Valgrind Invalid read of size 4 (OpenCV)

Question

Here is my code:

template <typename TValue>
std::vector<cv::Point2i> GetPixelsWithValue(const cv::Mat& image, const TValue& value) {
    std::vector<cv::Point2i> pixels;
    cv::Size imageSize = image.size();
    for(int i = 0; i < imageSize.height; ++i) {
        for(int j = 0; j < imageSize.width; ++j) {
            if(image.at<TValue>(i, j) == value) {
                cv::Point2i pixel(j, i);
                pixels.push_back(pixel);
            }
        }
    }

    return pixels;
}

Valgrind is giving this error:

==10655== Conditional jump or move depends on uninitialised value(s)
==10655==    at 0x4E88517: GetPixelsWithValue<int>  (OpenCVExtensions.hpp:18)
==10655==    by 0x4E88517: CountPixelsWithValue<int> (OpenCVExtensions.hpp:31)
...
==10655==  Uninitialised value was created by a heap allocation
==10655==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10655==    by 0x117138EB: cv::fastMalloc(unsigned long) (alloc.cpp:64)
==10655==    by 0x1184F795: cv::StdMatAllocator::allocate(int, int const*, int, void*, unsigned long*, int, cv::UMatUsageFlags) const (matrix.cpp:192)
==10655==    by 0x118507BE: cv::Mat::create(int, int const*, int) (matrix.cpp:426)
==10655==    by 0x4E9BA31: create (mat.inl.hpp:684)
==10655==    by 0x4E9BA31: Mat (mat.inl.hpp:351)
==10655==    by 0x4E9BA31: cv::Mat 
....    
==10655== Invalid read of size 4
==10655==    at 0x4E88510: GetPixelsWithValue<int> (OpenCVExtensions.hpp:18)
....
==10655==  Address 0x23201c92 is 127,346 bytes inside a block of size 127,347 alloc'd
==10655==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10655==    by 0x117138EB: cv::fastMalloc(unsigned long) (alloc.cpp:64)
 ==10655==    by 0x1184F795: cv::StdMatAllocator::allocate(int, int const*, int, void*, unsigned long*, int, cv::UMatUsageFlags) const (matrix.cpp:192)
==10655==    by 0x118507BE: cv::Mat::create(int, int const*, int) (matrix.cpp:426)
==10655==    by 0x4E9BA31: create (mat.inl.hpp:684)
==10655==    by 0x4E9BA31: Mat (mat.inl.hpp:351)

I found these and some more:

Why am I getting memory errors when accessing this matrix in OpenCV?

Invalid write size of 4 with matrix class (using valgrind)

However I failed to understand why I am getting the error. Could this be an error internally coming from OpenCV?

Presumably the image you passed in was bogus to begin with? – Kerrek SB Feb 20 '17 at 23:22 — Kerrek SB, Feb 20 '17 at 23:22

score 0 · Accepted Answer · answered Feb 21 '17 at 17:28

Found the issue. As @Kerrek SB pointed out the image was the problem. Below is a more complete example. It seems like the uninitialized value errors were, well, due to trying to use uninitialized matrices. I might also have out of bounds indices which are causing the invalid read errors.

#include "opencv2/highgui/highgui.hpp"
#include <iostream>

using namespace std;
using namespace cv;

std::vector<cv::Point2i> GetPixelsWithValue(const cv::Mat1b& image, const unsigned char& value) {
    std::vector<cv::Point2i> pixels;
    cv::Size imageSize = image.size();
    for(int i = 0; i < imageSize.height; ++i) {
        for(int j = 0; j < imageSize.width; ++j) {
            if(image.at<unsigned char>(i, j) == value) {
                cv::Point2i pixel(j, i);
                pixels.push_back(pixel);
            }
        }
    }

    return pixels;
}

int main()
{

    cv::Mat1b image(10, 12);
    image.setTo(0); //enable this and all the uninitialized value errors go away

    image(0,1) = 63;
    image(1,3) = 63;
    image(3,5) = 63;
    image(4,7) = 63;
    image(5,9) = 63;
//    image(10,12) = 63; //causes invalid write error

    std::vector<cv::Point2i> vec = GetPixelsWithValue(image, static_cast<unsigned char>(63));

    std::cout << image(10,12) << std::endl; //bad access. causes invalid read error only
    std::cout << vec.size() << std::endl;

    return 0;
}

Valgrind Invalid read of size 4 (OpenCV)

1 Answers1