I'm using CV_MAT_ELEM to access the value of a cvmat without any problem, but when I use it in a for loop it gives me an error ( assertion failed ).
for (int i=0;i<=direction->cols;i++){
for(int j=0;j<=direction->rows;j++){
if ((CV_MAT_ELEM(*direction,float,i,j)<22.0) ) {
CV_MAT_ELEM(*direction,float,i,j)=0;
}
}
}
You are trying to access some pixels that are not within the image's range.
Try to change
for (int i=0;i<=direction->cols;i++){
^^
for(int j=0;j<=direction->rows;j++){
^^
to
for (int i=0;i<direction->cols;i++){
for(int j=0;j<direction->rows;j++){
P.S.: As #berak commented, you are still using old OpenCV API, i.e. using IplImage and CV_MAT_ELEM. Try to use the new API, i.e. Mat and at() correspondingly.
Related
I'm new to OpenCV and I stuck with the problem while declaring a Mat instance.
#include <opencv2\opencv.hpp>
int main(int argc, char *argv[]) {
cv::Mat before = cv::imread("./irene.jpg", CV_LOAD_IMAGE_COLOR);
cv::imshow("before", before);
cv::waitKey(0);
cv::Mat after(cv::Size(before.rows, before.cols), CV_8UC3);
for (int y = 0; y < before.rows; y++) {
for (int x = 0; x < before.cols; x++) {
after.at<cv::Vec3b>(y, x)[0] = before.at<cv::Vec3b>(y, x)[2];
after.at<cv::Vec3b>(y, x)[1] = before.at<cv::Vec3b>(y, x)[1];
after.at<cv::Vec3b>(y, x)[2] = before.at<cv::Vec3b>(y, x)[0];
}
}
cv::imshow("after", after);
cv::waitKey(0);
return 0;
}
Just a simple code for changing color of an image.
The problem is that, when I try to use cv::Size(), the compiler returns Assertion Failure. It builds okay, but when I try to press any key to go next of the code, it makes an exception.
What the compiler references and put on the console is:
OpenCV(3.4.3) Error: Assertion failed ((unsigned)(i1 *
DataType<_Tp>::channels) < (unsigned)(size.p[1] * channels())) in
cv::Mat::at, file
c:\opencv343\opencv\build\include\opencv2\core\mat.inl.hpp, line 1101
I'm certain on that the exception is thrown because of the Size() struct, because if I change Size(before.rows, before.cols) to before.rows, before.cols, it works fine!
I cannot figure out what is wrong, but all the tutorials say the code I tried is okay code.
This exception occurred because I set the width and height inside the Size() in wrong order.
Right order is cv::Size(width(cols)_of_image, height(rows)_of_image)
It was not a problem for many tutorials as they usually used image of square size.
I would like to display the elements in a vector in a listbox. However, I'm constantly getting a error: error C2664: 'System::Windows::Forms::ListBox::ObjectCollection::Add' : cannot convert parameter 1 from 'std::basic_string<_Elem,_Traits,_Alloc>' to 'System::Object ^'
I am using windows form in c++/cli.
this is the code:
for (size_t z = 0; z < container.size(); z++){
listBox_name->Items->Add(container[z]);
}
Based on the error message, your vector is a vector of std::string. Use marshal_as to convert the std::string to a managed String^ that the managed list box can accept.
for (size_t z = 0; z < container.size(); z++){
listBox_name->Items->Add(marshal_as<String^>(container[z]));
}
If you find you're doing this a lot, consider changing your vector of std::string to be a fully-managed type, such as List<String^>^.
I have recently started porting an application to a new platform which runs OpenCV 2.4.5.
Part of my code which uses OpenCV's implementation of FLANN to do hierarchical clustering no longer compiles.
The code is as follows:
cv::Mat mergedFeatures = cvCreateMat(descriptorTotal, descriptorDims, CV_32F);
int counter = 0;
for (uint j = 0; j < ImageFeatures.size(); j++) {
cv::Mat features = ImageFeatures[j];
for (int k = 0; k < features.rows; k++) {
cv::Mat roi = mergedFeatures.row(counter);
features.row(k).copyTo(roi);
counter++;
}
}
cv::Mat centers = cvCreateMat(1000, descriptorDims, CV_32FC1);
cv::flann::KMeansIndexParams k_params = cv::flann::KMeansIndexParams();
cv::flann::AutotunedIndexParams atp = cv::flann::AutotunedIndexParams();
int numClusters = cv::flann::hierarchicalClustering<float, float>(mergedFeatures, centers, k_params);
The error that I am getting (in Eclipse) is that cv::flann::hierarchicalClustering has invalid arguments and that neither of the candidates for this function are met.
