Opencv入门——读写图像、读写像素、修改像素值

读写图像

  1. imread()可以指定加载图像为灰度图或者RGB格式
  2. imwrite()保存图像文件,类型由扩展名决定

读写像素

读写一个GRAY像素点的像素值(CV_8UC1)

gray = gray_img.at(row, col);

读取一个RGB图像的像素点的像素值

int b = img.at(row, col)[0];
int g = img.at(row, col)[1];
int r = img.at(row, col)[2];

或者

float b = img.at(row, col)[0];
float g = img.at(row, col)[1];
float r = img.at(row, col)[2];

Mat dst;

dst.at(row, col)[0] = 255 - b;//反写
dst.at(row, col)[1] = 255 - g;
dst.at(row, col)[2] = 255 - r;

修改像素值

灰度图像

img.at(y,x) = 200;

RGB三通道图像

int b = img.at(y,x)[0] = 56;//blue
int g = img.at(y,x)[1] = 124;//green
int r = img.at(y,x)[2] = 220;//red

空白图像赋值

img=Scalar(0);

ROI选择

Rect r(10, 10, 100, 100);

Mat smallImg = img(r);

Vec3b与Vec3f

Vec3b对应三通道的顺序是bluegreenreduchar类型数据

Vec3f对应三通道的float类型数据

CV_8UC1转换到CV32F1实现如下:

src.convertTo(dst, CV_32F);

#include
#include

using namespace cv;
using namespace std;

int main()
{
	Mat img, gray_img, dst;
	img = imread("D:\\OpenCV\\images\\4.jpg");

	if (img.empty())
	{
		cout << "image loading failed..." << endl;
		return -1;
	}
	namedWindow("input", WINDOW_AUTOSIZE);
	imshow("input", img);

	cvtColor(img, gray_img, COLOR_BGR2GRAY);
	//imshow("gray_img", gray_img);
	
	int height = gray_img.rows;
	int weight = gray_img.cols;
	
	int nc = gray_img.channels();
	//printf("the channel of this image is %d\n", nc);

	if (nc == 1)//单通道
	{
		for (int row = 0; row < height; row++)
		{
			for (int col = 0; col < weight; col++)
			{
				int gray = gray_img.at(row, col);
				gray_img.at(row, col) = 255 - gray;
			}
		}
		imshow("output", gray_img);
	}
	else
	if (nc == 3)//三通道
	{
		dst.create(img.size(), img.type());
		for (int row = 0; row < height; row++) 
		{
			for (int col = 0; col < weight; col++)
			{
				int b = img.at(row, col)[0];//读取三个通道的像素值
				int g = img.at(row, col)[1];
				int r = img.at(row, col)[2];
				
				dst.at(row, col)[0] = 255 - b;//反射操作
				dst.at(row, col)[1] = 255 - g;
				dst.at(row, col)[2] = 255 - r;

				gray_img.at(row, col) = min(r, min(g, b));
			}
		}
		imshow("gray_img", gray_img);
		imshow("dst", dst);
		//imwrite("D:\\OpenCV\\images\\gray_img.jpg", gray_img);
		//imwrite("D:\\OpenCV\\images\\dst.jpg", dst);
	}
	//bitwise_not(img, dst);
	waitKey(0);
	return 0;
}

来几张效果图

Opencv入门——读写图像、读写像素、修改像素值_第1张图片 原图
Opencv入门——读写图像、读写像素、修改像素值_第2张图片 灰度图像素取反

 

Opencv入门——读写图像、读写像素、修改像素值_第3张图片 按每个像素点三通道灰度值最小的规则得到的图像

 

Opencv入门——读写图像、读写像素、修改像素值_第4张图片 三通道像素取反后的图像

 

有点吓人是吧,哈哈哈

 

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