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W3C Candidate Recommendation


Defines the alpha channel threshold used to extract a shape from an image. Can be thought of as a "minimum opacity" threshold; that is, a value of 0.5 means that the shape will enclose all the pixels that are more than 50% opaque.

Overview table

Initial value 0.0
Applies to Floats
Inherited No
Media visual
Computed value As specified, clamped to a 0.0-1.0 range
Animatable Yes
CSS Object Model Property
Percentages [[CSS percentages::Alpha channel of the image specified by shape-outside.]]


  • shape-image-threshold: <number>


A numeric value used to set the opacity threshold used for extracting a shape from an image. Any values outside the range 0.0 (fully transparent) to 1.0 (fully opaque) will be clamped to this range.


Note: Depends upon an image previously specified by shape-outside.


Extract a shape from an image by enclosing all pixels greater than 25% opacity
#myimg {
  shape-image-threshold: 0.25;

View live example


 Currently implemented as an experimental feature in WebKit and Blink. This can be used with a -webkit- prefix in WebKit nightly builds and with a -webkit- prefix in Chrome Canary builds with experimental-webkit-features enabled: chrome://flags/#enable-experimental-webkit-features

Related specifications

Specification Status Related Changes
CSS Shapes Module Level 1 W3C Candidate Recommendation

See also

Other articles

shape-outside shape-margin