title: Konvajs Grayscale turn off
body: <p>I am using Konvajs filters to give the user the ability to change brightness, contrast and grayscale of the image.
  As per the KonvaJs examples I am using input sliders which works great.
  For Brightness and Contrast I am using:</p>
  <pre><code>image.filters([Konva.Filters.Brighten, Konva.Filters.Contrast]);
  </code></pre>
  <p>But for Grayscale I am using input slider as an on/off switch and the following filter:</p>
  <pre><code>image.filters([Konva.Filters.Grayscale]);
  </code></pre>
  <p>So when the users sets the Grayscale switch to &quot;on&quot; I can invoke the Grayscale filter.
  But if the user then switches Grayscale to &quot;off&quot; there doesn't seem to be a way of cancelling this filter.</p>
  <p>I have a workaround that involves cancelling ALL filters:</p>
  <pre><code>image.filters([]);
  </code></pre>
  <p>And then re-invoking the brightness and contrast filters to the value previously set.
  Is there a way to simply cancel the Grayscale filter?</p>