access pixel and check if is inf pixel

Question

I searched on the web and didn't find any good answer for my problem. So this is my question: I am using OpenCV and have a function called replaceInvalidDisparties and I have to search through the pixels and check if the actual value is inf and there is a standard function in OpenCv called cvIsInf(double value) to check if the value is inf, but somehow i always get segmentation fault.

using namespace cv;
cv::Mat replaceInvalidDisparities(const cv::Mat &original_disp)
{
  cv::Mat output = orignal_disp.clone();

  //access pixel

  for(int i = 0; i< output.rows; i++)
  {
    for(int j=0; j<output.cols; j++)
   {
      //now here i want to check if the actual pixel is inf
      cvIsInf(output.at<double>(i,j));
   }
  }
}

But somehow it always give me a segmentation fault. Does anyone know the problem?

score 0 · Answer 1 · answered Mar 14 '18 at 10:42

0

The first problem, i see is that you don't use return value of the cvIsInf function. According to opencv docs: https://docs.opencv.org/3.1.0/db/de0/group__core__utils.html#gae04046b1211c77ff19a535bd78c15964, The function returns 1 if the argument is a plus or minus infinity (as defined by IEEE754 standard) and 0 otherwise.

So, you should replace your code inside loop to smth like this:

if (cvIsInf(output.at<double>(i,j))) {
  output.at<double>(i,j) = new_value;
}

The second problem is that you doesn't return output matrix from the function:

return output;

answered Mar 14 '18 at 10:42

Aleksey Petrov

370
2
15

Thanks for the answer! Yeah i tried this but somehow there is always a segmentationfault if i run my program dont know why... – Newuser1234567 Mar 14 '18 at 10:52
Are you sure that segmentation fault caused by this function? – Aleksey Petrov Mar 14 '18 at 11:00
yeah, normally when i erase this two for loops and the cvisInf functijon there are no problems – Newuser1234567 Mar 14 '18 at 11:10
Are you sure that your original_disp Mat contains doubles and not other type? – Aleksey Petrov Mar 14 '18 at 11:19
i found my problem it was the opencV 3.1 cause the program only runs on 2.4.9 – Newuser1234567 Mar 16 '18 at 17:14

score 0 · Answer 2 · answered Mar 15 '18 at 15:28

First of all, make sure you do return a value. Not returning a value is an undefined behavior: Is a return statement mandatory for C++ functions that do not return void?.

Rest of the function doesn't seems to be the cause of the segmentation fault, I would suggest changing

cv::Mat output = orignal_disp.clone();

to

cv::Mat output(100, 100, CV_64F);

Just to make sure your matrix is not ill-formed. (Was going to comment; didn't have enough reputation.)

thx! i found the problem it was the opencV version but thanks for the tip! — Newuser1234567, Mar 16 '18 at 17:14

access pixel and check if is inf pixel

2 Answers2