I found that in scatter plots the alpha values given by individual
entries in the color list are ignored. Here an example that shows
different combinations of color and alpha arguments:
x = [1,2,3]
y = array([1,1,1])
c = [[1,0,0, 0.0],
[1,0,0, 0.5],
[1,0,0, 1.0]]
scatter(x, y, s = 200, c = 'r')
scatter(x, y + 1, s = 200, c = c)
scatter(x, y + 2, s = 200, c = c, alpha = 0.5)
scatter(x, y + 3, s = 200, c = 'g', alpha = 0.5)
Looking at the source in axes.py/scatter I found that replacing the
default value for the alpha keyword argument in the function header of
scatter from alpha=1.0 to alpha=None fixes this problem. Additionally, I
had to replace
collection.set_alpha(alpha)
by
if alpha is not None:
collection.set_alpha(alpha)
See also the attached diff file.
Gregor
Index: axes.py
===================================================================
--- axes.py (revision 6590)
+++ axes.py (working copy)
@@ -4873,7 +4872,7 @@
medians=medians, fliers=fliers)
def scatter(self, x, y, s=20, c='b', marker='o', cmap=None, norm=None,
- vmin=None, vmax=None, alpha=1.0, linewidths=None,
+ vmin=None, vmax=None, alpha=None, linewidths=None,
faceted=True, verts=None,
**kwargs):
"""
@@ -5136,7 +5135,8 @@
transOffset = self.transData,
)
collection.set_transform(mtransforms.IdentityTransform())
- collection.set_alpha(alpha)
+ if alpha is not None:
+ collection.set_alpha(alpha)
collection.update(kwargs)
if colors is None:
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