I took a stab at it, how does this look?
I also took the liberty of adding alpha to LinearSegmentedColormap and
updated its docstring changing two somewhat ambiguous uses of the word
'entry' with 'key' and 'value'.
tested with
In [1]: import matplotlib; import numpy as np
In [2]: my_rgba_array= np.array( [[ 1., 1., 1., 0.65],
[ 1., 0., 0., 0.79]])
In [3]: myColormap = matplotlib.colors.ListedColormap(my_rgba_array)
In [4]: myColormap.__call__(.1)
Out[4]: (1.0, 1.0, 1.0, 0.65000000000000002)
In [5]: myColormap.__call__(.9)
Out[5]: (1.0, 0.0, 0.0, 0.790000000000000
In [6]: my_rgba_array= np.array( [ [ 1. , 1. , 1. ],
[ 1. , 0. , 0. ]])
In [7]: myColormap = matplotlib.colors.ListedColormap(my_rgba_array)
In [8]: myColormap.__call__(.1)
Out[8]: (1.0, 1.0, 1.0, 1.0)
In [9]: myColormap.__call__(.9)
Out[9]: (1.0, 0.0, 0.0, 1.0)
cheers,
Paul Ivanov
John Hunter, on 2008-11-21 05:52, wrote:
> On Fri, Nov 21, 2008 at 2:45 AM, Simon Kammerer <[EMAIL PROTECTED]> wrote:
>
>> After looking at the source of matplotlib.colors, it seems to me that
>> different alpha values are something Colormap is not designed for.
>
> Yes, it looks like the colormap only holds the RGB channels, but it
> also looks fairly straightforward to patch the code to support the
> fourth channel. Is this something you'd like to tackle?
>
> JDH
>
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Index: lib/matplotlib/colors.py
===================================================================
--- lib/matplotlib/colors.py (revision 6431)
+++ lib/matplotlib/colors.py (working copy)
@@ -452,7 +452,7 @@
self._isinit = False
- def __call__(self, X, alpha=1.0, bytes=False):
+ def __call__(self, X, alpha=None, bytes=False):
"""
*X* is either a scalar or an array (of any dimension).
If scalar, a tuple of rgba values is returned, otherwise
@@ -466,9 +466,10 @@
"""
if not self._isinit: self._init()
- alpha = min(alpha, 1.0) # alpha must be between 0 and 1
- alpha = max(alpha, 0.0)
- self._lut[:-3, -1] = alpha
+ if alpha:
+ alpha = min(alpha, 1.0) # alpha must be between 0 and 1
+ alpha = max(alpha, 0.0)
+ self._lut[:-3, -1] = alpha
mask_bad = None
if not cbook.iterable(X):
vtype = 'scalar'
@@ -558,9 +559,10 @@
def __init__(self, name, segmentdata, N=256):
"""Create color map from linear mapping segments
- segmentdata argument is a dictionary with a red, green and blue
- entries. Each entry should be a list of *x*, *y0*, *y1* tuples,
- forming rows in a table.
+ segmentdata argument is a dictionary with red, green and blue
+ keys. An optional alpha key is also supported. Each value
+ should be a list of *x*, *y0*, *y1* tuples, forming rows in a
+ table.
Example: suppose you want red to increase from 0 to 1 over
the bottom half, green to do the same over the middle half,
@@ -606,6 +608,8 @@
self._lut[:-3, 0] = makeMappingArray(self.N, self._segmentdata['red'])
self._lut[:-3, 1] = makeMappingArray(self.N, self._segmentdata['green'])
self._lut[:-3, 2] = makeMappingArray(self.N, self._segmentdata['blue'])
+ if self._segmentdata.has_key('alpha'):
+ self._lut[:-3, 3] = makeMappingArray(self.N, self._segmentdata['blue'])
self._isinit = True
self._set_extremes()
@@ -664,11 +668,10 @@
def _init(self):
- rgb = np.array([colorConverter.to_rgb(c)
+ rgba = np.array([colorConverter.to_rgba(c)
for c in self.colors], np.float)
self._lut = np.zeros((self.N + 3, 4), np.float)
- self._lut[:-3, :-1] = rgb
- self._lut[:-3, -1] = 1
+ self._lut[:-3] = rgba
self._isinit = True
self._set_extremes()
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