title: Animate image's saturation
body: <p>Is it possible to animate the saturation of an image (e.g. png) over time? For example from grayscale to full color. Plus if I can use an Interpolator.</p>
  
  <p>I have seen the EffectFactory and the ColorMatrix classes but I cannot combine them with an animation/transition.</p>
  
  <p>E.g. applying grayscale saturation on a <code>Drawable drawable</code>:</p>
  
  <pre><code>ColorMatrix matrix = new ColorMatrix();
  matrix.setSaturation(0);
  
  ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrix);
  drawable.setColorFilter(filter);
  </code></pre>
  
  <p>and for full saturation later:</p>
  
  <pre><code>matrix.setSaturation(1);
  </code></pre>
  
  <hr>
  
  <p>For anyone interested my full solution based on Simon's answer:</p>
  
  <pre><code>final ColorMatrix matrix = new ColorMatrix();
  final Drawable drawable = ... ;
  
  ValueAnimator animation = ValueAnimator.ofFloat(0f, 1f);
  animation.setDuration(1000);
  //   animation.setInterpolator();
  animation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
      @Override
      public void onAnimationUpdate(ValueAnimator animation) {
          matrix.setSaturation(animation.getAnimatedFraction());
          ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrix);
          drawable.setColorFilter(filter);
      }
  });
  animation.start();
  </code></pre>