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Your

IplImage copy = currentImage;

beacause at that point the image cannot be filled. Your callback is called in ros::spinOnce(), so before your first call of spinOnce() your currentImage is 100% empty.Afterwards it might be empty.

Check in your while loop and process only if filled:

ros::Rate loop_rate(5);

IplImage copy = currentImage; IplImage* frame = © // computation......ERROR while (ros::ok()) { ros::spinOnce();

   if ( !currentImage.empty() )

{ IplImage copy = currentImage;

 //other computations.......Error

}

    loop_rate.sleep();
}

Your

IplImage copy = currentImage;

beacause at that point the image cannot be filled. Your callback is called in ros::spinOnce(), so before your first call of spinOnce() your currentImage is 100% empty.Afterwards it might be empty.

Check in your while loop and process only if filled:

ros::Rate loop_rate(5);  
 
IplImage copy = currentImage;
IplImage* frame = ©
// computation......ERROR
while (ros::ok())
 {
        ros::spinOnce();ros::spinOnce();
  
    if ( !currentImage.empty() )
 
 {
 IplImage copy = currentImage;currentImage;
  
  //other computations.......Error
computations.
        }
  
}
 
     loop_rate.sleep();
 }