Handle achromatic threshold better (#462)

Spaces that are scaled on an order of magnitude of 1 should not have the
same threshold of a space scaled at an order of magnitude of 100. If
they are, this can cause colors to be considered achromatic much
earlier if they are scaled small.

Author: facelessuser

coloraide/average.py

@@ -1,6 +1,7 @@
 """Average colors together."""
 from __future__ import annotations
 import math
+from . import util
 from .spaces import HWBish
 from .types import ColorInput
 from typing import Iterable, TYPE_CHECKING
@@ -9,9 +10,6 @@
     from .color import Color
 
 
-ACHROMATIC_THRESHOLD = 1e-4
-
-
 def average(
     color_cls: type[Color],
     colors: Iterable[ColorInput],
@@ -88,7 +86,7 @@ def average(
             else:
                 sin /= total
                 cos /= total
-            if abs(sin) < ACHROMATIC_THRESHOLD and abs(cos) < ACHROMATIC_THRESHOLD:
+            if abs(sin) < util.ACHROMATIC_THRESHOLD_SM and abs(cos) < util.ACHROMATIC_THRESHOLD_SM:
                 sums[i] = math.nan
             else:
                 avg_theta = math.degrees(math.atan2(sin, cos))

coloraide/spaces/cam16_jmh.py

@@ -12,10 +12,9 @@
 import bisect
 from .. import util
 from .. import algebra as alg
-from ..spaces import Space, LChish
+from .lch import LCh
 from ..cat import WHITES, CAT16
 from ..channels import Channel, FLG_ANGLE
-from .lch import ACHROMATIC_THRESHOLD
 from ..types import Vector, VectorLike
 
 # CAT16
@@ -352,7 +351,7 @@ def cam_jmh_to_xyz(jmh: Vector, env: Environment) -> Vector:
     return cam_to_xyz(J=J, M=M, h=h, env=env)
 
 
-class CAM16JMh(LChish, Space):
+class CAM16JMh(LCh):
     """CAM16 class (JMh)."""
 
     BASE = "xyz-d65"
@@ -396,7 +395,7 @@ def is_achromatic(self, coords: Vector) -> bool | None:
         """Check if color is achromatic."""
 
         # Account for both positive and negative chroma
-        return coords[0] == 0 or abs(coords[1]) < ACHROMATIC_THRESHOLD
+        return coords[0] == 0 or abs(coords[1]) < self.achromatic_threshold
 
     def to_base(self, coords: Vector) -> Vector:
         """From CAM16 JMh to XYZ."""

coloraide/spaces/cam16_ucs.py

@@ -8,8 +8,7 @@
 from __future__ import annotations
 import math
 from .cam16_jmh import CAM16JMh, xyz_to_cam, cam_to_xyz, Environment
-from ..spaces import Space, Labish
-from .lch import ACHROMATIC_THRESHOLD
+from .lab import Lab
 from ..cat import WHITES
 from .. import util
 from ..channels import Channel, FLG_MIRROR_PERCENT
@@ -91,7 +90,7 @@ def cam_ucs_to_cam_jmh(ucs: Vector, model: str) -> Vector:
     ]
 
 
-class CAM16UCS(Labish, Space):
+class CAM16UCS(Lab):
     """CAM16 UCS (Jab) class."""
 
     BASE = "cam16-jmh"
@@ -114,7 +113,7 @@ def is_achromatic(self, coords: Vector) -> bool:
         """Check if color is achromatic."""
 
         j, m = cam_ucs_to_cam_jmh(coords, self.MODEL)[:-1]
-        return j == 0 or abs(m) < ACHROMATIC_THRESHOLD
+        return j == 0 or abs(m) < self.achromatic_threshold
 
     def to_base(self, coords: Vector) -> Vector:
         """To CAM16 JMh from CAM16."""

