OpenCV3 C++ 图像的一些简单变换

主要包括C++图像的高斯模糊、Canny边缘检测、降采样、读写像素值的实现

#include "opencv2/opencv.hpp"

using namespace cv;
using namespace std;

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

	Mat img = imread("F:/test/apple.jpg"); // 定义一个Mat（Matrix）容器用于存储图像
	if (img.empty()) return -1;
	namedWindow("imgRead", WINDOW_AUTOSIZE);  // WINDOW_FREERATIO可手动调节窗口大小


	//高斯模糊
	Mat out;
	GaussianBlur(img, out, Size(5, 5), 3, 3);
	imshow("GaussianProcess2", out);

	//色彩空间转换
	Mat gray, hsv;
	cvtColor(out, hsv, COLOR_BGR2HSV);
	cvtColor(out, gray, COLOR_BGR2GRAY);
	imshow("HSV", hsv);
	imshow("GRAY", gray);
	
	//高斯平滑处理后的Canny边缘检测
	Mat cny;
	Canny(gray, cny, 10, 100, 3, true);
	imshow("Canny", cny);
	//未经高斯平滑的Canny边缘检测
	Mat gray2, cny2;
	cvtColor(img, gray2, COLOR_BGR2GRAY);
	Canny(gray2, cny2, 10, 100, 3, true);
	imshow("Canny2", cny2);

	//降采样
	Mat down1, down2;
	pyrDown(img, down1);
	imshow("down1", down1);
	pyrDown(down1, down2);
	imshow("down2", down2);

	//读取指定坐标处的像素值
	int x = 16, y = 32;
	Vec3b intensity = img.at< Vec3b >(y, x);

	uchar blue = intensity[0];
	uchar green = intensity[1];
	uchar red = intensity[2];

	cout << "At (x,y) = (" << x << "," << y << "):(blue, green, red) = (" << (unsigned int)blue << "," << (unsigned int)green << "," << (unsigned int)red << ")" << endl;
	Mat gry;
	cvtColor(img, gry, COLOR_BGR2GRAY);
	cout << "Gray pixel there is:" << (unsigned int)gry.at(y, x) << endl;

	x /= 4, y /= 4;
	cout << "Pyramid2 pixel there is " << (unsigned int)down2.at(y, x) << endl;

	//Set the gray pixel there to 128
	gry.at(x, y) = 128;
	cout << "Gray reset pixel there is:" << (unsigned int)gry.at(x, y) << endl;


	imshow("imgRead", img);
	waitKey(0);
	destroyAllWindows();
}

高斯模糊函数：GaussianBlur()。5个参数分别为：输入图像、输出图像、高斯核的大小、高斯核函数在X方向的的标准偏差、高斯核函数在Y方向的的标准偏差。

色彩空间转换函数：cvtColor()。3个参数分别为：输入图像、输出图像、色彩空间转换方式。

Canny边缘检测函数：Canny()。6个参数分别为：输入图像（必须是单通道）、输出图像、第一个阈值、第二个阈值、Sobel 算子内核大小，最后一个参数是一个布尔值，如果为真，则使用更精确的L2范数进行计算（即两个方向的倒数的平方和再开放），否则使用L1范数（直接将两个方向导数的绝对值相加。而在两个阈值中，第一个阈值用来控制边缘连接，第二个阈值用来控制强边缘的初始分割。

降采样：pyrDown()。每次降采样都使图像的宽高分别缩小一半。

读取像素值部分：

定义一个类型为uchar长度为3的数组，at定位到（y, x）处的像素：

Vec3b intensity = img.at< Vec3b >(y, x);

 分别取出对应像素中三个通道的值：

uchar blue = intensity[0];
uchar green = intensity[1];
uchar red = intensity[2];

由于返回的使uchar类型的值，在cout输出时需要强制转换类型：

cout << "At (x,y) = (" << x << "," << y << "):(blue, green, red) = (" << (unsigned int)blue << "," << (unsigned int)green << "," << (unsigned int)red << ")" << endl;

结果图如下：

原图和高斯平滑后对比：

 色彩空间转换后：

 Canny边缘检测：高斯平滑后的边缘检测对比未经高斯平滑的边缘检测结果

两次降采样：