title: Unable to export an Altair Plot directly to .png
body: <p>I'm currently unable to save an Altair plot I've produced as a <em>.png</em>. I'm trying to export the plot as an image so that I can embed it directly into an outlook email. The two methods I've tried are:</p>
  <ol>
  <li><p>Using built-in <code>alt.chart.save()</code> with an <code>embed_option</code> of <code>'renderer'</code> as <em>png</em>:</p>
  <p><code>((hours &amp; oilp &amp; wear &amp; viscos &amp; chart).resolve_scale(x='shared', color='independent')&amp; (bars)).save(&quot;Chart.png&quot;, embed_options={'renderer':'png'})</code></p>
  </li>
  <li><p>Using <code>altair_saver.save()</code> with the <em>.png</em> extension:</p>
  <p><code>altair_saver.save(((hours &amp; oilp &amp; wear &amp; viscos &amp; chart).resolve_scale(x='shared', color='independent') &amp; (bars)),&quot;Chart.png&quot;)</code></p>
  </li>
  </ol>
  <p>I've followed <a href="https://iliatimofeev.github.io/altair-viz.github.io/user_guide/saving_charts.html" rel="nofollow noreferrer">this link</a> and installed selenium and chromedriver using the anaconda cmd as it appears to interpret the Vega-lite extension in a browser then export in the form of an image.</p>
  <p>The error I receive is as below:</p>
  <pre><code>C:\Users\\Anaconda3\lib\site-packages\altair_saver\_core.py in _select_saver(method, mode, fmt, fp)
       67     else:
       68         raise ValueError(f&quot;Unrecognized method: {method}&quot;)
  ---&gt; 69 
       70     spec: JSONDict = {}
       71     if isinstance(chart, dict):
  
  ValueError: No enabled saver found that supports format='png'
  </code></pre>
  <p>Has anyone had any experience with this error or may be to provide a solution?</p>
  <p>Also is it possible to embed a vega HTML output directly into the body of an Outlook email with full hover over functionality? I anticipate that Outlook will not be equipped with the necessary rendering capabilities.</p>