OpenMP Fractal Generator

I've been trying to create an openMP variant of the julia set, but I'm unable to create a coherent image when running more than one thread, I've been trying to solve what looks like a race condition but cannot find the error. The offending output looks like the required output along with "scanlines" across the entirety of the picture.

I've attached the code as well if its not clear enough.

#include <iostream>
#include <math.h>
#include <fstream>
#include <sstream>
#include <omp.h>
#include <QtWidgets>
#include <QElapsedTimer>
using namespace std;



double newReal(int x, int imageWidth){
    return 1.5*(x - imageWidth / 2)/(0.5 * imageWidth);
}

double newImaginary(int y, int imageHeight){
    return (y - imageHeight / 2) / (0.5 * imageHeight);
}

int julia(double& newReal, double& newImaginary, double& oldReal, double& oldImaginary, double cRe, double cIm,int maxIterations){
    int i;
    for(i = 0; i < maxIterations; i++){
      oldReal = newReal;
      oldImaginary = newImaginary;
      newReal = oldReal * oldReal - oldImaginary * oldImaginary + cRe;
      newImaginary = 2 * oldReal * oldImaginary + cIm;
      if((newReal * newReal + newImaginary * newImaginary) > 4) break;
    }
    return i;
}
int main(int argc, char *argv[])
{
    int fnum=atoi(argv[1]);
    int numThr=atoi(argv[2]);
//    int imageHeight=atoi(argv[3]);
//    int imageWidth=atoi(arg[4]);
//    int maxIterations=atoi(argv[5]);
//    double cRe=atof(argv[3]);
//    double cIm=atof(argv[4]);
    //double cRe, cIm;
    int imageWidth=10000, imageHeight=10000, maxIterations=3000;
    double newRe, newIm, oldRe, oldIm,cRe,cIm;
    cRe = -0.7;
    cIm = 0.27015;
    string fname;
    QElapsedTimer time;
    QImage img(imageHeight, imageWidth, QImage::Format_RGB888);//Qimagetesting
    img.fill(QColor(Qt::black).rgb());//Qimagetesting
    time.start();
    int i,x,y;
    int r, gr, b;
#pragma omp parallel for shared(imageHeight,imageWidth,newRe,newIm) private(x,y,i) num_threads(3)
        for(y = 0; y < imageHeight; y++)
        {
            for(x = 0; x < imageWidth; x++)
            {
                newRe = newReal(x,imageWidth);
                newIm = newImaginary(y,imageHeight);
                i= julia(newRe, newIm, oldRe, oldIm, cRe, cIm, maxIterations);

                r = (3*i % 256);
                gr = (2*(int)sqrt(i) % 256);
                b = (i % 256);
                img.setPixel(x, y, qRgb(r, gr, b));
             }
        }

    //stringstream s;
    //s << fnum;
    //fname= "julia" + s.str();
    //fname+=".png";
    //img.save(fname.c_str(),"PNG", 100);
    img.save("julia.png","PNG", 100);
    cout<< "Finished"<<endl;
    cout<<time.elapsed()/1000.00<<" seconds"<<endl;
}