[OpenCV] Issue with SetTo Method in Mat Class.

[Omar122]

Hello,

I am not sure if this is a technical issue or a functional one.

I have an issue with SetTo method. output is always greyscaled not sure why.
Should I try to convert it? if so what value should I use?
Because I keep getting error related to the number of channels in the input.

Exception in thread "main" java.lang.RuntimeException: OpenCV(4.6.0) D:\a\javacpp-presets\javacpp-presets\opencv\cppbuild\windows-x86_64-gpu\opencv-4.6.0\modules\imgproc\src\color.simd_helpers.hpp:92: error: (-2:Unspecified error) in function '__cdecl cv::impl::`anonymous-namespace'::CvtHelper<struct cv::impl::`anonymous namespace'::Set<1,-1,-1>,struct cv::impl::A0xc698e769::Set<3,4,-1>,struct cv::impl::A0xc698e769::Set<0,2,5>,2>::CvtHelper(const class cv::_InputArray &,const class cv::_OutputArray &,int)'
> Invalid number of channels in input image:
>     'VScn::contains(scn)'
> where
>     'scn' is 4

This is my Code:

 adaptiveThreshold(gray, threash, 50, ADAPTIVE_THRESH_MEAN_C, THRESH_BINARY, 5, 3.3);
        Mat label = new Mat(threash.size(), CV_32S);
        imwrite("gray.jpg", gray);
        imwrite("thresh.jpg", threash);
        //int connectedComponents = opencv_imgproc.connectedComponents(gray, label);
        int connectedComponents = opencv_imgproc.connectedComponents(threash, label, 8, CV_32S);
      

        if (connectedComponents < 2) {
        } else {
            Mat output = Mat.zeros(gray.size(), CV_64FC4).asMat();
            RNG rng = new RNG(0xFFFFFFFF);
            for (int i = 1; i <= connectedComponents; i++) {
                Scalar color = new Scalar(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255), 255);
                Mat mask = opencv_core.equals(label, i).asMat();
                output = output.setTo(new Mat(color), mask);

            }
            //Mat finaloutput = new Mat();
            //cvtColor(output, finaloutput, opencv_imgproc.COLOR_GRAY2RGBA);
            imwrite("output.jpg", output);
            //imwrite("finaloutput.jpg", finaloutput);

Git repo: https://github.com/Omar122/OpencvLearn.git

[saudet]

On which line are you getting this error?

If you're having issues with Mat.setTo(), did you try to call it more simply like this?

output = output.setTo(new Mat(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255), 255), mask);

[Omar122]

That worked. I thought I could just pass a Scalar object.

[saudet]

No, the C++ API wants an cv::InputArray, which can be created from a cv::Scalar, cv::Mat, std::vector, etc, but for simplicity JavaCPP just maps everything to cv::Mat because it's simpler like that.