OpenCV4（4）-图像像素读写操作（C++，Python，JS） - 入门 - OpenCV - 人工智能 | Aayu Yain = 学无止境 = 世界上大部分事，都没太大意义。真理与热爱除外

# 环境

Python：3.6.5 OpenCV 4.1.2
C++：OpenCV 4.1.2
JS：OpenCV 4.5.0

环境搭建可参考：B 站视频

# 知识点

C++ 中的像素遍历与访问

数组遍历
指针遍历

Python 中的像素遍历与访问

数组遍历

# C++ 代码

#ifndef DAY04
#define DAY04

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

using namespace std;
using namespace cv;

void day04() {

	Mat src = imread("E:\\_Image\\OpenCVTest\\girl.jpg");

	if (src.empty()) {
		cout << "could not load image.." << endl;
		return;
	}

	// 直接读取图像像素
	int height = src.rows;
	int width = src.cols;
	int ch = src.channels();
	for (int row = 0; row < height; row++) {
		// 像素取反
		for (int col = 0; col < width; col++) {
			if (ch == 3) {
				Vec3b bgr = src.at<Vec3b>(row, col);
				bgr[0] = 255 - bgr[0];
				bgr[1] = 255 - bgr[1];
				bgr[2] = 255 - bgr[2];
				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);

	// 指针读取
	Mat result = Mat::zeros(src.size(), src.type());
	int blue = 0, green = 0, red = 0;
	int gray;
	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) {
				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("result", result);

	waitKey(0);
}

#endif // !DAY04

# Python 代码

	import cv2 as cv
	import numpy as np

	# 查看版本
	print(cv.__version__)

	# 读取图像
	src = cv.imread("E:/_Image/OpenCVTest/girl.jpg")

	# 查看属性
	h, w, ch = src.shape
	print("h, w, ch", h, w, ch)

	# 像素取反
	for row in range(h):
	for col in range(w):
	b, g, r = src[row, col]
	b = 255 - b
	g = 255 - g
	r = 255 - r
	src[row, col] = [b, g, r]
	cv.imshow("output", src)

	# 等待键盘输入
	cv.waitKey()

	# 释放内存
	cv.destroyAllWindows()

# JS 代码

	<template>
	<div>
	<p>图像像素读写</p>
	<p id="status">OpenCV.js is loading...</p>
	<div class="inputoutput">
	<img id="imageSrc" alt="No Image" />
	<div class="caption">imageSrc <input type="file" id="fileInput" name="file" /></div>
	</div>
	<div class="inputoutput">
	<canvas id="canvasOutput"></canvas>
	<div class="caption">canvasOutput</div>
	</div>
	</div>
	</template>

	<script>
	export default {
	name: "day04",
	mounted() {
	this.init();
	},
	methods: {
	init() {
	setTimeout(() => {
	if (window.cv) {
	this.onOpenCvReady(window.cv);
	} else {
	this.init();
	}
	}, 500);
	},
	onOpenCvReady(cv) {
	document.getElementById("status").innerHTML = "OpenCV.js is ready.";
	let imgElement = document.getElementById("imageSrc");
	let inputElement = document.getElementById("fileInput");
	inputElement.addEventListener(
	"change",
	e => {
	imgElement.src = URL.createObjectURL(e.target.files[0]);
	},
	false
	);
	imgElement.onload = function() {
	let src = cv.imread(imgElement);

	// 1. data 取值，获取适用于连续 Mat，需用 isContinous () 检测是否连续
	// 取（3，4）这个位置的像素
	let row = 3;
	let col = 4;
	let R, G, B, A;
	if (src.isContinuous()) {
	R = src.data[row * src.cols * src.channels() + col * src.channels()];
	G =
	src.data[
	row * src.cols * src.channels() + col * src.channels() + 1
	];
	B =
	src.data[
	row * src.cols * src.channels() + col * src.channels() + 2
	];
	A =
	src.data[
	row * src.cols * src.channels() + col * src.channels() + 3
	];
	console.log(R, G, B, A);
	}

	// 2. at 限制：不能修改
	R = src.ucharAt(row, col * src.channels());
	G = src.ucharAt(row, col * src.channels() + 1);
	B = src.ucharAt(row, col * src.channels() + 2);
	A = src.ucharAt(row, col * src.channels() + 3);
	console.log(R, G, B, A);

	// 3. ptr 一般使用这个，简单方便
	let pixel = src.ucharPtr(row, col);
	R = pixel[0];
	G = pixel[1];
	B = pixel[2];
	A = pixel[3];
	console.log(R, G, B, A);
	// 修改
	pixel[0] = 0;
	pixel[1] = 0;
	pixel[2] = 0;
	pixel[3] = 255;
	console.log(src.ucharPtr(row, col));
	cv.imshow("canvasOutput", src);

	src.delete();
	};
	}
	}
	};
	</script>

	<style lang="scss" scoped>
	</style>

官方文档链接：https://docs.opencv.org/4.5.0/de/d06/tutorial_js_basic_ops.html