First public commit.

lenser/coco/convert/pmode3.py

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+"""CoCo PMODE 3: 128x192, 4 colours from one MC6847 colour set.
+
+128 wide on a 4:3 screen -> 2:1 pixels (like C64 multicolor).  The 4 colours are
+fixed per CSS set (green/yellow/blue/red or buff/cyan/magenta/orange); we dither
+to whichever set reproduces the image with lower error and tell the viewer which.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ... import dither
+from ...convert.base import Conversion, perceptual_error
+from ...palette import srgb_to_lab
+from .. import palette as cpal
+
+WIDTH, HEIGHT = 128, 192
+PIXEL_ASPECT = 2.0
+
+
+def convert(img_rgb, palette_name="mc6847", dither_mode="floyd",
+            intensive=False, base_color=None):
+    img_lab = srgb_to_lab(img_rgb)
+    allowed = np.tile(np.array([0, 1, 2, 3]), (HEIGHT, WIDTH, 1))
+
+    best = None
+    for vdg, rgb in cpal.PMODE3_SETS.items():
+        plab = srgb_to_lab(rgb)
+        idx = dither.quantize(img_lab, allowed, plab, dither_mode).astype(np.uint8)
+        err = perceptual_error(idx, img_lab, plab)
+        if best is None or err < best[0]:
+            best = (err, vdg, rgb, plab, idx)
+
+    err, vdg, rgb, plab, idx = best
+    data = cpal.pack_pmode3(idx)                 # 6144-byte video buffer
+    preview = rgb.astype(np.uint8)[idx]
+
+    return Conversion(
+        mode="pmode3", width=WIDTH, height=HEIGHT, pixel_aspect=PIXEL_ASPECT,
+        index_image=idx.astype(np.uint16), data=data, data_addr=0,
+        viewer="pmode3", preview_rgb=preview,
+        error=err,
+        meta={"palette": "mc6847", "dither": dither_mode, "vdg": vdg},
+    )