Problem setting color

hello,

i am facing a problem i can't solve.

i am creating a matrix of plain circles which i assign a color.

i defined a method in my Ball class which i use to set a color in ball setup :

ball::setup(float x, float y, float radius, ofColor c);

This method is written like follows :

void ball::setup(float x, float y, float r, ofColor col) {
    pin = ofPoint(x, y);
    position = pin;
    radius = r;
    velocity = ofPoint(0, 0);
    areaRadius = 25;
    dist = ofPoint(0,0);
    color.set(col);
}

i setup every ball like so :

this one works fine

balls.back().setup(x * ballRadius * 2, y * ballRadius * 2, ballRadius, ofColor(ofRandom(16), ofRandom(16), ofRandom(16)));

Capture d’écran 2015-08-31 à 16.56.08.png1848x1328 364 KB

but now i want to use an image to define each circle color :

in my ofApp::setup()

if(!image.loadImage("test.jpg")) cout << "error loading image" << endl;
image.resize(nbX, nbY);

then in setup each corcle color

balls.back().setup(x * ballRadius * 2, y * ballRadius * 2, ballRadius, image.getColor(x, y));

this doesn't work. I have only white circles.

Capture d’écran 2015-08-31 à 16.57.42.png1762x1360 136 KB