CODEWITHSUNDEEP
c++opencvimage-processingrgb
mohammad
mohammad

Reputation: 2212

C++:openCV error

hi all i am trying to get the RGB for a pixel in an image using C++ openCV 2.4.5

but i get this error when i compile .

it loads the image will but the exception arise when i am trying to get the RGB for a pixel

can any one help me please ?

enter image description here

the following code loads an image and find the RGB for a pixel at index 25,4
my code is :

 #include <opencv2/core/core.hpp>
    #include <opencv2/highgui/highgui.hpp>
    #include <opencv2/imgproc/imgproc.hpp>
    #include <opencv/cv.h>
    #include <opencv/highgui.h>
    #include <iostream>
    using namespace std;
    using namespace cv;
    int main()
    {
        int x;
        Mat input = imread("C:/red.jpg");
        if (input.empty())
            {
                std::cout << "!!! Failed imread(): image not found" << std::endl;
                cin>>x;
                return 0;
                // don't let the execution continue, else imshow() will crash.
            }
        imshow("input", input);
         Vec3f pixel = input.at<Vec3f>(25, 40);
         if( !pixel[0])
         {
             std::cout << "!!! Failed pixel(): image not found" << std::endl;
                cin>>x;
                return 0;
         }
            int b = pixel[0];
            int g = pixel[1];
            int r = pixel[2];
        cout<<b;
        cout <<" ";
        cout<<r;
        cout <<" ";
        cout <<g;
        cin>>b;

        /*




        // detect squares after filtering...
        */
        return 0;
    }

Upvotes: 0

Views: 1757

Answers (2)

Arsalan
Arsalan

Reputation: 1

you should use :

Mat input = imread("C://red.jpg");

instead of :

Mat input = imread("C:/red.jpg");

Upvotes: 0

Alexey
Alexey

Reputation: 5978

You image is probably of type CV_8UC3, which means the value of a pixel is stored as 3-channel 8-bit uchar. In

Vec3f pixel = input.at<Vec3f>(25, 40);

you are trying to access pixel values as floats, since in OpenCV Vec3f is defined as typedef Vec<float, 3> Vec3f;. This causes your program to crush. Instead it should be: 

Vec3b pixel = input.at<Vec3b>(25, 40);

In OpenCV Vec3b is defined as typedef Vec<uchar, 3> Vec3b;, which is what you want.

Here's the documentation for cv:: Vec data type.

EDIT You can output the pixel data simply with

cout << pixel << endl;

or like this:

printf("[%u, %u, %u]", pixel[0], pixel[1], pixel[2]);

or like this:

int b = static_cast<int>(pixel[0]);
int g = static_cast<int>(pixel[1]);
int r = static_cast<int>(pixel[2]);
cout<< "[" << b <<", " << g << ", " << r << "]" << endl;

Upvotes: 3

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