Lomography effect

In this section, we are going to create another image effect, which is a photograph effect that is very common in different mobile applications, such as Google Camera or Instagram. We are going to discover how to use a look-up table (LUT). We will go through LUTs later in this same section. We are going to learn how to add an over image, in this case a dark halo, to create our desired effect. The function that implements this effect is the lomoCallback callback and it has the following code:

void lomoCallback(int state, void* userData) 
{ 
    Mat result; 
 
    const double exponential_e = std::exp(1.0); 
    // Create Look-up table for color curve effect 
    Mat lut(1, 256, CV_8UC1); 
    for (int i=0; i<256; i++) 
    { 
        float x= (float)i/256.0;  
        lut.at<uchar>(i)= cvRound( 256 * (1/(1 + pow(exponential_e, -((x-0.5)/0.1)) )) ); 
...