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I am working with a LI-AR0820 GMSL2 camera which uses the On-Semi AR0820 sensor that captures images in a 12-Bit RCCC Bayer format. I want to read the real-time image stream from the camera and turn it into a grayscale image (using this demosaicing algorithm) and then feed it into an object detection algorithm. However, since OpenCV does not support the RCCC format I can't use the VideoCapture class to get image data from the camera. I am looking for something similar to get the streamed image data in an array-like format so that I can further manipulate it. Any ideas?

I'm running Ubuntu 18.04 with OpenCV 3.2.0 and Python 3.7.1.

EDIT. I am using the code here.

#include <vector>
#include <iostream>
#include <stdio.h>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>

int main() 
 // Each pixel is made up of 16 bits, with the high 4 bits always equal to 0
 unsigned char bytes[2];

 // Hold the data in a vector
 std::vector<unsigned short int> data;

 // Read the camera data
 FILE *fp = fopen("test.raw","rb");
 while(fread(bytes, 2, 1, fp) != 0) (bytes[1] << 8));
 

 // Make a matrix 1280x720 with 16 bits of unsigned integers
 cv::Mat imBayer = cv::Mat(720, 1280, CV_16U);

 // Make a matrix to hold RGB data
 cv::Mat imRGB;

 // Copy the data in the vector into a nice matrix
 memmove(imBayer.data, data.data(), data.size()*2);

 // Convert the GR Bayer pattern into RGB, putting it into the RGB matrix!
 cv::cvtColor(imBayer, imRGB, CV_BayerGR2RGB);

 cv::namedWindow("Display window", cv::WINDOW_AUTOSIZE);
 // *15 because the image is dark
 cv::imshow("Display window", 15*imRGB);

 cv::waitKey(0);

 return 0;

There are two problems with the code. First, I have to get a raw image file using fswebcam and then use the code above to read the raw file and display the image. I want to be able to access the /dev/video1 node and directly read the raw data from there instead of having to first save it and then read it separately. Second, OpenCV does not support the RCCC Bayer format so I have to come up with a demosaicing method.

The camera outputs serialized data through a Coax cable, so I use a Deser board with USB 3.0 connection to connect the camera to my laptop. The setup can be seen here.

If your camera supports the CAP_PROP_CONVERT_RGB property, you might be able to get raw RCCC data from VideoCapture. By setting this property to False, you can disable the conversion to RGB. So, you can capture raw frames using a code like (no error checking for simplicity):

cap = cv2.VideoCapture(0)
# disable converting images to RGB
cap.set(cv2.CAP_PROP_CONVERT_RGB, False)
while(True):
 ret, frame = cap.read()
 # other processing ...
cap.release()

I don't know if this works for your camera.

If you can get the raw images somehow, you can apply the de-mosaicing method described in the ANALOG DEVICES appnote.

with optimal filter

I wrote following python code as described in the appnote to test the RCCC -> GRAY conversion.

import cv2
import numpy as np

rgb = cv2.cvtColor(cv2.imread('RGB.png'), cv2.COLOR_BGR2RGB)
c = cv2.cvtColor(rgb, cv2.COLOR_RGB2GRAY)
r = rgb[:, :, 0]

# no error checking. c shape must be a multiple of 2
rmask = np.tile([[1, 0], [0, 0]], [c.shape[0]//2, c.shape[1]//2])
cmask = np.tile([[0, 1], [1, 1]], [c.shape[0]//2, c.shape[1]//2])

# create RCCC image by replacing 1 pixel out of 2x2 pixel region 
# in the monochrome image (c) with a red pixel
rccc = (rmask*r + cmask*c).astype(np.uint8)

# RCCC -> GRAY conversion
def rccc_demosaic(rccc, rmask, cmask, filt):
 # RCCC -> GRAY
 # use border type REFLECT_101 to give correct results for border pixels
 filtered = cv2.filter2D(src=rccc, ddepth=-1, kernel=filt, 
 anchor=(-1, -1), borderType=cv2.BORDER_REFLECT_101)

 demos = (rmask*filtered + cmask*rccc).astype(np.uint8)

 return demos

# demo of the optimal filter
zeta = 0.5
kernel_4neighbor = np.array([[0, 0, 0, 0, 0], 
 [0, 0, 1, 0, 0], 
 [0, 1, 0, 1, 0], 
 [0, 0, 1, 0, 0], 
 [0, 0, 0, 0, 0]])/4.0
kernel_optimal = np.array([[0, 0, -1, 0, 0], 
 [0, 0, 2, 0, 0], 
 [-1, 2, 4, 2, -1], 
 [0, 0, 2, 0, 0], 
 [0, 0, -1, 0, 0]])/8.0
kernel_param = np.array([[0, 0, -1./4, 0, 0], 
 [0, 0, 0, 0, 0], 
 [-1./4, 0, 1., 0, -1./4], 
 [0, 0, 0, 0, 0], 
 [0, 0, -1./4, 0, 0]])

# apply optimal filter (Figure 7)
opt1 = rccc_demosaic(rccc, rmask, cmask, kernel_optimal)
# parametric filter with zeta = 0.5 (Figure 5)
opt2 = rccc_demosaic(rccc, rmask, cmask, kernel_4neighbor + zeta * kernel_param)

# PSNR
print(10 * np.log10(255**2/((c - opt1)**2).mean()))
print(10 * np.log10(255**2/((c - opt2)**2).mean()))

Input RGB image:

Simulated RCCC image:

Gray image from de-mosaicing algorithm:

One more thing:

If your camera vendor provides an SDK for Linux, it may have an API to do the RCCC -> GRAY conversion, or at least get the raw image. If RCCC -> GRAY conversion is not in the SDK, the C# sample code should have it, so I suggest you take a look at their code.