sending Imagestream frame to Opencv fails - flutter

Question

The problem is while using the camera and passing frames by ImageStream,
I keep getting src->data == nullptr from the c++ code (OpenCV) while invoking the imdecode function. How come?
I have debugged the issue and I have found out in the getByte function,
I get:
img.height = 480
img.width = 720
In my opinion each plane should be of length 345600 (480*720)
but I got:
img.planes[0].bytes.length = 368592
img.planes[1].bytes.length = 184271
img.planes[2].bytes.length = 184271
How can it be the image's planes don't have the same length??
The following block is from the flutter app:
initCamera() {
cameraController = CameraController(cameras[0], ResolutionPreset.medium);
cameraController.initialize().then((value) {
if (!mounted) return;
setState(() {
cameraController.startImageStream((imageStream) {
cameraImage = imageStream;
print("Frame number: $frameCounter");
frameCounter++;
res = imageMetaData.applyConvertToMatrix(cameraImage);
// runModel();
});
});
});
}
Calling the c++ code by ffi:
Uint8List getBytes(CameraImage img) {
final WriteBuffer allBytes = WriteBuffer();
//Write all the values from a Uint8List into the buffer.
img.planes.forEach((plane) => allBytes.putUint8List(plane.bytes));
return allBytes.done().buffer.asUint8List();
}
Pointer<Uint8> intListToArray(Uint8List list) {
final Pointer<Uint8> ptr = calloc.allocate<Uint8>(list.length);
for (var i = 0; i < list.length; i++) {
ptr.elementAt(i).value = list[i];
}
return ptr;
}
Future<bool> applyConvertToMatrix(CameraImage img) async {
func_convert_to_matrix = nativeAddLib.lookup<NativeFunction<Pointer<Void> Function(
Pointer<Uint8>, Pointer<Int32>)>>("convert_from_img_array_to_matrix")
.asFunction();
Uint8List bytes = getBytes(img);
Pointer<void> ptr;
Pointer<Uint8> imgBytes;
imgByteLength.value = bytes.length;
imgBytes = intListToArray(bytes);
ptr = func_convert_to_matrix(imgBytes, imgByteLength); //invoking the c++ code
return true;
}
The C++ code:
void *convert_from_img_array_to_matrix(
unsigned char *img,
int32_t *imgLengthBytes) {
cv::Mat *src = new Mat();
int32_t len_bytes = *imgLengthBytes;
std::vector<unsigned char> m;
__android_log_print(ANDROID_LOG_VERBOSE, "NATIVE", "Len bytes: %d", len_bytes);
while ( len_bytes>=0 )
{
m.push_back(*(img++));
len_bytes--;
}
*src = cv::imdecode(m, cv::IMREAD_UNCHANGED);
if (src->data == nullptr)
{
__android_log_print(ANDROID_LOG_VERBOSE, "NATIVE", "You reached nullptr");
return nullptr;
}
if (DEBUG_NATIVE)
__android_log_print(ANDROID_LOG_VERBOSE, "NATIVE", "convert_from_img_array_to_matrix() --- len before:%d len after:%d width:%d height:%d",
*imgLengthBytes, src->step[0] * src->rows,
src->cols, src->rows);
*imgLengthBytes = src->step[0] * src->rows;
return src;
}
Can someone suggest what am I doing wrong?