More stable HSL saturation calculation

facelessuser · Mar 21, 2021 · bc339af · bc339af
1 parent 2284c9d
commit bc339af
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Showing 3 changed files with 8 additions and 2 deletions.
diff --git a/coloraide/__meta__.py b/coloraide/__meta__.py
@@ -188,5 +188,5 @@ def parse_version(ver):
     return Version(major, minor, micro, release, pre, post, dev)
 
 
-__version_info__ = Version(0, 1, 0, "alpha", 11)
+__version_info__ = Version(0, 1, 0, "alpha", 12)
 __version__ = __version_info__._get_canonical()
diff --git a/coloraide/colors/hsl.py b/coloraide/colors/hsl.py
@@ -28,7 +28,7 @@ def srgb_to_hsl(rgb):
             h = (b - r) / c + 2.0
         else:
             h = (r - g) / c + 4.0
-        s = 0 if l == 0 or l == 1 else c / (1.0 - abs(2.0 * l - 1))
+        s = 0 if l == 0 or l == 1 else (mx - l) / min(l, 1 - l)
         h *= 60.0
 
     return HSL._constrain_hue(h), s * 100.0, l * 100.0

diff --git a/docs/src/markdown/about/changelog.md b/docs/src/markdown/about/changelog.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## 0.1.0a12
+
+- **FIX**: More stable saturation calculation for HSL to ensure divide by zero doesn't occur.
+  `2(V - L) / (1 - abs(2 * L - 1))` is likely to yield zero in the denominator when `L` is very small, while the
+  equivalent `(V - L) / min(L, 1 - L)` is not.
+
 ## 0.1.0a11
 
 - **FIX**: Ensure that when `hex`, `compress`, and `names` is enabled in `to_string` for `srgb` that colors will still