OpenCV image array, 4D matrix

Question

I am trying to store a IPL_DEPTH_8U, 3 channel image into an array so that I can store 100 images in memory.

To initialise my 4D array I used the following code (rows,cols,channel,stored):

int size[] = { 324, 576, 3, 100 };
CvMatND* cvImageBucket; = cvCreateMatND(3, size, CV_8U);

I then created a matrix and converted the image into the matrix

CvMat *matImage = cvCreateMat(Image->height,Image->width,CV_8UC3 );
cvConvert(Image, matImage );

How would I / access the CvMatND to copy the CvMat into it at the position of stored?

e.g. cvImageBucket(:,:,:,0) = matImage; // copied first image into array

check this out stackoverflow.com/questions/6493687/…

Boaz
– Boaz

2011-12-05 14:54:27 +00:00
Commented Dec 5, 2011 at 14:54 — Boaz
– Boaz, Commented Dec 5, 2011 at 14:54

Chris · Accepted Answer · 2011-12-05 15:39:03Z

2

You've tagged this as both C and C++. If you want to work in C++, you could use the (in my opinion) simpler cv::Mat structure to store each of the images, and then use these to populate a vector with all the images.

For example:

std::vector<cv::Mat> imageVector;
cv::Mat newImage;

newImage = getImage();       // where getImage() returns the next image,
                             // or an empty cv::Mat() if there are no more images
while (!newImage.empty())
{
    // Add image to vector
    imageVector.push_back(image);

    // get next image
    newImage = getImage();
}

answered Dec 5, 2011 at 15:39

Chris

8,2184 gold badges40 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Smash · Accepted Answer · 2011-12-05 14:52:53Z

0

I'm guessing something similar to:

for ith matImage

memcpy((char*)cvImageBucket->data+i*size[0]*size[1]*size[2],(char*)matImage->data,size[0]*size[1]*size[2]);

answered Dec 5, 2011 at 14:52

Smash

3,8124 gold badges36 silver badges54 bronze badges

Comments

smttsp · Accepted Answer · 2020-03-22 04:16:34Z

Although I agree with @Chris that it is best to use vector<Mat> rather than a 4D matrix, this answer is just to be a reference for those who really need to use 4D matrices in OpenCV (even though it is a very unsupported, undocumented and unexplored thing with so little available online and claimed to be working just fine!).

So, suppose you filled a vector<Mat> vec with 2D or 3D data which can be CV_8U, CV_32F etc.

One way to create a 4D matrix is

vector<int> dims = {(int)vec.size(), vec[0].rows, vec[0].cols};
Mat m(dims, vec[0].type(), &vec[0]);

However, this method fails when the vector is not continuous which is typically the case for big matrices. If you do this for a discontinuous matrix, you will get a segmentation fault or bad access error when you would like to use the matrix (i.e. copying, cloning, etc). To overcome this issue, you can copy matrices of the vector one by one into the 4D matrix as follows:

Mat m2(dims, vec[0].type());
for (auto i = 0; i < vec.size(); i++){
    vec[i].copyTo(temp.at<Mat>(i));
}

Notice that both methods require the matrices to be the same resolution. Otherwise, you may get undesired results or errors.

Also, notice that you can always use for loops but it is generally not a good idea to use them when you can vectorize.

Collectives™ on Stack Overflow

OpenCV image array, 4D matrix

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related