Wavelet transform in openCV

Question

did someone tried to implement DWT in opencv or in C++? I saw older posts on this subject and i didn\'t find them useful for me, because I need a approximation coefficient a

Answer 1

I see that there's very few code examples for wavelet in java, especially if you're using openCV. I had to use wavelet in java with openCV and I used the C code from @la luvia and converted to java.

There was a lot of trouble while translating the code, because it had a lot of diferences in the openCV methods and ways of using it. This book helped me a lot in the process too.

I hope this code and the book give some perspective of how to use the lib and few diferences between the C and Java.

Here's the code:

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

public class Wavelet {

    //Imperative in java
    static{
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    }

    String pathname = "C:/Users/user/img096";


    public static void main(String[] args) {
        Wavelet wavelet = new Wavelet();
        wavelet.applyHaarFoward();
        wavelet.applyHaarReverse();

        Imgcodecs.imwrite(wavelet.pathname+"imi.jpg", wavelet.imi);
        Imgcodecs.imwrite(wavelet.pathname+"imd.jpg", wavelet.imd);
        Imgcodecs.imwrite(wavelet.pathname+"imr.jpg", wavelet.imr);
    }

    Mat im,im1,im2,im3,im4,im5,im6,temp,im11,im12,im13,im14,imi,imd,imr;
    float a,b,c,d;

    private void applyHaarFoward(){
        try{
            im = Imgcodecs.imread(pathname+".jpg", 0);
            imi = new Mat(im.rows(), im.cols(), CvType.CV_8U);
            im.copyTo(imi);

            //in CvType. If the number of channels is omitted, it evaluates to 1. 
            im.convertTo(im, CvType.CV_32F, 1.0, 0.0);
            im1 = new Mat(im.rows()/2, im.cols(), CvType.CV_32F);
            im2 = new Mat(im.rows()/2, im.cols(), CvType.CV_32F);

            im3 = new Mat(im.rows()/2, im.cols()/2, CvType.CV_32F);
            im4 = new Mat(im.rows()/2, im.cols()/2, CvType.CV_32F);

            im5 = new Mat(im.rows()/2, im.cols()/2, CvType.CV_32F);
            im6 = new Mat(im.rows()/2, im.cols()/2, CvType.CV_32F);


            // ------------------- Decomposition ------------------- 

            for (int rcnt = 0; rcnt < im.rows(); rcnt+=2) {
                for (int ccnt = 0; ccnt < im.cols(); ccnt++) {
                    //even though the CvType is float with only one channel
                    //the method Mat.get() return a double array 
                    //with only one position, [0].
                    a = (float) im.get(rcnt, ccnt)[0];
                    b = (float) im.get(rcnt+1, ccnt)[0];
                    c = (float) ((a+b)*0.707);
                    d = (float) ((a-b)*0.707);
                    int _rcnt= rcnt/2;
                    im1.put(_rcnt, ccnt, c);
                    im2.put(_rcnt, ccnt, d);

                }
            }

            for (int rcnt = 0; rcnt < im.rows()/2; rcnt++) {
                for (int ccnt = 0; ccnt < im.cols() - 2; ccnt+=2) {
                    a = (float) im1.get(rcnt, ccnt)[0];
                    b = (float) im1.get(rcnt, ccnt+1)[0];
                    c = (float) ((a+b)*0.707);
                    d = (float) ((a-b)*0.707);
                    int _ccnt = ccnt/2;
                    im3.put(rcnt, _ccnt, c);
                    im4.put(rcnt, _ccnt, d);
                }
            }

            for (int rcnt = 0; rcnt < im.rows()/2; rcnt++) {
                for (int ccnt = 0; ccnt < im.cols() - 2; ccnt+=2) {
                    a = (float) im2.get(rcnt, ccnt)[0];
                    b = (float) im2.get(rcnt, ccnt+1)[0];
                    c = (float) ((a+b)*0.707);
                    d = (float) ((a-b)*0.707);
                    int _ccnt = ccnt/2;
                    im5.put(rcnt, _ccnt, c);
                    im6.put(rcnt, _ccnt, d);
                }
            }

            imr = Mat.zeros(im.rows(), im.cols(), CvType.CV_32F);//imr = Mat.zeros(512, 512, CvType.CV_32F);
            imd = Mat.zeros(512, 512, CvType.CV_32F);
            im3.copyTo(imd.adjustROI(0, 0, 256, 256));
            im4.copyTo(imd.adjustROI(0, 255, 256, 256));
            im5.copyTo(imd.adjustROI(255, 0, 256, 256));
            im6.copyTo(imd.adjustROI(255, 255, 256, 256));





        }catch(Exception ex){
            System.err.println(ex.getLocalizedMessage());
            ex.printStackTrace();
        }
    }

    private void applyHaarReverse(){
        // ------------------- Reconstruction ------------------- 
                im11 = Mat.zeros(im.rows()/2, im.cols(), CvType.CV_32F);
                im12 = Mat.zeros(im.rows()/2, im.cols(), CvType.CV_32F);
                im13 = Mat.zeros(im.rows()/2, im.cols(), CvType.CV_32F);
                im14 = Mat.zeros(im.rows()/2, im.cols(), CvType.CV_32F);

                for (int rcnt = 0; rcnt < im.rows()/2; rcnt++) {
                    for (int ccnt = 0; ccnt < im.cols()/2; ccnt++) {
                        int _ccnt  = ccnt*2;
                        im11.put(rcnt, _ccnt, im3.get(rcnt, ccnt));
                        im12.put(rcnt, _ccnt, im4.get(rcnt, ccnt));
                        im13.put(rcnt, _ccnt, im5.get(rcnt, ccnt));
                        im14.put(rcnt, _ccnt, im6.get(rcnt, ccnt));
                    }
                }

                for (int rcnt = 0; rcnt < im.rows()/2; rcnt++) {
                    for (int ccnt = 0; ccnt < im.cols() - 2; ccnt+=2) {
                        a = (float) im11.get(rcnt, ccnt)[0];
                        b = (float) im12.get(rcnt, ccnt)[0];
                        c = (float) ((a+b)*0.707);
                        im11.put(rcnt, ccnt, c);
                        d = (float) ((a-b)*0.707);
                        im11.put(rcnt, ccnt+1, d);

                        a = (float) im13.get(rcnt, ccnt)[0];
                        b = (float) im14.get(rcnt, ccnt)[0];
                        c = (float) ((a+b)*0.707);
                        im13.put(rcnt, ccnt, c);
                        d = (float) ((a-b)*0.707);
                        im13.put(rcnt, ccnt+1, d);
                    }
                }

                temp = Mat.zeros(im.rows(), im.cols(), CvType.CV_32F);

                for (int rcnt = 0; rcnt < im.rows()/2; rcnt++) {
                    for (int ccnt = 0; ccnt < im.cols(); ccnt++) {
                        int _rcnt = rcnt*2;
                        imr.put(_rcnt, ccnt, im11.get(rcnt, ccnt));
                        temp.put(_rcnt, ccnt, im13.get(rcnt, ccnt));
                    }
                }


                for (int rcnt = 0; rcnt < im.rows()-2; rcnt+=2) {
                    for (int ccnt = 0; ccnt < im.cols(); ccnt++) {
                        a = (float) imr.get(rcnt, ccnt)[0];
                        b = (float) temp.get(rcnt, ccnt)[0];
                        c = (float) ((a+b)*0.707);
                        imr.put(rcnt, ccnt, c);
                        d = (float) ((a-b)*0.707);
                        imr.put(rcnt+1, ccnt, d);
                    }
                }

    }
}

Hope it's useful.