title: Blur QImage alpha channel
body: <p>I'm trying to blur QImage alpha channel. My current implementation use deprecated 'alphaChannel' method and works slow.</p>
  
  <pre><code>QImage blurImage(const QImage &amp; image, double radius)
  {
    QImage newImage = image.convertToFormat(QImage::Format_ARGB32);
  
    QImage alpha = newImage.alphaChannel();
    QImage blurredAlpha = alpha;
    for (int x = 0; x &lt; alpha.width(); x++)
    {
      for (int y = 0; y &lt; alpha.height(); y++)
      {
        uint color = calculateAverageAlpha(x, y, alpha, radius);
        blurredAlpha.setPixel(x, y, color);
      }
    }
    newImage.setAlphaChannel(blurredAlpha);
  
    return newImage;
  }
  </code></pre>
  
  <p>I was also trying to implement it using QGraphicsBlurEffect, but it doesn't affect alpha.</p>
  
  <p>What is proper way to blur QImage alpha channel?</p>