title: How to convert in-place batch of PNG from grayscale to RGB?
body: <p>So, I want to convert many PNGs from grayscale to RGB, similar to <a href="https://stackoverflow.com/questions/34874771/convert-jpg-image-from-grayscale-to-rgb-using-imagemagick">this question</a></p>
  
  <p>However, the given command there does not work for PNGs. Moreover, that is <code>convert</code> and I read that to process images <em>in-place</em> one would have to use <code>mogrify</code>. How can I use this?</p>