Re: [Matplotlib-users] Single color transparent colormap
On 2014/11/19, 1:03 PM, Benjamin Root wrote:
What you are seeing is the fact that the adjacent cells share the same
coordinates, so neighboring cells overlap by one pixel. This is only
visible when alpha != 1. This is a tricky issue to solve, but I could
have sworn we made some progress on that front by setting snap to
False somewhere. There have been past discussions about it, for sure...
I don't think we ever made any progress; it seems like a problem with
the renderer itself, agg in this case, and one that differs from one
renderer to another (e.g., if the plot is saved as pdf and then rendered
by different libraries). Try turning off antialiasing.
Eric
Ben Root
On Wed, Nov 19, 2014 at 12:57 PM, Loïc Estève loic.est...@inria.fr
mailto:loic.est...@inria.fr wrote:
Thanks for the suggestions, I have tried the easiest one for now,
namely pcolormesh, see attached plot. The alpha colormap look great
but I can't seem to figure out how to prevent the edges of the cells
from being visible. I tried using edgecolors='none' to no avail. I
guess retrospectively that is similar to the lines we see in the
colormap on the right.
The snippet I am using:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
import matplotlib
matplotlib.rcParams['figure.__facecolor'] = 'white'
cm_dict = {'red': ((0.0, 1.0, 1.0),
(1.0, 1.0, 1.0)),
'green': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'blue': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'alpha': ((0.0, 0.0, 0.0),
(1.0, 1.0, 1.0))
}
my_cm = LinearSegmentedColormap('my___cm', cm_dict)
vals = np.tile(np.linspace(-1, 1, 30), (20, 1))
fig = plt.figure()
ax = plt.pcolormesh(vals, cmap=my_cm)
plt.colorbar()
plt.show()
Cheers,
Loïc
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[Matplotlib-users] Single color transparent colormap
Dear all,
I am trying to create a colormap with a single color (red in the example below)
where the alpha varies from 0 to 1. It does look like I am getting some grayish
color near the low alpha values (around alpha = 0.2). Is that expected somehow?
The plot I get is here:
https://cloud.githubusercontent.com/assets/1680079/5084457/7d2d3790-6f06-11e4-9021-5b9e77e6a9c4.png
I am using matplotlib 1.4.2.
Here is a snippet which reproduces the issue.
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
import matplotlib
matplotlib.rcParams['figure.facecolor'] = 'white'
cm_dict = {'red': ((0.0, 1.0, 1.0),
(1.0, 1.0, 1.0)),
'green': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'blue': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'alpha': ((0.0, 0.0, 0.0),
(1.0, 1.0, 1.0))
}
my_cm = LinearSegmentedColormap('my_cm', cm_dict)
vals = np.tile(np.linspace(-1, 1, 30), (20, 1))
fig = plt.figure()
ax = plt.imshow(vals, cmap=my_cm)
plt.colorbar()
plt.show()
Cheers,
Loïc
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Re: [Matplotlib-users] Single color transparent colormap
Confirmed. I am going to wager that this might be related to some of the
work that is being done right now in master to improve alpha handling,
particularly with images. Notice that the colormap looks fine for the
colorbar because it isn't using imshow() under the hood.
First, if you could try using the development version of matplotlib, we
have updated the AGG codebase. Maybe that might make an improvement off the
bat. If not, you can follow this PR that is a work in progress that might
be relevant: https://github.com/matplotlib/matplotlib/pull/3783
I hope this helps!
Ben Root
On Wed, Nov 19, 2014 at 9:46 AM, Loic Esteve loic.est...@inria.fr wrote:
Dear all,
I am trying to create a colormap with a single color (red in the example
below) where the alpha varies from 0 to 1. It does look like I am getting
some grayish color near the low alpha values (around alpha = 0.2). Is that
expected somehow?
The plot I get is here:
https://cloud.githubusercontent.com/assets/1680079/5084457/7d2d3790-6f06-11e4-9021-5b9e77e6a9c4.png
I am using matplotlib 1.4.2.
Here is a snippet which reproduces the issue.
