Question

I’m new in JavaCV and want to create a Histogram from a image.

I tried to translate some C++ code into Java but JavaCV don’t have methods like cvCVtPixToPlane.

Can someone help me to create a histogram?

Answer 1

a translatet OpenCV-Code from the OpenCV-Wiki must be run.

I give you my code snipet to create a 1D-Diagram from the h-channel:

private CvHistogram getHueHistogram(IplImage image){
    if(image==null || image.nChannels()<3) new Exception("Error!");
    IplImage hsvImage= cvCreateImage(image.cvSize(), image.depth(), 3);
    cvCvtColor(image, hsvImage, CV_BGR2HSV);
    // Split the 3 channels into 3 images
    IplImageArray hsvChannels = splitChannels(hsvImage);
    //bins and value-range
    numberOfBins=255;
    float minRange= 0f;
    float maxRange= 180f;
    // Allocate histogram object
   int dims = 1;
   int[]sizes = new int[]{numberOfBins};
   int histType = CV_HIST_ARRAY;
   float[] minMax = new  float[]{minRange, maxRange};
   float[][] ranges = new float[][]{minMax};
    int uniform = 1;
    CvHistogram hist = cvCreateHist(dims, sizes, histType, ranges, uniform);
    // Compute histogram
    int accumulate = 1;
    IplImage mask = null;
    cvCalcHist(hsvChannels.position(0),hist, accumulate, null);
    return hist;
}

And my splitChannels-Method, i used in this snipet:

private IplImageArray splitChannels(IplImage hsvImage) {
    CvSize size = hsvImage.cvSize();
    int depth=hsvImage.depth();
    IplImage channel0 = cvCreateImage(size, depth, 1);
    IplImage channel1 = cvCreateImage(size, depth, 1);
    IplImage channel2 = cvCreateImage(size, depth, 1);
    cvSplit(hsvImage, channel0, channel1, channel2, null);
    return new IplImageArray(channel0, channel1, channel2);
}

If you want to draw a picture from the histogram you can iterate the bins. With cvQueryHistValue_1D() you can get the sum of pixels from bin_i