First public commit.

lenser/spectrum/convert/mono.py

@@ -0,0 +1,47 @@
+"""ZX Spectrum monochrome / tinted-mono mode.
+
+256x192 matched by luminance.  The Spectrum has no grey, so greyscale is a 2-level
+black/white halftone (bright black + bright white) -- which at 256x192 with
+dithering is a crisp, high-detail image free of attribute clash.  A base colour
+gives a 3-level tinted ramp (black -> colour -> white), all within one brightness
+group so the per-cell BRIGHT constraint is satisfied.  Reuses the hires packing.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ...convert import base
+from .. import palette as spal
+from . import hires
+
+
+def _ramp(base_color):
+    """Luminance ramp kept inside ONE brightness group (shared BRIGHT bit)."""
+    if base_color is None:
+        return [8, 15]                       # bright black + bright white
+    c = base_color & 7                        # base hue 0-7
+    if c in (0, 7):
+        return [8, 15]
+    return [8, 8 | c, 15]                      # bright black, bright hue, bright white
+
+
+def convert(img_rgb, palette_name="spectrum", dither_mode="atkinson",
+            intensive=False, base_color=None):
+    plab = spal.palette_lab()
+    prgb = spal.get_palette().astype(np.uint8)
+    ramp = _ramp(base_color)
+
+    idx, sets, rows, cols, err = base.mono_render(
+        img_rgb, plab, ramp, hires.WIDTH, hires.HEIGHT,
+        hires.CELL_W, hires.CELL_H, dither_mode, n_free=2)
+
+    scr = hires._encode(idx, sets, rows, cols)
+
+    return base.Conversion(
+        mode="mono", width=hires.WIDTH, height=hires.HEIGHT,
+        pixel_aspect=hires.PIXEL_ASPECT, index_image=idx.astype(np.uint16),
+        data=bytes(scr), data_addr=0x4000, viewer="spectrum", preview_rgb=prgb[idx],
+        error=err,
+        meta={"palette": "spectrum", "dither": dither_mode, "base_color": base_color},
+    )