Cannot convert OpenCV Mat to IMAQ image.ctl format

[zhangj14]

Hi all,

I'm using LabVIEW 2016 with the NIVision OpenCV Utility installed. I'm trying to learn calling OpenCV library from LabVIEW so I build a very simple VI that grabs image from webcam, do a thresholding (OpenCV library), and output the result image. The OpenCV part works fine as I can save the images from OpenCV code. However I encountered this problem that the image cannot be displayed or saved in LabVIEW panel. 

I've checked the sample "OpenCV motion detection" as it also has an image output. I noted there are basically three lines of codes I need to add in for the conversion, which I have followed exactly in my codes:

EXTERN_C void NI_EXPORT NIVisOpenCV_GetMovingObjectMask(int handle, NIImageHandle sourceHandle, NIImageHandle outMaskHandle, NIErrorHandle errorHandle){

NIImage mask(outMaskHandle);

...
Mat outMask;

...
ThrowNIError(mask.MatToImage(outMask));

}

I attach my VI and codes here. Hope can have some suggestions. Thanks!

EXTERN_C void NI_EXPORT NIVisOpenCV_Test(int thre, NIImageHandle sourceHandle, NIImageHandle grayImageHandle, NIArrayHandle rectLV, NIErrorHandle errorHandle)
{
NIERROR error = NI_ERR_SUCCESS;
ReturnOnPreviousError(errorHandle);
try {
NIImage source(sourceHandle);
NIImage gray(grayImageHandle);

NIArray1D<LV_Rect> rect(rectLV);

//Do image conversions
Mat sourceMat;
ThrowNIError(source.ImageToMat(sourceMat));

Mat greyImg, procImg;
cvtColor(sourceMat, greyImg, CV_BGR2GRAY);
threshold(greyImg, procImg, thre, 255, THRESH_BINARY_INV);

imwrite("D:\\proc.jpg", procImg);
ThrowNIError(gray.MatToImage(greyImg));

}
catch (NIERROR _err) {
error = _err;
}
catch (...) {
error = NI_ERR_OCV_USER;
}
}