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
import matplotlib
matplotlib.rcParams['figure.facecolor'] = 'white'
cm_dict = {'red': ((0.0, 1.0, 1.0),
(1.0, 1.0, 1.0)),
'green': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'blue': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'alpha': ((0.0, 0.0, 0.0),
(1.0, 1.0, 1.0))
}
my_cm = LinearSegmentedColormap('my_cm', cm_dict)
vals = np.tile(np.linspace(-1, 1, 30), (20, 1))
fig = plt.figure()
ax = plt.imshow(vals, cmap=my_cm)
plt.colorbar()
plt.show()
Cheers,
Loïc
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Re: [Matplotlib-users] Single color transparent colormap
On Wed, Nov 19, 2014 at 10:20:23AM -0500, Benjamin Root wrote: Notice that the colormap looks fine for the colorbar because it isn't using imshow() under the hood. As a short-term workaround (I work with Loic, and I it would help me a lot if his problem was solved with a hack), can we leverage the mechanism used to plot the colorbar ourselves? That doesn't preclude fixing the problem in master, of course. Cheers, Gaël -- Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751iu=/4140/ostg.clktrk ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] Single color transparent colormap
Did you try pcolormesh? Cheers, Jody On Nov 19, 2014, at 7:23 AM, Gael Varoquaux gael.varoqu...@normalesup.org wrote: On Wed, Nov 19, 2014 at 10:20:23AM -0500, Benjamin Root wrote: Notice that the colormap looks fine for the colorbar because it isn't using imshow() under the hood. As a short-term workaround (I work with Loic, and I it would help me a lot if his problem was solved with a hack), can we leverage the mechanism used to plot the colorbar ourselves? That doesn't preclude fixing the problem in master, of course. Cheers, Gaël -- Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751iu=/4140/ostg.clktrk ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users -- Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751iu=/4140/ostg.clktrk ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] Single color transparent colormap
Thanks for the suggestions, I have tried the easiest one for now, namely
pcolormesh, see attached plot. The alpha colormap look great but I can't
seem to figure out how to prevent the edges of the cells from being
visible. I tried using edgecolors='none' to no avail. I guess
retrospectively that is similar to the lines we see in the colormap on
the right.
The snippet I am using:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
import matplotlib
matplotlib.rcParams['figure.facecolor'] = 'white'
cm_dict = {'red': ((0.0, 1.0, 1.0),
(1.0, 1.0, 1.0)),
'green': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'blue': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'alpha': ((0.0, 0.0, 0.0),
(1.0, 1.0, 1.0))
}
my_cm = LinearSegmentedColormap('my_cm', cm_dict)
vals = np.tile(np.linspace(-1, 1, 30), (20, 1))
fig = plt.figure()
ax = plt.pcolormesh(vals, cmap=my_cm)
plt.colorbar()
plt.show()
Cheers,
Loïc
--
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Re: [Matplotlib-users] Single color transparent colormap
What you are seeing is the fact that the adjacent cells share the same
coordinates, so neighboring cells overlap by one pixel. This is only
visible when alpha != 1. This is a tricky issue to solve, but I could have
sworn we made some progress on that front by setting snap to False
somewhere. There have been past discussions about it, for sure...
Ben Root
On Wed, Nov 19, 2014 at 12:57 PM, Loïc Estève loic.est...@inria.fr wrote:
Thanks for the suggestions, I have tried the easiest one for now, namely
pcolormesh, see attached plot. The alpha colormap look great but I can't
seem to figure out how to prevent the edges of the cells from being
visible. I tried using edgecolors='none' to no avail. I guess
retrospectively that is similar to the lines we see in the colormap on the
right.
The snippet I am using:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
import matplotlib
matplotlib.rcParams['figure.facecolor'] = 'white'
cm_dict = {'red': ((0.0, 1.0, 1.0),
(1.0, 1.0, 1.0)),
'green': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'blue': ((0.0, 0.0, 0.0),
(1.0, 0.0, 0.0)),
'alpha': ((0.0, 0.0, 0.0),
(1.0, 1.0, 1.0))
}
my_cm = LinearSegmentedColormap('my_cm', cm_dict)
vals = np.tile(np.linspace(-1, 1, 30), (20, 1))
fig = plt.figure()
ax = plt.pcolormesh(vals, cmap=my_cm)
plt.colorbar()
plt.show()
Cheers,
Loïc
--
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