First public commit.

lenser/a7800/convert/mono.py

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+"""Atari 7800 monochrome / tinted-mono (MARIA 160A restricted to one hue).
+
+Reuses the c160 machinery but restricts the colour pool to the 16 luminances of a
+single hue (hue 0 = greyscale), so the 8 palettes become up to ~16 grey levels and
+the per-segment palette choice yields a smooth, detailed luminance image.
+"""
+from __future__ import annotations
+
+import numpy as np
+
+from ... import palette as c64pal
+from ...convert.base import DIFFUSION_DITHERS, perceptual_error
+from ...atari import palette as apal
+from . import c160
+
+WIDTH, HEIGHT, PIXEL_ASPECT = c160.WIDTH, c160.HEIGHT, c160.PIXEL_ASPECT
+
+
+def convert(img_rgb, palette_name="ntsc", dither_mode="floyd",
+            intensive=False, base_color=None):
+    # mono is carried by dithering -> needs error diffusion
+    if dither_mode not in DIFFUSION_DITHERS:
+        dither_mode = "floyd"
+    hue = 0 if base_color is None else (int(base_color) & 0x0F)
+    candidates = list(range(hue * 16, hue * 16 + 16))     # 16 lums of this hue
+    conv = c160.convert(img_rgb, palette_name, dither_mode, intensive,
+                        base_color=base_color, candidates=candidates, _mode="mono")
+    # report error in LUMINANCE space (a greyscale image must not be scored
+    # against the colour original, as the colour modes are)
+    plab = apal.palette_lab("ntsc").copy()
+    plab[:, 1:] = 0.0
+    img_l = c64pal.srgb_to_lab(img_rgb)
+    img_l[..., 1:] = 0.0
+    conv.error = perceptual_error(np.asarray(conv.index_image), img_l, plab)
+    conv.meta["base_color"] = base_color
+    return conv