How to split OpenCV matrix while retaining continuity?

Question

I am trying to make a visual odometry algorithm work in real time (using my stereo camera). The camera feed gets returned as a single image (i420 pixel format), where I have to manually split the image into a left and right frame. One of the problems that I am running into is when I call cv::triangulatePoints. The function gives me an error saying that the input matrices (meaning the left and right frame) are not continuous.

When I receive the input image from the camera, using:

// Read camera feed
IMAGE_FORMAT fmt = {IMAGE_ENCODING_I420, 50};
BUFFER *buffer = arducam_capture(camera_instance, &fmt, 3000);
if (!buffer) 
    return -1;

// Store feed in image
cv::Mat image = cv::Mat(cv::Size(width,(int)(height * 1.5)), CV_8UC1, buffer->data);
arducam_release_buffer(buffer);

// Change image to grayscale (grayscale increases FPS)
cv::cvtColor(image, image, cv::COLOR_YUV2GRAY_I420);

if (!image.isContinuous())
    std::cout << "image is not continuous" << std::endl;

The image passes the continuity check fine (meaning the image is continuous).

However, after I resize and split the image into a left and right frame, using:

double scale_factor = 640.0 / width;
int custom_width = int(width * scale_factor);
int custom_height = int(height * scale_factor);

// OpenCV resize
cv::Mat frame = cv::Mat(cv::Size(custom_width, (int)(custom_height * 1.5)), CV_8UC1);
cv::resize(image, frame, frame.size(), 0, 0);
        
// Split image into left and right frame
cv::Mat frame_left = frame(cv::Rect(0, 0, custom_width / 2, (int)(custom_height * 1.5)));
cv::Mat frame_right = frame(cv::Rect(custom_width / 2, 0, custom_width / 2, (int)(custom_height * 1.5)));

if (!frame.isContinuous())
    std::cout << "frame is not continuous" << std::endl;
if (!frame_right.isContinuous())
    std::cout << "right frame is not continuous" << std::endl;
if (!frame_left.isContinuous())
    std::cout << "left frame is not continuous" << std::endl;

The resized image (frame) is continuous, but the left and right frames fail the continuity check (meaning they are not continuous).

So I guess my question is how can I split the image into two different images, while keeping them continuous?

user_6095478 · Answer

The solution to this problem is actually quite simple:

if (!frame_right.isContinuous()) {
                frame_right = frame_right.clone();
if (!frame_left.isContinuous()) {
                frame_left = frame_left.clone();

By using the clone() function, you can copy the image and OpenCV will consider it to be a new image. This way the right and left frames will retain continuity (or be set to continuous status).

So splitting the image destroys continuity and cloning will restore continuity.

How to split OpenCV matrix while retaining continuity?

1 Answers