作者：翟天保Steven
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实现原理

       怀旧色可以通过调整RGB三通道数值实现，具体公式：

功能函数代码

// 怀旧色
cv::Mat Nostalgic(cv::Mat src)
{
	CV_Assert(src.channels() == 3);
	int row = src.rows;
	int col = src.cols;
	cv::Mat temp = src.clone();
	for (int i = 0; i < row; ++i)
	{
		uchar *s = src.ptr<uchar>(i);
		uchar *t = temp.ptr<uchar>(i);
		for (int j = 0; j < col; ++j)
		{
			int B = s[3 * j];
			int G = s[3 * j + 1];
			int R = s[3 * j + 2];
			// 怀旧调色
			float newB = 0.272f*R + 0.534f*G + 0.131f*B;
			float newG = 0.349f*R + 0.686f*G + 0.168f*B;
			float newR = 0.393f*R + 0.769f*G + 0.189f*B;
			if (newB < 0)
				newB = 0;
			if (newB > 255)
				newB = 255;
			if (newG < 0)
				newG = 0;
			if (newG > 255)
				newG = 255;
			if (newR < 0)
				newR = 0;
			if (newR > 255)
				newR = 255;
			t[3 * j] = (uchar)newB;
			t[3 * j + 1] = (uchar)newG;
			t[3 * j + 2] = (uchar)newR;
		}
	}
	return temp;
}

C++测试代码

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

using namespace std;
using namespace cv;

cv::Mat Nostalgic(cv::Mat src);

int main()
{
	cv::Mat src = imread("test2.jpg");
	cv::Mat result1 = Nostalgic(src);

    cv::Mat gray;
	cvtColor(src, gray, COLOR_BGR2GRAY);

	cv::imshow("original", src);
    cv::imshow("gray", gray);
	cv::imshow("result", result);
	waitKey(0);
	return 0;
}

// 怀旧色
cv::Mat Nostalgic(cv::Mat src)
{
	CV_Assert(src.channels() == 3);
	int row = src.rows;
	int col = src.cols;
	cv::Mat temp = src.clone();
	for (int i = 0; i < row; ++i)
	{
		uchar *s = src.ptr<uchar>(i);
		uchar *t = temp.ptr<uchar>(i);
		for (int j = 0; j < col; ++j)
		{
			int B = s[3 * j];
			int G = s[3 * j + 1];
			int R = s[3 * j + 2];
			// 怀旧调色
			float newB = 0.272f*R + 0.534f*G + 0.131f*B;
			float newG = 0.349f*R + 0.686f*G + 0.168f*B;
			float newR = 0.393f*R + 0.769f*G + 0.189f*B;
			if (newB < 0)
				newB = 0;
			if (newB > 255)
				newB = 255;
			if (newG < 0)
				newG = 0;
			if (newG > 255)
				newG = 255;
			if (newR < 0)
				newR = 0;
			if (newR > 255)
				newR = 255;
			t[3 * j] = (uchar)newB;
			t[3 * j + 1] = (uchar)newG;
			t[3 * j + 2] = (uchar)newR;
		}
	}
	return temp;
}

测试效果

       怀旧色滤镜完成，与灰度图相比，有种古典萧瑟的感觉~

       如果函数有什么可以改进完善的地方，非常欢迎大家指出，一同进步何乐而不为呢~

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