First public commit.

lenser/atari/convert/gr8.py

@@ -0,0 +1,40 @@
+"""Atari GR.8 (ANTIC mode F): 320x192 hi-res, two tones of one hue.
+
+Highest spatial resolution; carries tone by dithering between background and a
+foreground luminance.  ``base_color`` picks the hue (None = greyscale).
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ...convert.base import Conversion, perceptual_error
+from .. import palette as apal
+from . import _common
+
+WIDTH, HEIGHT = 320, 192
+PIXEL_ASPECT = 1.0
+
+
+def convert(img_rgb, palette_name="ntsc", dither_mode="floyd",
+            intensive=False, base_color=None):
+    hue = 0 if base_color is None else (int(base_color) & 0x0F)
+    bg_reg = (hue << 4) | 0x00            # darkest of the hue
+    fg_reg = (hue << 4) | 0x0E            # brightest of the hue
+    plab = apal.palette_lab(palette_name)
+    prgb = apal.get_palette(palette_name).astype(np.uint8)
+
+    img_mono, plab_mono = _common.luminance_lab(img_rgb, plab)
+    idx = _common.quantize_global(img_mono, plab_mono, [bg_reg, fg_reg], dither_mode)
+    val = (idx == fg_reg).astype(np.uint8)
+
+    data = _common.split_screen(_common.pack_1bpp(val)) + bytes([bg_reg, fg_reg])
+    preview = prgb[idx]                    # already 320 wide
+
+    return Conversion(
+        mode="gr8", width=WIDTH, height=HEIGHT, pixel_aspect=PIXEL_ASPECT,
+        index_image=idx.astype(np.uint16), data=data, data_addr=_common.DATA_ADDR,
+        viewer="gr8", preview_rgb=preview,
+        error=perceptual_error(idx, img_mono, plab_mono),
+        meta={"palette": palette_name, "dither": dither_mode, "hue": hue},
+    )