ofImage to ofBuffer not working... why?

testApp.cpp

#include "testApp.h"

//--------------------------------------------------------------
void testApp::setup(){
    
    ofImage foo;
    foo.loadImage("walrus.jpg");
    
    ofPixels px;
    px.setFromPixels(foo.getPixels(), foo.width, foo.height, foo.getPixelsRef().getImageType());
    
    ofBuffer imageBuffer;
    ofSaveImage(px, imageBuffer);
    
    cout << imageBuffer << endl; 

}

testApp.h

#pragma once

#include "ofMain.h"

class testApp : public ofBaseApp{

  public:
		void setup();
};

ofSaveImage(foo.getPixelsRef(), imageBuffer, OF_IMAGE_FORMAT_JPEG, OF_IMAGE_QUALITY_BEST);