（4）OpenCV 4 学习之图像像素读写操作

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一、数组遍历（缺点：慢）

1、示例

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

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
	Mat src = imread("F:/Cvimage/test.png");

	if (src.empty())
	{
		printf("could not load image....\n");
		return -1;
	}
	namedWindow("input", WINDOW_AUTOSIZE);
	imshow("input", src);
	
	int height = src.rows;	//读图片高度
	int width  = src.cols;	//读取图片宽度
	int ch	   = src.channels();	//读取图片通道数 rgb：三通道  灰色图像：单通道  rgba：四通道，多一个透明度

	//数组读取图像像素
	for (int c = 0; c < ch; c++)
	{
		for (int row = 0; row < height; row++)
		{
			for (int col = 0; col < width; col++)
			{
				if (ch == 3)
				{
					Vec3b bgr = src.at<Vec3b>(row, col);
					bgr[0] = 255 - bgr[0];	//蓝  rgb 最大值为255，最终图像取反
					bgr[1] = 255 - bgr[1];	//绿
					bgr[2] = 255 - bgr[2];	//红

					src.at<Vec3b>(row, col) = bgr;
				}
				else if(ch == 1)
				{
					int gray = src.at<uchar>(row, col);
					src.at<uchar>(row, col) = 255 - gray;
				}
			}
		}
	}
	imshow("output", src);
	
	waitKey(0);

	return 0;
}

2、结果展示

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二、指针遍历

1、示例

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

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
	Mat src = imread("F:/Cvimage/test.png");

	if (src.empty())
	{
		printf("could not load image....\n");
		return -1;
	}
	namedWindow("input", WINDOW_AUTOSIZE);
	imshow("input", src);

	int height = src.rows;	//读图片高度
	int width  = src.cols;	//读取图片宽度
	int ch	   = src.channels();	//读取图片通道数 rgb：三通道  灰色图像：单通道  rgba：四通道，多一个透明度

	//指针读图图片像素
	Mat result = Mat::zeros(src.size(), src.type()); //创建一个空白图像
	int blue = 0, green = 0, red = 0;
	int gray;
	for (int c = 0; c < ch; c++)
	{
		for (int row = 0; row < height; row++)
		{
			uchar *curr_row   = src.ptr<uchar>(row); //获取这一行所有像素点的首地址
			uchar *result_row = result.ptr<uchar>(row);

			for (int col = 0; col < width; col++)
			{
				if (ch == 3)
				{
					//一个像素点有3个像素值，红、绿、蓝，
					blue  = *curr_row++;
					green = *curr_row++;
					red	  = *curr_row++;

					*result_row++ = blue;
					*result_row++ = green;
					*result_row++ = red;
				}
				else if(ch == 1)
				{
					gray = *curr_row++;
					*result_row++ = gray;
				}
			}
		}
	}
	imshow("reslut", result);

	waitKey(0);

	return 0;
}

2、结果展示