Calculate RGB Image Matrix with several custom matrices in C++ OpenCV

Question

Helllo, I'm newbie in C++ OpenCV programming. I have one colour image, and i want that image multiplied with several matrices (masking). This is the outline of code:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
using namespace std;
using namespace cv;
char* hai;
int main()
{

hai = "c:/Dalton/grayscale.jpg";
Mat im = imread(hai);
Mat Result;
const int nChannels = im.channels(); //get channel sum from the image (it should be 3 channel,because RGB)
Result.create(im.size(), im.type()); //create new mat (for the result) which have same size and type with first mat
double rgb2lms[3][3] = { 17.8824, 43.5161, 4.11935,
    3.45565, 27.1554, 3.86714,
    0.0299566, 0.184309, 1.46709 };
double lms2lmsp[3][3] = { 0, 2.02344, -2.52581,
                        0, 1, 0,
                        0, 0, 1 };
if (im.empty())
{
    cout << "Cannot load image!" << endl;
    return -1;
}
//access pixel
for (int i = 0; i < im.rows; i++)
{
    for (int j = 0; j < im.cols; j++)
    {
        for (int k = 0; k < nChannels; k++)
        {

            //main program
            //calculating matrix    
            //i want calculate im(RGB matrix) multiply with rgb2lms
            //after that, the result is multiplied again with lms2lmsp matrix
        }
    }
}   
imshow("Image", im);
imshow("Image Result", Result);
waitKey(0);

}

How i can multiply this RGB mat matrix with another matrix? Should i access every pixel? I want to multiplied original image with rgb2lms matrix and then the result multiplied again with lms2lmsp matrix. Anyone can help me? Thanks

Do you not know how to do the math? Are you asking if there's a pre-existing library that does this? Are you having performance problems and are looking for the most efficient way to do this? It's a bit unclear what you're wanting us to help you with. — Jeff B, Dec 22 '14 at 13:47
@JeffBridgman clearly, i want to multiply RGB matrix with several matrices. Example: A=RGB*rgb2lms and then C=A*lms2lmsp. I don't have any idea to do that in c++ with 3 channels matrix. — Mahendra Sunt Servanda, Dec 23 '14 at 00:54

Daniel · Accepted Answer · 2014-12-23T10:31:52.300

1

If you are asking how to multiply matrices, OpenCV API does it:

Mat::mul Performs an element-wise multiplication or division of two matrices.

EDIT:

This tutorial explains how to apply a mask matrix on an image. I think that's what you are looking for..

http://docs.opencv.org/doc/tutorials/core/mat-mask-operations/mat-mask-operations.html

edited Dec 23 '14 at 10:31

answered Dec 22 '14 at 14:01

Daniel

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But i still confuse how to multipy RGB 3 channels image matrix with 3x3 matrix. Should i use ordinary matrix multiplication (A*B)? Or i must use element-wise multiplication?? – Mahendra Sunt Servanda Dec 23 '14 at 02:17
@MahendraSuntServanda I hope the tutorial helps you. – Daniel Dec 23 '14 at 10:33

Calculate RGB Image Matrix with several custom matrices in C++ OpenCV

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