保持Alpha

html,
body,
svg {
  height: 100%;
}

<svg viewBox="0 0 420 200" xmlns="http://www.w3.org/2000/svg">
  <filter id="convolveMatrix1" x="0" y="0" width="100%" height="100%">
    <feConvolveMatrix kernelMatrix="1 -1 2 0 0 0 0 0 -2" preserveAlpha="true" />
  </filter>
  <filter id="convolveMatrix2" x="0" y="0" width="100%" height="100%">
    <feConvolveMatrix
      kernelMatrix="1 -1 2 0 0 0 0 0 -2"
      preserveAlpha="false" />
  </filter>

  <image
    href="mdn_logo_only_color.png"
    width="200"
    height="200"
    filter="url(#convolveMatrix1)" />
  <image
    x="220"
    href="mdn_logo_only_color.png"
    width="200"
    height="200"
    filter="url(#convolveMatrix2)" />
</svg>