Add sUCS and use the same D65 white point as ITP

Author: facelessuser

coloraide/everything.py

@@ -33,6 +33,7 @@
 from .spaces.hellwig import HellwigJMh, HellwigHKJMh
 from .spaces.zcam import ZCAMJMh
 from .spaces.scam import sCAMJMh
+from .spaces.sucs import sUCS
 from .spaces.hct import HCT
 from .spaces.ucs import UCS
 from .spaces.rec709 import Rec709
@@ -103,6 +104,7 @@ class ColorAll(Base):
         Cubehelix(),
         ZCAMJMh(),
         sCAMJMh(),
+        sUCS(),
 
         # Delta E
         DE99o(),

coloraide/spaces/ipt.py

@@ -11,6 +11,8 @@
 from .. import util
 from ..types import Vector
 
+D65 = tuple(util.xyz_to_xyY([0.9504, 1.0, 1.0889])[:-1])  # type: tuple[float, float]  # type: ignore[assignment]
+
 # IPT matrices for LMS conversion with better accuracy for 64 bit doubles
 XYZ_TO_LMS = [
     [0.40021823485770675, 0.7075142362766385, -0.08070681117219487],
@@ -71,7 +73,7 @@ class IPT(Lab):
     # The D65 white point used in the paper was different than what we use.
     # We use chromaticity points (0.31270, 0.3290) which gives us an XYZ of ~[0.9505, 1.0000, 1.0890]
     # IPT uses XYZ of [0.9504, 1.0, 1.0889] which yields chromaticity points ~(0.3127035830618893, 0.32902313032606195)
-    WHITE = tuple(util.xyz_to_xyY([0.9504, 1.0, 1.0889])[:-1])  # type: ignore[assignment]
+    WHITE = D65
 
     def lightness_name(self) -> str:
         """Get lightness name."""

coloraide/spaces/scam.py

@@ -8,26 +8,11 @@
 from .. import util
 from .. import algebra as alg
 from .lch import LCh
-from ..cat import WHITES
 from ..channels import Channel, FLG_ANGLE
-from ..types import Vector, VectorLike
 from .cam16 import hue_quadrature, inv_hue_quadrature, M16, M16_INV
-
-# LMS matrices
-TO_LMS = [
-    [0.4002, 0.7075, -0.0807],
-    [-0.2280, 1.1500, 0.0612],
-    [0.0000, 0.0000, 0.9184],
-]
-FROM_LMS = alg.inv(TO_LMS)
-
-# Iab transformation matrices
-TO_IAB = [
-    alg.divide([200.0, 100.0, 5.0], 3.05, dims=alg.D1_SC),
-    [430.0, -470.0, 40.0],
-    [49.0, 49.0, -98.0]
-]
-FROM_IAB = alg.inv(TO_IAB)
+from .sucs import xyz_to_sucs, sucs_to_xyz
+from .ipt import D65
+from ..types import Vector, VectorLike
 
 SURROUND = {
     'dark': (0.39, 0.85),
@@ -128,7 +113,7 @@ def __init__(
         self.yw = self.input_white[1]
         # Destination luminance
         self.output_white = alg.multiply_x3(
-            util.xy_to_xyz(WHITES['2deg']['D65']),
+            util.xy_to_xyz(D65),
             (self.la * 100) / self.yb,
             dims=alg.D1_SC
         )
@@ -145,27 +130,6 @@ def __init__(
         self.d = alg.clamp(self.fm * (1 - 1 / 3.6 * math.exp((-self.la - 42) / 92)), 0, 1) if not discounting else 1
 
 
-def sucs_to_xyz(ich: Vector) -> Vector:
-    """From sUCS to XYZ."""
-
-    i, c, h = ich
-    c = (math.exp(0.0252 * c) - 1) / 0.0447
-    r = math.radians(h)
-    a, b = c * math.cos(r), c * math.sin(r)
-    lms = [alg.nth_root(x, 0.43) for x in alg.matmul_x3(FROM_IAB, [i, a, b], dims=alg.D2_D1)]
-    return alg.matmul_x3(FROM_LMS, lms, dims=alg.D2_D1)
-
-
-def xyz_to_sucs(xyz: Vector) -> Vector:
-    """From XYZ to sUCS."""
-
-    lms_p = [math.copysign(abs(i) ** 0.43, i) for i in alg.matmul_x3(TO_LMS, xyz, dims=alg.D2_D1)]
-    i, a, b = alg.matmul_x3(TO_IAB, lms_p, dims=alg.D2_D1)
-    c = (1 / 0.0252) * math.log(1 + 0.0447 * math.sqrt(a ** 2 + b ** 2))
-    h = math.atan2(b, a) % math.tau
-    return [i, c, math.degrees(h)]
-
-
 def scam_to_xyz(
     J: float | None = None,
     C: float | None = None,
@@ -233,12 +197,15 @@ def scam_to_xyz(
 
     # Convert to XYZ from sUCS
     xyz = sucs_to_xyz([I, C, h])  # type: ignore[list-item]
+
+    # Apply chromatic adaptation
     return adapt(xyz, env.output_white, env.input_white, env.d)
 
 
 def xyz_to_scam(xyz: Vector, env: Environment, calc_hue_quadrature: bool = True) -> Vector:
     """From XYZ to sCAM."""
 
