Fix an incorrect formula for Q in the sCAM model.

Replace the exponent with recommended 0.1 instead of 0.46 and update test cases.

Closes #1360

Author: Jackchou00

colour/appearance/scam.py

@@ -264,7 +264,7 @@ def XYZ_to_sCAM(
     >>> surround = VIEWING_CONDITIONS_sCAM["Average"]
     >>> XYZ_to_sCAM(XYZ, XYZ_w, L_A, Y_b, surround)  # doctest: +ELLIPSIS
     CAM_Specification_sCAM(J=49.9795668..., C=0.0140531..., h=328.2724924..., \
-Q=206.4275827..., M=0.0050244..., H=363.6013437..., HC=None, V=49.9795727..., \
+Q=195.23024234..., M=0.0050244..., H=363.6013437..., HC=None, V=49.9795727..., \
 K=50.0204272..., W=34.9734327..., D=65.0265672...)
     """
 
@@ -302,7 +302,10 @@ def XYZ_to_sCAM(
 
     with sdiv_mode():
         M = (C * spow(F_L, 0.1) * sdiv(1, spow(I_a, 0.27)) * e_t) * surround.F
-        Q = sdiv(2, surround.c) * I_a * spow(F_L, 0.46)
+        # The original paper contained two inconsistent formulas for calculating Q:
+        # Equation (15) on page 6 uses an exponent of 0.1, while page 10 uses 0.46.
+        # After confirmation with the author, 0.1 is the recommended value.
+        Q = sdiv(2, surround.c) * I_a * spow(F_L, 0.1)
 
     H = hue_quadrature(h)
 

colour/appearance/tests/test_scam.py

@@ -56,7 +56,7 @@ def test_XYZ_to_sCAM(self) -> None:
                     49.97956680,
                     0.01405311,
                     328.27249244,
-                    206.42758274,
+                    195.23024234,
                     0.00502448,
                     363.60134377,
                     np.nan,
@@ -78,7 +78,7 @@ def test_XYZ_to_sCAM(self) -> None:
                     71.63079886,
                     37.33838127,
                     18.75135858,
-                    207.84501305,
+                    259.13174065,
                     10.66713872,
                     4.20415978,
                     np.nan,
@@ -101,7 +101,7 @@ def test_XYZ_to_sCAM(self) -> None:
                     29.61821869,
                     25.97461207,
                     178.56952253,
-                    122.33033780,
+                    115.69472052,
                     10.76901611,
                     227.46922207,
                     np.nan,