Image processing : luminance weighted 2 - c++

Question

I would like to weigh values of luminance on a new image.
I have an image (5px.jpg) of 5 pixels with these luminance :50,100,150,200,250.
I have a vector of coefficient.
I created a new Mat Z which combine luminance of 5px.jpg and the coefficient.
So, my first value of luminance is 50 (lum[0]=50) and I want it to be applied on the 5.1 (coef[0]=5.1) first pixel of my matrix. To do that, I need to weight the 6th pixel with the first and the second value of luminance. In my case,the luminance of my 6th pixel will be 95 because (0.1*50)+(0.9*100)=95
And so on...
But I do not know why my code does not works.
I had already asked a similar question for a vector here and now, I'm try to adapt to an image.
My picture in input :
My output :
#define MPI 3.14159265358979323846264338327950288419716939937510
#define RAD2DEG (180./MPI)
#include "opencv2/core/core.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <opencv2/opencv.hpp>
#include <iostream>
#include <cmath>
#include <math.h>
#include <string.h>
using namespace cv;
using namespace std;
int main()
{
Mat image = imread("5px.jpg", 1);
if (image.empty())
{
cout << "Couldn't load " << image << endl;
}
else
{
cout << "Image upload, go" << endl;
}
namedWindow("ImageIn", CV_WINDOW_AUTOSIZE);
imshow("ImageIn", image);
Mat imgGrayScale;
cvtColor(image, imgGrayScale, CV_BGR2GRAY);
float *deltaP = new float[imgGrayScale.cols];
float *angle = new float[imgGrayScale.cols];
float *coeff = new float[imgGrayScale.cols];
int col;
for (col = 0; col < imgGrayScale.cols; ++col)
{
//cout << "position x = " << col << endl;
deltaP[col] = imgGrayScale.at<uchar>(0, col);
//cout << "luminance = " << deltaP[col] << endl;
angle[col] = acos(deltaP[col] / 255);
//cout << "angle =" << angle[col] << endl;
coeff[col] = (1 / cos(angle[col]));
cout << "coeff = " << coeff[col] << endl;
}
int width = imgGrayScale.size().width;
int height = imgGrayScale.size().height;
int width2 = width * 5;
int idx_coef = 0;
Mat Z = Mat::zeros(height, width2, CV_8UC1);
//for (int r = 0; r < imgGrayScale.rows; r++)
//{
//cout << "Saut de ligne " << endl << endl << endl;
for (int t = 0; t < imgGrayScale.cols; t++)
{
//cout << "Saut de colonne " << endl;
// Attribue le coeff à une variable
int c = int(coeff[idx_coef]);
//cout << "x" << t << endl;
for (int i = 0; i < c; ++i)
{
Z.at<uchar>(0, c) = imgGrayScale.at<uchar>(0, t);
}
float alpha = fmod(coeff[idx_coef], 1.f);
float beta = 1.f - alpha;
Z.at<uchar>(0, c + 1) = (alpha * imgGrayScale.at<uchar>(0, t) + beta * imgGrayScale.at<uchar>(0, t + 1));
idx_coef++;
coeff[idx_coef] = coeff[idx_coef] - beta;
if (idx_coef >= width - 1)
{
int cc = int(coeff[idx_coef]);
for (int i = 0; i < cc; ++i)
{
Z.at<uchar>(0, c) = imgGrayScale.at<uchar>(0, t);
}
idx_coef = 0;
break;
}
}
//}
namedWindow("m", CV_WINDOW_AUTOSIZE);
imshow("m", Z);
imwrite("lumianacetest.jpg", Z);
int t = waitKey();
if ((char)t == 27)
return 0;
}

Answer 1

You messed up with the indices while accessing the matrix Z. You shoudn't access Z at column c, but you need access the current column (as a vector::push_back would do). So you can keep the current index column in a variable, here idx_z, and increment it every time you access Z
Here your Z is CV_8U, so you lose accuracy since your values are float. You can create Z as CV_32F, and if you need to store values in CV_8U format to save the image, you can convert to CV_8U later, eventually.
The last columns of Z won't be set to any value (so I initialized them with value 0). If you need them to have the last value as in the imgGrayScale, just decomment the relevant part of the code.
Here the code:
#define MPI 3.14159265358979323846264338327950288419716939937510
#define RAD2DEG (180./MPI)
#include <opencv2\opencv.hpp>
#include <vector>
using namespace cv;
using namespace std;
int main()
{
Mat1b imgGrayScale = (Mat1b(2, 5) << 50, 100, 150, 200, 250,
50, 100, 150, 200, 250);
vector<float> deltaP(imgGrayScale.cols);
vector<float> angle(imgGrayScale.cols);
vector<float> coeff(imgGrayScale.cols);
int col;
for (col = 0; col < imgGrayScale.cols; ++col)
{
//cout << "position x = " << col << endl;
deltaP[col] = imgGrayScale.at<uchar>(0, col);
//cout << "luminance = " << deltaP[col] << endl;
angle[col] = acos(deltaP[col] / 255);
//cout << "angle =" << angle[col] << endl;
coeff[col] = (1 / cos(angle[col]));
cout << "coeff = " << coeff[col] << endl;
}
int width = imgGrayScale.size().width;
int height = imgGrayScale.size().height;
int width2 = width * 5;
Mat1f Z(height, width2, 0.f);
for (int r = 0; r < imgGrayScale.rows; r++)
{
int idx_lum = 0;
int idx_coef = 0;
int idx_z = 0;
vector<float> coef = coeff;
// Set all values in Z to the last value in imgGrayScale
Z.row(r) = imgGrayScale(r, imgGrayScale.cols-1);
while (true)
{
int c = int(coef[idx_coef]);
for (int i = 0; i < c; ++i)
{
Z(r, idx_z++) = imgGrayScale(r, idx_lum);
}
float alpha = fmod(coef[idx_coef], 1.f);
float beta = 1.f - alpha;
Z(r, idx_z++) = (alpha * imgGrayScale(r, idx_lum) + beta * imgGrayScale(r, idx_lum + 1));
idx_coef++;
idx_lum++;
coef[idx_coef] = coef[idx_coef] - beta;
if (idx_lum >= imgGrayScale.cols - 1 || idx_coef >= coef.size() - 1)
{
int cc = int(coef[idx_coef]);
for (int i = 0; i < cc; ++i)
{
Z(r, idx_z++) = imgGrayScale(r, idx_lum);
}
idx_coef = 0;
break;
}
}
}
Mat1b ZZ;
Z.convertTo(ZZ, CV_8U);
cout << "Float values:" << endl;
cout << Z << endl << endl;
cout << "Uchar values:" << endl;
cout << ZZ << endl << endl;
namedWindow("m", CV_WINDOW_AUTOSIZE);
imshow("m", Z);
imwrite("lumianacetest.png", ZZ);
waitKey();
return 0;
}