SIGILL in mcc

[vrabaud]

System information (version)

• OpenCV => 4.6.0 (HEAD)
• Operating System / Platform => Linux
• Compiler => clang 13

Detailed description

Some found corners lead to inf being computed which screws up the code.

To be precise: both v1 and v2 end up containing -inf which leads to a SIGILL at

opencv_contrib/modules/mcc/src/checker_detector.cpp

Line 1109 in 9d0a451

float asp = (float)(norm(v2) / norm(v1));

because you are computing inf/inf (if you have throwing NaNs).

A solution could be to add if (Vcart.z == 0) Vcart.z += 0.0001; after

opencv_contrib/modules/mcc/src/bound_min.cpp

Line 168 in 9d0a451

Vcart = lines[i].cross(lines[j]);

I am not familiar with the code to know whether it makes sense though.

Steps to reproduce

Run the following code

#include "opencv2/imgcodecs.hpp"
#include "opencv2/mcc.hpp"

int main(int, char**argv){
cv::Mat mat = cv::imread("./crop.jpeg");
cv::Ptr<cv::mcc::CCheckerDetector> detector = cv::mcc::CCheckerDetector::create();
detector->process(mat, cv::mcc::TYPECHART::MCC24);
}

with the image:

It might not SIGILL for you but you can display the mentioned cv::Point2f and you will see inf.

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc

[gursimarsingh]

@vrabaud I tried with 4.6 and 5.0, we are not able to reproduce this crash with the provided image

[vrabaud]

I could replicate it with 4.x at HEAD by displaying asp (which is a NaN)/v1 (which is -inf) in the code: you might not have a crash (if you do not have throwing NaNs), but you will have a NaN in the code.