coloraide/spaces/cmy.py

@@ -1,5 +1,6 @@
 """Uncalibrated, naive CMY color space."""
 from __future__ import annotations
+from .. import util
 from ..spaces import Regular, Space
 from ..channels import Channel
 from ..cat import WHITES
@@ -43,7 +44,7 @@ def is_achromatic(self, coords: Vector) -> bool:
 
         black = [1, 1, 1]
         for x in alg.vcross(coords, black):
-            if not math.isclose(0.0, x, abs_tol=1e-4):
+            if not math.isclose(0.0, x, abs_tol=util.ACHROMATIC_THRESHOLD_SM):
                 return False
         return True
 

coloraide/spaces/cmyk.py

@@ -4,6 +4,7 @@
 https://www.w3.org/TR/css-color-5/#cmyk-rgb
 """
 from __future__ import annotations
+from .. import util
 from ..spaces import Space
 from ..channels import Channel
 from ..cat import WHITES
@@ -60,12 +61,12 @@ class CMYK(Space):
     def is_achromatic(self, coords: Vector) -> bool:
         """Test if color is achromatic."""
 
-        if math.isclose(1.0, coords[-1], abs_tol=1e-4):
+        if math.isclose(1.0, coords[-1], abs_tol=util.ACHROMATIC_THRESHOLD_SM):
             return True
 
         black = [1, 1, 1]
         for x in alg.vcross(coords[:-1], black):
-            if not math.isclose(0.0, x, abs_tol=1e-5):
+            if not math.isclose(0.0, x, abs_tol=util.ACHROMATIC_THRESHOLD_SM):
                 return False
         return True
 

coloraide/spaces/cubehelix.py

@@ -24,7 +24,7 @@
 THIS SOFTWARE.
 """
 from __future__ import annotations
-from ..spaces import Space, HSLish
+from . hsl import HSL
 from ..cat import WHITES
 from ..channels import Channel, FLG_ANGLE
 import math
@@ -72,7 +72,7 @@ def cubehelix_to_srgb(coords: Vector) -> Vector:
     ]
 
 
-class Cubehelix(HSLish, Space):
+class Cubehelix(HSL):
     """Cubehelix class."""
 
     BASE = 'srgb'
@@ -103,7 +103,7 @@ def normalize(self, coords: Vector) -> Vector:
     def is_achromatic(self, coords: Vector) -> bool:
         """Check if color is achromatic."""
 
-        return abs(coords[1]) < 1e-4 or coords[2] > (1 - 1e-7) or coords[2] < 1e-08
+        return abs(coords[1]) < self.achromatic_threshold or coords[2] > (1 - 1e-7) or coords[2] < 1e-08
 
     def to_base(self, coords: Vector) -> Vector:
         """To LChuv from HSLuv."""

coloraide/spaces/hct.py

@@ -38,12 +38,11 @@
 """
 from __future__ import annotations
 from .. import algebra as alg
-from ..spaces import Space, LChish
+from .lch import LCh
 from ..cat import WHITES
 from ..channels import Channel, FLG_ANGLE
 from .cam16_jmh import Environment, cam_to_xyz, xyz_to_cam
 from .lab import EPSILON, KAPPA, KE
-from .lch import ACHROMATIC_THRESHOLD
 from ..types import Vector
 import math
 
@@ -156,7 +155,7 @@ def xyz_to_hct(coords: Vector, env: Environment) -> Vector:
     return [h, c, t]
 
 
-class HCT(LChish, Space):
+class HCT(LCh):
     """HCT class."""
 
     BASE = "xyz-d65"
@@ -200,7 +199,7 @@ def is_achromatic(self, coords: Vector) -> bool | None:
         """Check if color is achromatic."""
 
         # Account for both positive and negative chroma
-        return coords[2] == 0 or abs(coords[1]) < ACHROMATIC_THRESHOLD
+        return coords[2] == 0 or abs(coords[1]) < self.achromatic_threshold
 
     def names(self) -> tuple[Channel, ...]:
         """Return LCh-ish names in the order L C h."""

coloraide/spaces/hpluv.py

@@ -25,7 +25,7 @@
 SOFTWARE.
 """
 from __future__ import annotations
-from ..spaces import Space, HSLish
+from .hsl import HSL
 from ..cat import WHITES
 from ..channels import Channel, FLG_ANGLE
 from .lab import EPSILON, KAPPA
@@ -103,7 +103,7 @@ def luv_to_hpluv(luv: Vector) -> Vector:
     return [util.constrain_hue(h), s, l]
 
 
-class HPLuv(HSLish, Space):
+class HPLuv(HSL):
     """HPLuv class."""
 
