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You do this by setting up the config:

k4a_device_configuration_t config = K4A_DEVICE_CONFIG_INIT_DISABLE_ALL;
config.camera_fps = K4A_FRAMES_PER_SECOND_30;
config.color_format = K4A_IMAGE_FORMAT_COLOR_BGRA32; // <==== For Color image
config.color_resolution = K4A_COLOR_RESOLUTION_2160P;
config.depth_mode = K4A_DEPTH_MODE_NFOV_UNBINNED; // <==== For Depth image 
Then, once configured, you can capture a color image the following way, and then using the raw buffer create an opencv matrix from the color image:
k4a_image_t colorImage = k4a_capture_get_color_image(capture); // get image metadata
if (colorImage != NULL)
    // you can check the format with this function
    k4a_image_format_t format = k4a_image_get_format(colorImage); // K4A_IMAGE_FORMAT_COLOR_BGRA32 
    // get raw buffer
    uint8_t* buffer = k4a_image_get_buffer(colorImage);
    // convert the raw buffer to cv::Mat
    int rows = k4a_image_get_height_pixels(colorImage);
    int cols = k4a_image_get_width_pixels(colorImage);
    cv::Mat colorMat(rows , cols, CV_8UC4, (void*)buffer, cv::Mat::AUTO_STEP);
    // ...
    k4a_image_release(colorImage);
Similarly, for the depth image, you can convert the raw depth data to opencv like this (note, the matrix type has changed!):
k4a_image_t depthImage = k4a_capture_get_depth_image(capture); // get image metadata
if (depthImage != NULL)
    // you can check the format with this function
    k4a_image_format_t format = k4a_image_get_format(depthImage); // K4A_IMAGE_FORMAT_DEPTH16 
    // get raw buffer
    uint8_t* buffer = k4a_image_get_buffer(depthImage);
    // convert the raw buffer to cv::Mat
    int rows = k4a_image_get_height_pixels(depthImage);
    int cols = k4a_image_get_width_pixels(depthImage);
    cv::Mat depthMat(rows, cols, CV_16U, (void*)buffer, cv::Mat::AUTO_STEP);
    // ...
    k4a_image_release(depthImage);
  
NOTE: Opencv matrix constructor will not copy or allocate new memory
  for the pointer, instead it initializes the matrix head to point to
  the specified data!
                Fantastic answer, thank you. I was searching for something similar and while I was extremely close, I had my camera configured improperly, which was leading to errors. Thanks again!
– Archetype90
                Aug 1, 2019 at 16:34
                And maybe you can help further... I actually implemented exactly your code with an imwrite("C:\\test.jpg", colorMat) to write the image out. It worked great (which caused me to leave the above comment). I come back to it a few hours later and I am now getting an exception: (opencv_highgui2413d.dll) Acess Violation reading location. I am seeing this error all over the place from a Google search, but nothing too helpful or specific to my situation. Have you seen this before? Aware of what may be causing it?
– Archetype90
                Aug 1, 2019 at 20:39
                OK, going to leave the above comment in case anyone else has the issue. I was slightly wrong in what I said above - I had changed the code to attempt to write an image from a recording. But the recording was not in the proper format and that error was getting thrown. It is not a very explicit error, but as soon as I swapped over to the stream and had it configured as you stated above things worked great. Thanks again!
– Archetype90
                Aug 1, 2019 at 20:48
                Thanks for the answer. Can you explain how you initialize the capture variable? I tried to do this with k4a_capture_t capture; but this didn't work. If you have a full script, that would be great!
– user2835098
                Jan 31, 2020 at 17:55
    // Open the first plugged in Kinect device
    k4a_device_t device = NULL;
    if (K4A_FAILED(k4a_device_open(K4A_DEVICE_DEFAULT, &device)))
        printf("Failed to open k4a device!\n");
        return 1;
    // Get the size of the serial number
    size_t serial_size = 0;
    k4a_device_get_serialnum(device, NULL, &serial_size);
    // Allocate memory for the serial, then acquire it
    char *serial = (char*)(malloc(serial_size));
    k4a_device_get_serialnum(device, serial, &serial_size);
    printf("Opened device: %s\n", serial);
    free(serial);
    // Configure a stream of 4096x3072 BRGA color data at 15 frames per second
    k4a_device_configuration_t config = K4A_DEVICE_CONFIG_INIT_DISABLE_ALL;
    config.camera_fps       = K4A_FRAMES_PER_SECOND_30;
    config.color_format     = K4A_IMAGE_FORMAT_COLOR_BGRA32;
    config.color_resolution = K4A_COLOR_RESOLUTION_1080P;
    config.depth_mode = K4A_DEPTH_MODE_NFOV_UNBINNED;
    config.synchronized_images_only = true;
    // Start the camera with the given configuration
    k4a_device_start_cameras(device, &config);
    int frame_count = 0;
    k4a_device_get_capture(device, &capture, TIMEOUT_IN_MS);
    k4a_image_t color_image = k4a_capture_get_color_image(capture);
    uint8_t* color_buffer = k4a_image_get_buffer(color_image);
    int rows = k4a_image_get_height_pixels(color_image);
    int cols = k4a_image_get_width_pixels(color_image);
    cv::Mat color(rows, cols, CV_8UC4, (void*)color_buffer, cv::Mat::AUTO_STEP);
    //cv::imshow("random", color);
    k4a_image_t depth_image = k4a_capture_get_depth_image(capture);
    uint8_t* depth_buffer = k4a_image_get_buffer(depth_image);
    int depth_rows = k4a_image_get_height_pixels(depth_image);
    int depth_cols = k4a_image_get_width_pixels(depth_image);
    cv::Mat depth(depth_rows, depth_cols, CV_8UC4, (void*)depth_buffer, cv::Mat::AUTO_STEP);
    //cv::imshow("depth image",depth);
    //cv::waitKey(0);
    cv::imwrite("depth.jpg",depth);
    cv::imwrite("color.jpg",color);
    k4a_device_stop_cameras(device);
    k4a_device_close(device);
    return 0;
For complete build with cmake: https://github.com/ShitalAdhikari/Azure_kinect
        
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