Fix linear colormap function to use HSL, not HSV

packages/pidplots/pidplots/colors.py

@@ -50,12 +50,28 @@ def make_colormap(color_list, detectors=True):
     return cmap
 
 
+def _hsv_to_hsl(color):
+    H = color[0]
+    L = color[2] * (1 - 0.5 * color[1])
+    S = 0 if (L == 0 or L == 1) else (color[2] - L) / min(L, 1 - L)
+    return (H, S, L)
+
+
+def _hsl_to_hsv(color):
+    H = color[0]
+    V = color[2] + color[1] * min(color[2], 1 - color[2])
+    S = 0 if V == 0 else 2 * (1 - color[2] / V)
+    return (H, S, V)
+
+
 def make_linear_colormap(color, cmap_name="custom_cmap", low=0.3, high=0.9):
     from matplotlib.colors import to_rgba, rgb_to_hsv, hsv_to_rgb
 
     hsv = rgb_to_hsv(to_rgba(color, alpha=1)[:3])
-    lo = hsv_to_rgb((hsv[0], hsv[1], low))
-    hi = hsv_to_rgb((hsv[0], hsv[1], high))
+    hsl = _hsv_to_hsl(hsv)
+
+    lo = hsv_to_rgb(_hsl_to_hsv((hsl[0], hsl[1], low)))
+    hi = hsv_to_rgb(_hsl_to_hsv((hsl[0], hsl[1], high)))
 
     cdict = {
         "red": ((0.0, lo[0], lo[0]), (1.0, hi[0], hi[0])),