OpenCV Android template matching from camera

Question

I'm trying to match an image with the camera input in Android. When I try this with 2 images everything works just fine. But now I like to do the same thing with the camera input. To get this done I implemented CvCameraViewListener2 and tried the following code:

@Override
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
    mRgba = inputFrame.rgba();
    int match_method = Imgproc.TM_CCOEFF;

    mSizeRgba = mRgba.size();

    int rows = (int) mSizeRgba.height;
    int cols = (int) mSizeRgba.width;

    Mat templ = Highgui.imread(getFileAbsPath("template.jpg"));

    // Create the result matrix
    int result_cols = cols - templ.cols() + 1;
    int result_rows = rows - templ.rows() + 1;

    Mat result = new Mat(result_rows, result_cols, CvType.CV_32F);

    Mat src = new Mat(result_rows, result_cols, CvType.CV_32F);
    mRgba.convertTo(src, CvType.CV_32F);

    Mat template = new Mat(templ.rows(), templ.cols(), CvType.CV_32F);
    templ.convertTo(template, CvType.CV_32F);

    // Do the Matching and Normalize
    Imgproc.matchTemplate(src, templ, result, match_method);
    Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());

    // Localizing the best match with minMaxLoc
    MinMaxLocResult mmr = Core.minMaxLoc(result);

    Point matchLoc;
    if (match_method == Imgproc.TM_SQDIFF
            || match_method == Imgproc.TM_SQDIFF_NORMED) {
        matchLoc = mmr.minLoc;
    } else {
        matchLoc = mmr.maxLoc;
    }
    Rect roi = new Rect((int) matchLoc.x, (int) matchLoc.y, templ.cols(),
            templ.rows());
    // Mat cropped = new Mat(mRgba, roi);
    Core.rectangle(result, new Point(roi.x, roi.y), new Point(roi.width - 2, roi.height - 2), new Scalar(255, 0, 0, 255), 2);
    return mRgba;
}

When I run this code I get this OpenCV error:

OpenCV Error: Assertion failed ((img.depth() == CV_8U || img.depth() == CV_32F) 
                                          && img.type() == templ.type()) in ...

Can anyone help me with this problem?

Thanks

score 3 · Answer 1 · answered Aug 21 '13 at 10:02

I solved my problem. I needed to convert the color of the template from BGR to RGBA. With the following code i have no crashes anymore but the camera frames in the preview are very slow. This is not exactly what I want.

    public void initialize(){
    if (src.empty())
        return;
    if(template == null){
        Mat templ = Highgui.imread(getFileAbsPath("template.png"), Highgui.CV_LOAD_IMAGE_UNCHANGED);
        template = new Mat(templ.size(), CvType.CV_32F);
        Imgproc.cvtColor(templ, template, Imgproc.COLOR_BGR2RGBA);
    }
}

@Override
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {

    src = inputFrame.rgba();
    initialize();
    int match_method = Imgproc.TM_SQDIFF;

    // Create the result matrix
    int result_cols = src.cols() - template.cols() + 1;
    int result_rows = src.rows() - template.rows() + 1;
    Mat result = new Mat(result_rows, result_cols, CvType.CV_32F);

    // Do the Matching and Normalize
    Imgproc.matchTemplate(src, template, result, match_method);
    Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());

    // Localizing the best match with minMaxLoc
    MinMaxLocResult mmr = Core.minMaxLoc(result);

    Point matchLoc;
    if (match_method == Imgproc.TM_SQDIFF || match_method == Imgproc.TM_SQDIFF_NORMED) {
        matchLoc = mmr.minLoc;
    } else {
        matchLoc = mmr.maxLoc;
    }

    Rect roi = new Rect((int) matchLoc.x, (int) matchLoc.y, template.cols(), template.rows());
    Core.rectangle(src, new Point(roi.x, roi.y), new Point(roi.width - 2, roi.height - 2), new Scalar(255, 0, 0, 255), 2);
    return src;
}

what is the alternative way to make it more better? – Mehul Joisar Mar 13 '15 at 06:28 — Mehul Joisar, Mar 13 '15 at 06:28
@Sam Ram can you give me the complete code? Thank's – wiki Sep 28 '18 at 14:24 — wiki, Sep 28 '18 at 14:24

score 1 · Answer 2 · answered Aug 20 '13 at 14:27

1

The error suggests the template and the src are not compatible in terms of channels and size.

// Do the Matching and Normalize
    Imgproc.matchTemplate(src, templ, result, match_method);

Are you sure it should be temp1? It seems you performed a lot of conversion to template

answered Aug 20 '13 at 14:27

SolessChong

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Indeed it was an attempt to get the Mat objects compatible but probably the wrong way... Imgproc.matchTemplate(src, template, result, match_method); gives the same error. – Smek Aug 20 '13 at 14:34
I mean, I suggest `Imgproc.matchTemplate(src, template, result, match_method);` – SolessChong Aug 20 '13 at 14:41
Yes i tried just that but it does not work. I tested the types of the Mat objects src and template they don't match. How can i convert them to the same type? – Smek Aug 20 '13 at 14:47
@Smek: please post the alternative way if you have implemented. I am facing same issue like yours. – Mehul Joisar Mar 13 '15 at 06:29

OpenCV Android template matching from camera

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