First public commit.

lenser/spectrum/palette.py

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+"""Sinclair ZX Spectrum colour palette.
+
+The ULA has 8 base colours, each in a normal and a BRIGHT version (component
+value 0xD7 normal, 0xFF bright; black is the same in both).  Crucially the BRIGHT
+bit is per 8x8 *cell*, shared by that cell's ink and paper -- so a cell's two
+colours must both be normal or both be bright (they can't mix).  We model this as
+a 16-entry palette: indices 0-7 = normal, 8-15 = bright, where index & 7 is the
+ink/paper colour number and index >> 3 is the BRIGHT bit.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ..palette import srgb_to_lab
+
+_N = 0xD7   # normal-brightness component
+_B = 0xFF   # bright component
+
+
+def _ramp(v):
+    # colour order matches the Spectrum's INK/PAPER numbering 0..7
+    return [
+        (0, 0, 0),     # 0 black
+        (0, 0, v),     # 1 blue
+        (v, 0, 0),     # 2 red
+        (v, 0, v),     # 3 magenta
+        (0, v, 0),     # 4 green
+        (0, v, v),     # 5 cyan
+        (v, v, 0),     # 6 yellow
+        (v, v, v),     # 7 white
+    ]
+
+
+SPECTRUM = np.array(_ramp(_N) + _ramp(_B), dtype=np.float64)
+
+# Cell colour pairs must come from one brightness group (shared BRIGHT bit).
+NORMAL_GROUP = list(range(0, 8))
+BRIGHT_GROUP = list(range(8, 16))
+
+
+def get_palette() -> np.ndarray:
+    return SPECTRUM
+
+
+def palette_lab() -> np.ndarray:
+    return srgb_to_lab(SPECTRUM)