Converting inputFrame from Camera to HSI using OpenCV in Android

Question

I want to convert an image from Android camera to HSI format using OpenCV. The problem is when I use the following method

private Mat rgb2hsi(Mat rgbFrame) {
    Mat hsiFrame = rgbFrame.clone();

    for( int i = 0; i < rgbFrame.rows(); ++i ) {
        for( int j = 0; j < rgbFrame.cols(); ++j ) {
            double[] rgb = rgbFrame.get(i, j);
            Log.d(MAINTAG, "rgbFrame.get(i, j) array size = " + rgb.length);
            double colorR = rgb[0];
            double colorG = rgb[1];
            double colorB = rgb[2];

            double minRGB = min(colorR, colorG, colorB);
            double colorI = (colorR + colorG + colorB) / 3;
            double colorS = 0.0;

            if(colorI > 0) colorS = 1.0 - (minRGB / colorI);

            double colorH;
            double const1 = colorR - (colorG / 2) - (colorB / 2);
            double const2 = Math.sqrt(Math.pow(colorR, 2) + Math.pow(colorG, 2) + Math.pow(colorR, 2)
                            - (colorR * colorG) - (colorR * colorB) - (colorG * colorB));

            colorH = Math.acos(const1 / const2);
            if(colorB > colorG) colorH = 360 - colorH;

            double[] hsi = {colorH, colorS, colorI};
            hsiFrame.put(i, j, hsi);
        }
    }


    return hsiFrame;
}

It shows an error

java.lang.UnsupportedOperationException: Provided data element number (3) should be multiple of the Mat channels count (4)

I search for a while to figure out the cause of this error.
I found that I put an array of size 3 instead of 4.
Android convert byte array from Camera API to color Mat object openCV
I wonder what Type of image receive from Android Camera.
Why when I get an array of size 4?
How to convert an image received from Android camera to HSI and preview on the screen?

The following is the overrided method onCameraFrame

public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
    Mat outputFrame = inputFrame.rgba();

    /* Get RGB color from the pixel at [index_row, index_column] */
    int index_row = 0;
    int index_column = 0;
    final double[] mRgb_pixel = outputFrame.get(index_row, index_column);

    /* Show the result */
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            int r = (int) mRgb_pixel[0];
            int g = (int) mRgb_pixel[1];
            int b = (int) mRgb_pixel[2];
        /* Set RGB color */
            mRred_textview.setText("Red\n" + Double.toString(mRgb_pixel[0]));
            mGreen_textview.setText("Green\n" + Double.toString(mRgb_pixel[1]));
            mBlue_textview.setText("Blue\n" + Double.toString(mRgb_pixel[2]));
            mColor_textview.setBackgroundColor(Color.rgb(r, g, b));
        }
    });

    if(mPreviewType == PreviewType.GB) {
        outputFrame.convertTo(outputFrame, CvType.CV_64FC3);
        return getGBColor(rgb2hsi(outputFrame));
    } else if (mPreviewType == PreviewType.HSI) {
        outputFrame.convertTo(outputFrame, CvType.CV_64FC3);
        return rgb2hsi(outputFrame);
    } else {
        return outputFrame;
    }
}

My MainActivity implements CameraBridgeViewBase.CvCameraViewListener2

[Edit]
I think that the reason why it return an array of size 4 is because the frame is in RGBA format, not RGB format.
Therefore, how to convert RGBA to HSI and preview the frame on the screen?

nisargthakkar · Accepted Answer · 2015-06-18 19:18:16Z

1

The problem here is that your hsiFrame is a 4 channel image and your hsi array has only 3 values. You need to add one term corresponding to alpha channel to your hsi array. Making either of the following changes should work for you:

1. double[] hsi = {colorH, colorS, colorI, rgb[3]};
2. Mat hsiFrame = new Mat(rgbFrame.size(), CvType.CV_8UC3);

Hope this helps.

answered Jun 18, 2015 at 19:18

nisargthakkar

431 silver badge5 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Converting inputFrame from Camera to HSI using OpenCV in Android

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related