How do I return calculated Histogram results from OpenCV back to LabVIEW? I have no problems creating my DLL and sending images back & forth between LabVIEW and OpenCV DLL's.

[jodi319]

Here is the code I am working with:

#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2\highgui\highgui.hpp>

using namespace std;
using namespace cv;

// extern C
extern "C" {

	_declspec (dllexport) int MyHistCalc(unsigned char *imageIN, int rows, int cols, double threshold1, double threshold2, int kernel_size, unsigned char *imageOUT, unsigned char *HistCalcImageOUT);
}



_declspec (dllexport) int MyHistCalc(unsigned char *imageIN,
	int rows,
	int cols,
	double threshold1,
	double threshold2,
	int kernel_size,
	unsigned char *imageOUT,
	unsigned char *HistCalcImageOUT)
{
	Mat image_input(rows, cols, CV_8U, &imageIN[0]); // THIS IS THE INPUT IMAGE, POINTER TO DATA
	Mat image_output(rows, cols, CV_8U, &imageOUT[0]); // THIS IS THE INPUT IMAGE, POINTER TO DATA
	Mat image_histcalcoutput(512, 400, CV_8U, &HistCalcImageOUT[0]);

	//Mat gray = imread("image.jpg", 0);
	namedWindow("Gray", 1);    imshow("Gray", image_input);
	image_output = image_input;
	namedWindow("Image Output", 1);    imshow("Image Output", image_output);
	// Initialize parameters
	int histSize = 256;    // bin size
	float range[] = { 0, 255 };
	const float *ranges[] = { range };

	// Calculate histogram
	MatND hist;
	//hist is a 256x1 array

	calcHist(&image_input, 1, 0, Mat(), hist, 1, &histSize, ranges, true, false);

	// Plot the histogram
	int hist_w = 512; int hist_h = 400;
	int bin_w = cvRound((double)hist_w / histSize);

	Mat histImage(hist_h, hist_w, CV_8UC1, Scalar(0, 0, 0));
	normalize(hist, hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
	//image_histcalcoutput = hist;

	for (int i = 1; i < histSize; i++)
	{
		line(histImage, Point(bin_w*(i - 1), hist_h - cvRound(hist.at<float>(i - 1))),
			Point(bin_w*(i), hist_h - cvRound(hist.at<float>(i))),
			Scalar(255, 0, 0), 2, 8, 0);
	}

	image_histcalcoutput = histImage;
	namedWindow("CalcHist Result 1", 1);    imshow("CalcHist Result 1", histImage);
	namedWindow("CalcHist Result 2", 1);    imshow("CalcHist Result 2", image_histcalcoutput);

	waitKey(0);
	return histSize;
}

I am unsure if my problem is catching image_histcalcoutput incorrectly in LabVIEW or returning result correctly.

Please find screenshot of my VI attached.

[Hatef.fouladi]

why you do not use labview vision histogram? it is so easy to use

[jodi319]

My question (and implementation) is part of a bigger problem with portions already utilising OpenCV.

[Hatef.fouladi]

ok if you have to use open cv in lab vie any way
I could give you some link and video I hope they could solve your problem
https://www.youtube.com/watch?v=M6v9Xf4_KaI

https://lavag.org/topic/2179-open-source-alternative-to-imaq-vision-toolkit/

https://www.ehe-lab.com/OpenCV%20Wrapper%20for%20LabVIEW%20installation%20guide.pdf

https://sourceforge.net/projects/emgucv/

http://forums.ni.com/t5/LabVIEW/labview-opencv/m-p/1650770/highlight/true#M591760

http://forums.ni.com/t5/Machine-Vision/Want-to-use-OpenCV-function-in-LabVIEW/m-p/3053705/highlight/...