Array to OpenCV matrix - c++

Question

I have a array double dc[][] and want to convert this as to a IplImage* image and further to a video frame.
What I had to do was I was given a video and I extracted out some features and then make a new video of the extracted features.
My approach was I divided the video into frames extracted the features from each frame then did the updation like this and in each iteration of frame I get a new dc
double dc[48][44];
for(int i=0;i<48;i++)
{
for(int j=0;j<44;j++)
{
dc[i][j]=max1[i][j]/(1+max2[i][j]);
}
}
Now I need to save this dc in such a way that I can reconstruct the video.Anybody help me with this.
Thanks in advance

Answer 1

If you're okay with using Mat, then you can make a Mat for existing user-allocated memory. One of the Mat constructors has the signature:
Mat::Mat(int rows, int cols, int type, void* data, size_t step=AUTO_STEP)
where the parameters are:
rows: the memory height,
cols: the width,
type: one of the OpenCV data types (e.g. CV_8UC3),
data: pointer to your data,
step: (optional) stride of your data
I'd encourage you to take a look at the documentation for Mat here
EDIT: Just to make things more concrete, here's an example of making a Mat from some user-allocated data
int main()
{
//allocate and initialize your user-allocated memory
const int nrows = 10;
const int ncols = 10;
double data[nrows][ncols];
int vals = 0;
for (int i = 0; i < nrows; i++)
{
for (int j = 0; j < ncols; j++)
{
data[i][j] = vals++;
}
}
//make the Mat from the data (with default stride)
cv::Mat cv_data(nrows, ncols, CV_64FC1, data);
//print the Mat to see for yourself
std::cout << cv_data << std::endl;
}
You can save a Mat to a video file via the OpenCV VideoWriter class. You just need to create a VideoWriter, open a video file, and write your frames (as Mat). You can see an example of using VideoWriter here
Here's a short example of using the VideoWriter class:
//fill-in a name for your video
const std::string filename = "...";
const double FPS = 30;
VideoWriter outputVideo;
//opens the output video file using an MPEG-1 codec, 30 frames per second, of size height x width and in color
outputVideo.open(filename, CV_FOURCC('P','I','M,'1'), FPS, Size(height, width));
Mat frame;
//do things with the frame
// ...
//writes the frame out to the video file
outputVideo.write(frame);
The tricky part of the VideoWriter is the opening of the file, as you have a lot of options. You can see the names for different codecs here