preserveAlpha

the preserveAlpha attribute indicates how a <feConvolveMatrix> element handled alpha transparency.

Only one element is using this attribute: <feConvolveMatrix>

<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 xlink:href="//developer.mozilla.org/files/6457/mdn_logo_only_color.png" width="200" height="200"
      style="filter:url(#convolveMatrix1);"/>
  <image xlink:href="//developer.mozilla.org/files/6457/mdn_logo_only_color.png" width="200" height="200"
      style="filter:url(#convolveMatrix2); transform:translateX(220px);"/>
</svg>

Usage notes

Default value	`false`
Value	`true` \| `false`
Animatable	Yes

true: This value indicates that the convolution will only apply to the color channels. In this case, the filter will temporarily unpremultiply the color component values and apply the kernel.
false: This value indicates that the convolution will apply to all channels, including the alpha channel.

Specifications

Specification	Status	Comment
Filter Effects Module Level 1 The definition of 'preserveAlpha' in that specification.	Working Draft	No change
Scalable Vector Graphics (SVG) 1.1 (Second Edition) The definition of 'preserveAlpha' in that specification.	Recommendation	Initial definition

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