+    # Apply chromatic adaptation
     xyz = adapt(xyz, env.input_white, env.output_white, env.d)
 
     # Convert from XYZ to sUCS
@@ -299,7 +266,8 @@ class sCAMJMh(LCh):
         "colorfulness": 'm',
         "hue": 'h'
     }
-    WHITE = WHITES['2deg']['D65']
+    # WHITE = tuple(util.xyz_to_xyY([0.9504, 1.0, 1.0889])[:-1])
+    WHITE = D65
     # Assuming sRGB which has a lux of 64: `((E * R) / PI) / 5` where `R = 1`.
     ENV = Environment(
         # Our white point.
@@ -315,7 +283,7 @@ class sCAMJMh(LCh):
         discounting=False
     )
     CHANNELS = (
-        Channel("j", 0.0, 99.999),
+        Channel("j", 0.0, 100.0),
         Channel("m", 0, 25.0),
         Channel("h", 0.0, 360.0, flags=FLG_ANGLE)
     )

coloraide/spaces/sucs.py

@@ -0,0 +1,85 @@
+"""
+Simple Color Appearance Model (sUCS).
+
+https://opg.optica.org/oe/fulltext.cfm?uri=oe-32-3-3100&id=545619
+"""
+from __future__ import annotations
+import math
+from .. import util
+from .. import algebra as alg
+from .lch import LCh
+from ..cat import WHITES
+from ..channels import Channel, FLG_ANGLE
+from ..types import Vector
+from .ipt import XYZ_TO_LMS, LMS_TO_XYZ, D65
+
+# Iab transformation matrices
+TO_IAB = [
+    alg.divide([200.0, 100.0, 5.0], 3.05, dims=alg.D1_SC),
+    [430.0, -470.0, 40.0],
+    [49.0, 49.0, -98.0]
+]
+FROM_IAB = alg.inv(TO_IAB)
+
+
+def sucs_to_xyz(ich: Vector) -> Vector:
+    """From sUCS to XYZ."""
+
+    i, c, h = ich
+    c = (math.exp(0.0252 * c) - 1) / 0.0447
+    r = math.radians(h)
+    a, b = c * math.cos(r), c * math.sin(r)
+    lms = [alg.nth_root(x, 0.43) for x in alg.matmul_x3(FROM_IAB, [i, a, b], dims=alg.D2_D1)]
+    return alg.matmul_x3(LMS_TO_XYZ, lms, dims=alg.D2_D1)
+
+
+def xyz_to_sucs(xyz: Vector) -> Vector:
+    """From XYZ to sUCS."""
+
+    lms_p = [math.copysign(abs(i) ** 0.43, i) for i in alg.matmul_x3(XYZ_TO_LMS, xyz, dims=alg.D2_D1)]
+    i, a, b = alg.matmul_x3(TO_IAB, lms_p, dims=alg.D2_D1)
+    c = (1 / 0.0252) * math.log(1 + 0.0447 * math.sqrt(a ** 2 + b ** 2))
+    h = math.atan2(b, a) % math.tau
+    return [i, c, math.degrees(h)]
+
+
+class sUCS(LCh):
+    """sUCS class (JMh)."""
+
+    BASE = "xyz-d65"
+    NAME = "sucs"
+    SERIALIZE = ("--sucs",)
+    CHANNEL_ALIASES = {
+        "lightness": "i",
+        "chroma": 'c',
+        "hue": 'h'
+    }
+    WHITE = D65
+    CHANNELS = (
+        Channel("i", 0.0, 100),
+        Channel("c", 0, 65.0),
+        Channel("h", 0.0, 360.0, flags=FLG_ANGLE)
+    )
+
+    def lightness_name(self) -> str:
+        """Get lightness name."""
+
+        return "i"
+
+    def normalize(self, coords: Vector) -> Vector:
+        """Normalize."""
+
+        if coords[1] < 0.0:
+            return self.from_base(self.to_base(coords))
+        coords[2] %= 360.0
+        return coords
+
+    def to_base(self, coords: Vector) -> Vector:
+        """From sCAM JMh to XYZ."""
+
+        return sucs_to_xyz(coords)
+
+    def from_base(self, coords: Vector) -> Vector:
+        """From XYZ to sCAM JMh."""
+
+        return xyz_to_sucs(coords)