[Learning OpenCV4] Image Channel Splitting, Merging, and Mixing Methods (C++)

I. Splitting Image Channels

void split(
	const cv::Mat& image, //输入图像
	vector<Mat>& mv // 输出的多通道序列（n个单通道序列）
);

  The output multi-channel sequence is typically stored using std::vector<Mat> mv;, where mv[0] , mv[1], mv[2], correspond to the three BGR channels respectively.      Example code:

void MyDemo::channels_Demo(Mat& image) {
	std::vector<Mat> mv;
	split(image, mv);
	imshow("Blue Channel", mv[0]);
	imshow("Green Channel", mv[1]);
	imshow("Red Channel", mv[2]);
}

II. Merging Channels

  However, what is displayed now is essentially three single-channel images—in other words, three grayscale images. To restore intuitive color to the three images, you need to use the channel merging method described below.

  Channel merging uses the merge() function.

void merge(
	const vector<cv::Mat>& mv, // 输入的多通道序列(n个单通道序列)
	cv::OutputArray dst // 输出图像，包含mv
);

  According to the definition of merge(), we only need to control the three values in the input multi-channel array mv[] to merge the channels.

  Example code:

void MyDemo::channels_Demo(Mat& image) {
	std::vector<Mat> mv;
	split(image, mv);
	
	Mat m1,m2,m3;
	mv[1] = 0;
	mv[2] = 0;
	merge(mv, m1);
	imshow("Blue Channel", m1);

	split(image, mv);
	mv[0] = 0;
	mv[2] = 0;
	merge(mv, m2);
	imshow("Green Channel", m2);

	split(image, mv);
	mv[0] = 0;
	mv[1] = 0;
	merge(mv, m3);
	imshow("Red Channel", m3);
}

  We already know how to extract the three channels of an image, so we can combine them in any way we want and merge them into the image we need.

III. Mixing Channels

  Channel mixing also rearranges the three channels in any order

C++: void mixChannels(const Mat*src, size_t nsrcs, Mat* dst, size_t ndsts, const int* fromTo, size_t npairs)

Parameter	Role
src	Input matrix
nsrcs	Number of input matrices
dst	Output matrix
ndsts	Number of output matrices
fromTo	Index pair vector

void MyDemo::channels_Demo(Mat& image) {
	Mat dst = Mat::zeros(image.size(), image.type());
	int ft[] = { 0,2,1,1,2,0 };//互换1、3通道
	mixChannels(&image,1, &dst,1, ft,3);
	imshow("Mix", dst);
}