adding float openCV3.0 - c++

Question

I actually have a problem on openCV3.0.
I used 12 gabor filters(12 differents orientation) on 1 image and stocked them.
Now I want to add all those images and then divide by 12 each value to obtain the mean of the 12 filters.
Because those image are RGB, I have to work on each channel separatly.
The problem is : when I add all the values, I obtain values > 12 while all the values are between 0 and 1.
The part of the code bugged :
for (i = 0; i < gaborV.size(); ++i) { //gaborV contain the 12 gabor filters
std::vector<cv::Mat> vec_split; //I split because of the 3 channels
cv::split(gaborV[i], vec_split);
for (int k = 0; k < imgCol.rows; ++k) {
for (int j = 0; j < imgCol.cols; ++j) {
if (k == 1 && j == 1)
std::cout << mat_X.at<float>(k, j) << " " << vec_split[0].at<float>(k, j) << std::endl;
mat_X.at<float>(k, j) += vec_split[0].at<float>(k, j);
mat_Y.at<float>(k, j) += vec_split[1].at<float>(k, j);
mat_Z.at<float>(k, j) += vec_split[2].at<float>(k, j);
}
}
}
and mat_X, mat_Y and mat_Z are created as follow :
mat_X = mat_Y = mat_Z = cv::Mat(cvSize(imgColNormalize.cols, imgColNormalize.rows), CV_32FC1, cvScalar(0.));
As I said, all values in vec_split are between 0 and 1, but when I'm out of the loop, mat_X, mat_Y and mat_Z contain values > 12..
The output of the cout I used :
0 0.507358
1.54751 0.496143
3.00963 0.528832
4.53887 0.465426
... and at the end I have 15.9459
And i don't understand since 0 + 0.507358 != 1.54751; 1.54751 + 0.496143 != 3.00963 ...
Do someone understand the problem?
Thanks for all!

Answer 1

I think the problem is here:
mat_X = mat_Y = mat_Z = cv::Mat(cvSize(imgColNormalize.cols,
imgColNormalize.rows), CV_32FC1, cvScalar(0.));
The way you initialise these arrays results in all three cv::Mat objects referencing the same data. Only one Mat is created and so your code increments the values in this array three times.
For info, OpenCV uses a reference counting mechanism with cv::Mat and the assignment operator simply creates a new reference to existing data. If you wanted to create a genuine deep-copy of a cv::Mat, you would need to use cv::Mat::clone().
So, instead, initialise like so:
mat_X = cv::Mat(cvSize(imgColNormalize.cols, imgColNormalize.rows), CV_32FC1, cvScalar(0.));
mat_Y = cv::Mat(cvSize(imgColNormalize.cols, imgColNormalize.rows), CV_32FC1, cvScalar(0.));
mat_Z = cv::Mat(cvSize(imgColNormalize.cols, imgColNormalize.rows), CV_32FC1, cvScalar(0.));
An excerpt from the documentation copied below for posterity: