wallpaper: better variant detection

src/caelestia/utils/colourfulness.py

@@ -0,0 +1,42 @@
+import math
+
+from PIL import Image
+
+
+def mean(values: list[float]) -> float:
+    return sum(values) / len(values) if values else 0
+
+
+def stddev(values: list[float], mean_val: float) -> float:
+    return math.sqrt(sum((x - mean_val) ** 2 for x in values) / len(values)) if values else 0
+
+
+def calc_colourfulness(image: Image) -> float:
+    width, height = image.size
+    pixels = list(image.getdata())  # List of (R, G, B) tuples
+
+    rg_diffs = []
+    yb_diffs = []
+
+    for r, g, b in pixels:
+        rg = abs(r - g)
+        yb = abs(0.5 * (r + g) - b)
+        rg_diffs.append(rg)
+        yb_diffs.append(yb)
+
+    mean_rg = mean(rg_diffs)
+    mean_yb = mean(yb_diffs)
+    std_rg = stddev(rg_diffs, mean_rg)
+    std_yb = stddev(yb_diffs, mean_yb)
+
+    return math.sqrt(std_rg**2 + std_yb**2) + 0.3 * math.sqrt(mean_rg**2 + mean_yb**2)
+
+
+def get_variant(image: Image) -> str:
+    colourfulness = calc_colourfulness(image)
+
+    if colourfulness < 10:
+        return "neutral"
+    if colourfulness < 20:
+        return "content"
+    return "tonalspot"

src/caelestia/utils/wallpaper.py

@@ -80,14 +80,16 @@ def get_smart_opts(wall: Path, cache: Path) -> str:
     except (IOError, json.JSONDecodeError):
         pass
 
+    from caelestia.utils.colourfulness import get_variant
+
+    opts = {}
+
     with Image.open(get_thumb(wall, cache)) as img:
+        opts["variant"] = get_variant(img)
+
         img.thumbnail((1, 1), Image.LANCZOS)
         hct = Hct.from_int(argb_from_rgb(*img.getpixel((0, 0))))
-
-        opts = {
-            "mode": "light" if hct.tone > 60 else "dark",
-            "variant": "neutral" if hct.chroma < 20 else "tonalspot",
-        }
+        opts["mode"] = "light" if hct.tone > 60 else "dark"
 
     opts_cache.parent.mkdir(parents=True, exist_ok=True)
     with opts_cache.open("w") as f: