# 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 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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