Add alpha to an existing matplotlib colormap

by

I’m not quite sure if this qualifies within “not knowing the inner structure of the colormap”, but perhaps something like this would work to add a linear alpha to an existing colormap?

import numpy as np
import matplotlib.pylab as pl
from matplotlib.colors import ListedColormap

# Random data
data1 = np.random.random((4,4))

# Choose colormap
cmap = pl.cm.RdBu

# Get the colormap colors
my_cmap = cmap(np.arange(cmap.N))

# Set alpha
my_cmap[:,-1] = np.linspace(0, 1, cmap.N)

# Create new colormap
my_cmap = ListedColormap(my_cmap)

pl.figure()
pl.subplot(121)
pl.pcolormesh(data1, cmap=pl.cm.RdBu)
pl.colorbar()

pl.subplot(122)
pl.pcolormesh(data1, cmap=my_cmap)
pl.colorbar()

enter image description here

More Related Contents:

  1. Set Colorbar Range in matplotlib
  2. Defining the midpoint of a colormap in matplotlib
  3. Matplotlib Plot Lines with Colors Through Colormap
  4. How to decode color mapping in matplotlib’s Colormap?
  5. Change the facecolor of boxplot in pandas
  6. How to pick a new color for each plotted line within a figure
  7. Matplotlib scatterplot; color as a function of a third variable
  8. Pandas – Plotting a stacked Bar Chart
  9. matplotlib does not show my drawings although I call pyplot.show()
  10. Seaborn Barplot – Displaying Values
  11. How to make a 4d plot with matplotlib using arbitrary data
  12. How to give a pandas/matplotlib bar graph custom colors
  13. Matplotlib: Finding out xlim and ylim after zoom
  14. List of all available matplotlib backends
  15. How to remove frame from matplotlib (pyplot.figure vs matplotlib.figure ) (frameon=False Problematic in matplotlib)
  16. How to hide in IPython notebook
  17. How to export plots from matplotlib with transparent background?
  18. Putting arrowheads on vectors in matplotlib’s 3d plot
  19. Animate points with labels with matplotlib
  20. Matplotlib – logarithmic scale, but require non-logarithmic labels
  21. Python: find contour lines from matplotlib.pyplot.contour()
  22. Remove line through marker in matplotlib legend
  23. ImportError: Cannot load backend ‘TkAgg’ which requires the ‘tk’ interactive framework, as ‘headless’ is currently running
  24. Python making combined bar and line plot with secondary y-axis
  25. Cancelling the offset on an axis [duplicate]
  26. Unable to “import matplotlib.pyplot as plt” in virtualenv
  27. pylab.hist(data, normed=1). Normalization seems to work incorrect
  28. Move spines in matplotlib 3d plot?
  29. Setting Different error bar colors in bar plot in matplotlib
  30. Matplotlib – Wrong overlapping when plotting two 3D surfaces on the same axes

Leave a Comment