     BASE = 'luv'
@@ -120,6 +120,7 @@ class HPLuv(HSLish, Space):
         "lightness": "l"
     }
     WHITE = WHITES['2deg']['D65']
+    GAMUT_CHECK = None
 
     def normalize(self, coords: Vector) -> Vector:
         """Normalize coordinates."""
@@ -132,7 +133,7 @@ def normalize(self, coords: Vector) -> Vector:
     def is_achromatic(self, coords: Vector) -> bool:
         """Check if color is achromatic."""
 
-        return abs(coords[1]) < 1e-4 or coords[2] > (100 - 1e-7) or coords[2] < 1e-08
+        return abs(coords[1]) < self.achromatic_threshold or coords[2] > (100 - 1e-7) or coords[2] < 1e-08
 
     def to_base(self, coords: Vector) -> Vector:
         """To LChuv from HPLuv."""

coloraide/spaces/hsl/__init__.py

@@ -1,10 +1,12 @@
 """HSL class."""
 from __future__ import annotations
+from ... import algebra as alg
 from ...spaces import HSLish, Space
 from ...cat import WHITES
 from ...channels import Channel, FLG_ANGLE
 from ... import util
 from ...types import Vector
+from typing import Any
 
 
 def srgb_to_hsl(rgb: Vector) -> Vector:
@@ -82,6 +84,13 @@ class HSL(HSLish, Space):
     GAMUT_CHECK = "srgb"  # type: str | None
     CLIP_SPACE = "hsl"  # type: str | None
 
+    def __init__(self, **kwargs: Any):
+        """Initialize."""
+
+        super().__init__(**kwargs)
+        order = alg.order(self.channels[self.indexes()[2]].high)
+        self.achromatic_threshold = util.ACHROMATIC_THRESHOLD_SM if order == 0 else util.ACHROMATIC_THRESHOLD
+
     def normalize(self, coords: Vector) -> Vector:
         """Normalize coordinates."""
 
@@ -94,7 +103,11 @@ def normalize(self, coords: Vector) -> Vector:
     def is_achromatic(self, coords: Vector) -> bool | None:
         """Check if color is achromatic."""
 
-        return abs(coords[1]) < 1e-4 or coords[2] == 0.0 or abs(1 - coords[2]) < 1e-7
+        return (
+            abs(coords[1]) < self.achromatic_threshold or
+            coords[2] == 0.0 or
+            abs(1 - coords[2]) < self.achromatic_threshold
+        )
 
     def to_base(self, coords: Vector) -> Vector:
         """To sRGB from HSL."""

coloraide/spaces/hsluv.py

@@ -25,9 +25,9 @@
 SOFTWARE.
 """
 from __future__ import annotations
-from ..spaces import Space, HSLish
 from ..cat import WHITES
 from ..channels import Channel, FLG_ANGLE
+from .hsl import HSL
 from .lab import EPSILON, KAPPA
 from .srgb_linear import XYZ_TO_RGB
 import math
@@ -106,7 +106,7 @@ def luv_to_hsluv(luv: Vector) -> Vector:
     return [util.constrain_hue(h), s, l]
 
 
-class HSLuv(HSLish, Space):
+class HSLuv(HSL):
     """HSLuv class."""
 
     BASE = 'luv'
@@ -137,7 +137,7 @@ def normalize(self, coords: Vector) -> Vector:
     def is_achromatic(self, coords: Vector) -> bool:
         """Check if color is achromatic."""
 
-        return abs(coords[1]) < 1e-4 or coords[2] > (100 - 1e-7) or coords[2] < 1e-08
+        return abs(coords[1]) < self.achromatic_threshold or coords[2] > (100 - 1e-7) or coords[2] < 1e-08
 
     def to_base(self, coords: Vector) -> Vector:
         """To LChuv from HSLuv."""