<hue-interpolation-method>

The <hue-interpolation-method> CSS data type represents the algorithm used for interpolation between <hue> values. The interpolation method specifies how to find a midpoint between two hue values based on a color wheel. It is used as a component of the <color-interpolation-method> data type.

When interpolating <hue> values, the hue interpolation algorithm defaults to shorter.

Syntax

A <hue-interpolation-method> value consists of the name of a hue interpolation algorithm followed by a literal token hue:

shorter hue
longer hue
increasing hue
decreasing hue

Values

Any pair of hue angles correspond to two radii on the color wheel, which cut the circumference into two possible arcs for interpolation. Both arcs start at the first radius and end at the second radius, but one goes clockwise and the other goes counterclockwise.

Note: The following descriptions and illustrations are based on color wheels in which hue angles increase in a clockwise direction. Be aware that there are color wheels where an increase in angles will be a counterclockwise operation.

For a pair of hue angles θ1 and θ2 normalized to the range [0deg, 360deg), there are four algorithms to determine which arc is used when interpolating from θ1 to θ2:

shorter

Use the shorter arc. When the two radii coincide, the arc degenerates to a single point. When both arcs have the same lengths:

  • If θ1 < θ2, use the clockwise arc;
  • If θ1 > θ2, use the counterclockwise arc.
θ1 = 45deg, θ2 = 135deg θ1 = 135deg, θ2 = 45deg
shorter with θ1 = 45deg and θ2 = 135deg shorter with θ1 = 135deg and θ2 = 45deg
longer

Use the longer arc. When the two radii coincide:

  • If θ1 ≤ θ2, the arc becomes the full circumference with a clockwise orientation.
  • If θ1 > θ2, the arc becomes the full circumference with a counterclockwise orientation.

When both arcs have the same lengths:

  • If θ1 < θ2, use the clockwise arc;
  • If θ1 > θ2, use the counterclockwise arc.
θ1 = 45deg, θ2 = 135deg θ1 = 135deg, θ2 = 45deg
longer with θ1 = 45deg and θ2 = 135deg longer with θ1 = 135deg and θ2 = 45deg
increasing

Use the clockwise arc. When the two radii coincide, the arc degenerates to a single point.

θ1 = 45deg, θ2 = 135deg θ1 = 135deg, θ2 = 45deg
increasing with θ1 = 45deg and θ2 = 135deg increasing with θ1 = 135deg and θ2 = 45deg
decreasing

Use the counterclockwise arc. When the two radii coincide, the arc degenerates to a single point.

θ1 = 45deg, θ2 = 135deg θ1 = 135deg, θ2 = 45deg
decreasing with θ1 = 45deg and θ2 = 135deg decreasing with θ1 = 135deg and θ2 = 45deg

As there are only two arcs to choose from, these algorithms are pairwise equivalent under certain circumstances. Specifically:

  • If 0deg < θ2 - θ1 < 180deg or θ2 - θ1 < -180deg, shorter and increasing are equivalent, whereas longer and decreasing are equivalent.
  • If -180deg < θ2 - θ1 < 0deg or θ2 - θ1 > 180deg, shorter and decreasing are equivalent, whereas longer and increasing are equivalent.

A notable feature of increasing and decreasing is that when the hue angle difference passes through 180deg during transition or animation, the arc will not flip to the other side like shorter and longer do.

Formal syntax

<hue-interpolation-method> = 
[ shorter | longer | increasing | decreasing ] hue

Examples

Comparing hue interpolation algorithms

The following example shows the effect of using different hue interpolation algorithms in a linear-gradient().

HTML

html
<div class="hsl">
  <p>HSL</p>
</div>
<div class="hsl-increasing">
  <p>HSL increasing</p>
</div>
<div class="hsl-decreasing">
  <p>HSL decreasing</p>
</div>
<div class="hsl-shorter">
  <p>HSL shorter</p>
</div>
<div class="hsl-longer">
  <p>HSL longer</p>
</div>
<div class="hsl-named">
  <p>HSL named</p>
</div>
<div class="hsl-named-longer">
  <p>HSL named (longer)</p>
</div>

CSS

css
.hsl {
  background: linear-gradient(
    to right in hsl,
    hsl(39deg 100% 50%),
    hsl(60deg 100% 50%)
  );
}
.hsl-increasing {
  background: linear-gradient(
    to right in hsl increasing hue,
    hsl(190deg 100% 50%),
    hsl(180deg 100% 50%)
  );
}
.hsl-decreasing {
  background: linear-gradient(
    to right in hsl decreasing hue,
    hsl(39deg 100% 50%),
    hsl(60deg 100% 50%)
  );
}
.hsl-shorter {
  background: linear-gradient(
    to right in hsl shorter hue,
    hsl(39deg 100% 50%),
    hsl(60deg 100% 50%)
  );
}
.hsl-longer {
  background: linear-gradient(
    to right in hsl longer hue,
    hsl(39deg 100% 50%),
    hsl(60deg 100% 50%)
  );
}
.hsl-named {
  background: linear-gradient(to right in hsl, orange, yellow);
}
.hsl-named-longer {
  background: linear-gradient(to right in hsl longer hue, orange, yellow);
}

Result

Specifications

Specification
CSS Color Module Level 4
# hue-interpolation

Browser compatibility

css.types.color.color-mix

BCD tables only load in the browser

css.types.image.gradient.conic-gradient.hue_interpolation_method

BCD tables only load in the browser

css.types.image.gradient.linear-gradient.hue_interpolation_method

BCD tables only load in the browser

css.types.image.gradient.radial-gradient.hue_interpolation_method

BCD tables only load in the browser

css.types.image.gradient.repeating-conic-gradient.hue_interpolation_method

BCD tables only load in the browser

css.types.image.gradient.repeating-linear-gradient.hue_interpolation_method

BCD tables only load in the browser

css.types.image.gradient.repeating-radial-gradient.hue_interpolation_method

BCD tables only load in the browser

See also