title: Imagemagick: Convert to fixed height, proportional width
body: <p>Using Imagemagick, I'd like to <code>convert</code> a batch of PNGs to a fixed height of 1080px and a <em>proportional width</em>. With <em>proportional</em> I mean this: If the original Image is scaled down 16.8% to 1080px, the width also needs to be scaled down by 16.8%.</p>
  
  <p>Any way of using convert without having to calculate the exact geometry before (using <code>identify</code> and some bash calculation shenanigans) ?</p>