Can someone explain how I suddenly seem to be calling this method incorrectly?
Many thanks for any help.
I fixed the problem myself.
Instead of accepting:
cv::flann::KMeansIndexParams k_params
the hierarchicalClustering function actually needs:
cvflann::KMeansIndexParams k_params
It is rather a confusing namespace convention with the FLANN library in OpenCV and I had just overlooked the namespace difference in what the compiler error was telling me.
It is all working now. The KMeansIndexParams type is present in both namespaces and I guess that the hierarchicalClustering method has changed very slightly from OpenCV 2.3 to 2.4.5.
As a result of a call to estimateRigidTransform() I get a cv::Mat object named "trans". To retrieve its contained matrix I try to access its elements this way:
for (i=0; i<2; i++) for (j=0; j<3; j++)
{
mtx[j][i]=CV_MAT_ELEM(trans,double,i,j);
}
Unfortunately with VS2010 I get a compiler error
error C2228: left of '.ptr' must have class/struct/union
for the line with CV_MAT_ELEM. When I unwrap this macro I find something like
(mat).data.ptr + (size_t)(mat).step*(row) + (pix_size)*(col))
When I remove the ".ptr" behind (mat).data it compiles. But I can't imagine that's the solution (or can't imagine that's a bug and I'm the only one who noticed it). So what could be wrong here really?
Thanks!
You don't access the mat elements like this. For a traversal see my other answer here with sample code:
color matrix traversal
or see the opencv refman for grayscale Mat:
Mat M; // should be grayscale
int cols = M.cols, rows = M.rows;
for(int i = 0; i < rows; i++)
{
const double* Mi = M.ptr<double>(i);
for(int j = 0; j < cols; j++)
{
Mi[j]; // is the matrix element.
}
}
Just an addendum from my side: meanwhile I found CV_MAT_ELEM expects a structure CvMat (OpenCV-C-interface) but not cv::Mat (the C++-interface). That's why I get this funny error. Conversion from cv::Mat to CvMat can be done simply by casting to CvMat. Funny confusion with the C and C++ interfaces in OpenCV...
I'm using cv::imread to load a image and do some processes with that image,
but I don't know why I can't read values of the returned Mat from imread function.
I used Mat.at method:
Mat iplimage = imread("Photo.jpg",1); //input
for(int i=0;i<iplimage.rows;i++){
for(int j=0;j<iplimage.cols;j++){
cout<<(int)iplimage.at<int>(i,j)<<" ";
}
cout<<endl;
}
But it appeared an error:
OpenCV Error: Assertion failed ( dims <= 2 && data && (unsigned)i0 <
(unsigned)size.p[0] &&
(unsigned)(i1*DataType<_Tp>::channels) < (unsigned)(size.p[1]*channels()) &&
((((Sizeof(size_t)<<28)|0x8442211) >> ((DataType<_Tp>::depth) & ((1 << 3) -1))*4) & 15)
== elemSize1()) is unknown function, file: "c:\opencv2.2\include\opencv2\core\mat.hpp", line 517
But it is ok if I use the direct access way:
Mat iplimage = imread("Photo.jpg",1); //input
for(int i=0;i<iplimage.rows;i++){
for(int j=0;j<iplimage.cols;j++){
cout<<(int)iplimage.data[i*iplimage.cols + j]<<" ";
}
cout<<endl;
}
Could anyone tell me how can I use the Mat.at method to access the above Mat?
Thanks for your help!
See this answer. In your case, the returned Mat is 3 dimensional, hence iplimage.at<int> fails the assertion, you just need to access the intensities in each channel like the way the mentioned answer explain.
you are trying to load with 3 channel of image it will be fine if you change to this Mat iplimage = imread("Photo.jpg",0); //input
I found the solution. It is because I used :
inputImage.at<int>(i,j) or inputImage.at<float>(1,2)
instead of, (int)inputImage.at<uchar>(1,2) or (float)inputImage.at<uchar>(1,2)
Sorry for my carelessness!
Mat iplimage = imread("Photo.jpg",1) this read in a 3 channel colour image. You can use Mat iplimage = imread("Photo.jpg",0) to read in the image as greyscale so that your iplimage.at(i,j) would work. Please note that you should use .at if your image is 8bit instead of .at.
If your image is not 8bit, you should use iplimage = imread("Photo.jpg",CV_LOAD_IMAGE_ANYDEPTH)