Mix dark colors with white, bright colors with black

Author: mgeier

sfs/plot2d.py

@@ -8,32 +8,37 @@
 from . import util as _util
 
 
-def _register_cmap_clip(name, original_name, col_alpha_u, col_apha_o):
+def _apply_alpha(rgba, alpha):
+    """Mix dark colors with white, bright colors with black."""
+    from colorsys import rgb_to_hls
+    r, g, b, a = rgba
+    _, l, _ = rgb_to_hls(r, g, b)
+    if l > 0.5:
+        return [alpha * c for c in [r, g, b]] + [a]
+    else:
+        return [alpha * c + 1 - alpha for c in [r, g, b]] + [a]
+
+
+def _register_cmap_clip(name, original_name, alpha):
     """Create a color map with "over" and "under" values."""
     cmap = _plt.get_cmap(original_name)
-    cmap = cmap.with_extremes(
-        under=cmap.get_under() * col_alpha_u,
-        over=cmap.get_over() * col_apha_o)
+    over = _apply_alpha(cmap.get_over(), alpha)
+    under = _apply_alpha(cmap.get_under(), alpha)
+    cmap = cmap.with_extremes(under=under, over=over)
     cmap.name = name
     _plt.colormaps.register(cmap=cmap)
 
 
-_register_cmap_clip('cividis_clip', 'cividis',
-                    [1, 1, 1, 0.6],[1, 1, 1, 0.1])
-_register_cmap_clip('cividis_r_clip', 'cividis_r',
-                    [1, 1, 1, 0.1], [1, 1, 1, 0.6])
-_register_cmap_clip('viridis_clip', 'viridis',
-                    [1, 1, 1, 0.6], [1, 1, 1, 0.1])
-_register_cmap_clip('viridis_r_clip', 'viridis_r',
-                    [1, 1, 1, 0.1], [1, 1, 1, 0.6])
+_register_cmap_clip('cividis_clip', 'cividis', 0.8)
+_register_cmap_clip('cividis_r_clip', 'cividis_r', 0.8)
+_register_cmap_clip('viridis_clip', 'viridis', 0.8)
+_register_cmap_clip('viridis_r_clip', 'viridis_r', 0.8)
 
 # The 'coolwarm' colormap is based on the paper
 # "Diverging Color Maps for Scientific Visualization" by Kenneth Moreland
 # https://www.kennethmoreland.com/color-maps/ColorMapsExpanded.pdf
-_register_cmap_clip('coolwarm_clip', 'coolwarm',
-                    [1, 1, 1, 0.5], [1, 1, 1, 0.5])
-_register_cmap_clip('coolwarm_r_clip', 'coolwarm_r',
-                    [1, 1, 1, 0.5], [1, 1, 1, 0.5])
+_register_cmap_clip('coolwarm_clip', 'coolwarm', 0.65)
+_register_cmap_clip('coolwarm_r_clip', 'coolwarm_r', 0.65)
 
 
 def _register_cmap_transparent(name, color):