const originalRatios = {
      width: window.innerWidth / imgBackground.width,
      height: window.innerHeight / imgBackground.height
    };

const coverRatio = Math.max(originalRatios.width, originalRatios.height);
const newImageWidth = imgBackground.width * coverRatio;
const newImageHeight = imgBackground.height * coverRatio;

//Draw image centered
image(imgBackground, width / 2 - newImageWidth / 2, height / 2 - newImageHeight / 2, newImageWidth, newImageHeight);