!!!");
		return -1;
	}

	// visit each pixel
	int height = src.rows;
	int width = src.cols;
	int ch = src.channels();
	Mat result = Mat::zeros(src.size(), src.type());
	for (int row = 0; row < height; row++) {
		uchar* curr_row = src.ptr<uchar>(row);
		uchar* result_row = result.ptr<uchar>(row);
		for (int col = 0; col < width;col++) {
			if (ch == 3) {
				int blue = *curr_row++;
				int green = *curr_row++;
				int red = *curr_row++;

				*result_row++ = blue;
				*result_row++ = green;
				*result_row++ = red;

			}
			if (ch == 1) {
				int pv = *curr_row++;
				*result_row++ = pv;
			}
		}
	}


	imshow("result", result);
	waitKey(0);
	destroyAllWindows();
	return 0;
}