Image dispersion

Hi I am coming from Processing, and looking to use an image’s colours to draw rectangles that disperse by mapping the brightness value of the pixels to mouseX. then feeding that number into the z value: this is what I have so far:

#include "ofApp.h"

void ofApp::setup(){
    cellSize = 2;
    cols = img.getWidth()/cellSize;
    rows = img.getHeight()/cellSize;
void ofApp::update(){

void ofApp::draw(){
//    img.draw(0,0);
    for (int i = 0; i > cols; i++){
        for (int j = 0; j < rows; j++){
            int x = i*cellSize + cellSize/2;
            int y = j*cellSize + cellSize/2;
            int loc = x + y*ofGetWidth();
            ofColor c = img.getColor(x,y);
            int b = c.getBrightness();
            cout << b << endl;
            float z = ofMap(b,0,255,0,mouseX);
            ofTranslate(x, y, z);
            ofDrawRectangle(0, 0, cellSize, cellSize);

So far I just keep getting a blank screen.
Any help appreciated

Maybe this typo?
for (int i = 0; i < cols; i++){
< instead of >

wow, great catch, thank you.