The shape-image-threshold CSS property defines the alpha channel threshold used to extract the shape using an image.
object.style.shapeImageThreshold = "value";
<'shape-image-threshold'> = <alpha-value>
<alpha-value> = <number> | <percentage>
An integer or zero or more decimal digits followed by a dot (.) followed by one or more decimal digits. The first character may be preceded by a sign (- or +). The last character may be succeeded by an exponent (e or E) and an integer.
Specifies the percentage using a number followed by a percent sign (%).