First public commit.

lenser/apple/convert/hgr_mono.py

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+"""Apple II HGR monochrome: 280x192, 1 bit/pixel, black & white.
+
+Universal across the Apple II+ and //e.  Tone is carried entirely by dithering.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ... import dither
+from ...convert.base import Conversion, perceptual_error
+from .. import palette as apal
+
+WIDTH, HEIGHT = 280, 192
+PIXEL_ASPECT = 1.0
+DATA_ADDR = 0x2000        # HGR page 1
+
+
+def convert(img_rgb, palette_name="mono", dither_mode="floyd",
+            intensive=False, base_color=None):
+    from ...palette import srgb_to_lab
+    plab = apal.mono_lab()                      # 2 entries: black, white
+    L = srgb_to_lab(img_rgb)[..., 0]
+    img_mono = np.zeros((HEIGHT, WIDTH, 3))
+    img_mono[..., 0] = L
+    plab_mono = np.zeros((2, 3))
+    plab_mono[:, 0] = plab[:, 0]
+
+    allowed = np.tile(np.array([0, 1]), (HEIGHT, WIDTH, 1))
+    idx = dither.quantize(img_mono, allowed, plab_mono, dither_mode).astype(np.uint8)
+
+    data = apal.pack_hgr_mono(idx)              # 8192-byte HGR buffer
+    preview = (apal.MONO.astype(np.uint8))[idx]
+
+    return Conversion(
+        mode="hgr_mono", width=WIDTH, height=HEIGHT, pixel_aspect=PIXEL_ASPECT,
+        index_image=idx.astype(np.uint16), data=data, data_addr=DATA_ADDR,
+        viewer="hgr", preview_rgb=preview,
+        error=perceptual_error(idx, img_mono, plab_mono),
+        meta={"palette": "mono", "dither": dither_mode},
+    )