Set Colorbar Range in matplotlib

Question

I have the following code   import matplotlib pyplot as plt  cdict        red         0 0  0 25   25    0 02   59   59    1   1   1        green       0 0  0 0  0 0    0 02   45   45    1    97   97       blue        0 0  1 0  1 0    0 02   75   75    1   0 45  0 45      cm   m colors LinearSegmentedColormap  my colormap   cdict  1024   plt clf   plt pcolor X  Y  v  cmap cm  plt loglog   plt xlabel  X Axis   plt ylabel  Y Axis    plt colorbar   plt show     So this produces a graph of the values  v  on the axes X vs Y  using the specified colormap  The X and Y axes are perfect  but the colormap spreads between the min and max of v  I would like to force the colormap to range between 0 and 1   I thought of using   plt axis        To set the ranges of the axes  but this only takes arguments for the min and max of X and Y  not the colormap   Edit   For clarity  let s say I have one graph whose values range  0     0 3   and another graph whose values  0 2     0 8    In both graphs  I will want the range of the colorbar to be  0     1   In both graphs  I want this range of colour to be identical using the full range of cdict above  so 0 25 in both graphs will be the same colour   In the first graph  all colours between 0 3 and 1 0 won t feature in the graph  but will in the colourbar key at the side  In the other  all colours between 0 and 0 2  and between 0 8 and 1 will not feature in the graph  but will in the colourbar at the side

User · Answer

Not sure if this is the most elegant solution (this is what I used), but you could scale your data to the range between 0 to 1 and then modify the colorbar:

import matplotlib as mpl
...
ax, _ = mpl.colorbar.make_axes(plt.gca(), shrink=0.5)
cbar = mpl.colorbar.ColorbarBase(ax, cmap=cm,
                       norm=mpl.colors.Normalize(vmin=-0.5, vmax=1.5))
cbar.set_clim(-2.0, 2.0)

With the two different limits you can control the range and legend of the colorbar. In this example only the range between -0.5 to 1.5 is show in the bar, while the colormap covers -2 to 2 (so this could be your data range, which you record before the scaling).

So instead of scaling the colormap you scale your data and fit the colorbar to that.

User · Answer

Use the CLIM function  equivalent to CAXIS function in MATLAB    plt pcolor X  Y  v  cmap cm  plt clim -4 4     identical to caxis  -4 4   in MATLAB plt show

User · Answer

Using figure environment and  set clim   Could be easier and safer this alternative if you have multiple plots  import matplotlib as m import matplotlib pyplot as plt import numpy as np  cdict        red         0 0  0 25   25    0 02   59   59    1   1   1        green       0 0  0 0  0 0    0 02   45   45    1    97   97       blue        0 0  1 0  1 0    0 02   75   75    1   0 45  0 45      cm   m colors LinearSegmentedColormap  my colormap   cdict  1024   x   np arange 0  10   1  y   np arange 0  10   1  X  Y   np meshgrid x y   data   2   np sin X    np sin 3 Y    data1   np clip data 0 6  data2   np clip data -6 0  vmin   np min np array  data data1 data2    vmax   np max np array  data data1 data2     fig   plt figure   ax   fig add subplot 131  mesh   ax pcolormesh data  cmap   cm  mesh set clim vmin vmax  ax1   fig add subplot 132  mesh1   ax1 pcolormesh data1  cmap   cm  mesh1 set clim vmin vmax  ax2   fig add subplot 133  mesh2   ax2 pcolormesh data2  cmap   cm  mesh2 set clim vmin vmax    Visualizing colorbar part -start fig colorbar mesh ax ax  fig colorbar mesh1 ax ax1  fig colorbar mesh2 ax ax2  fig tight layout     Visualizing colorbar part -end  plt show     A single colorbar The best alternative is then to use a single color bar for the entire plot  There are different ways to do that  this tutorial is very useful for understanding the best option  I prefer this solution that you can simply copy and paste instead of the previous visualizing colorbar part of the code  fig subplots adjust bottom 0 1  top 0 9  left 0 1  right 0 8                      wspace 0 4  hspace 0 1  cb ax   fig add axes  0 83  0 1  0 02  0 8   cbar   fig colorbar mesh  cax cb ax    P S  I would suggest using pcolormesh instead of pcolor because it is faster  more infos here

User · Answer

Using vmin and vmax forces the range for the colors   Here s an example     import matplotlib as m import matplotlib pyplot as plt import numpy as np  cdict        red         0 0  0 25   25    0 02   59   59    1   1   1        green       0 0  0 0  0 0    0 02   45   45    1    97   97       blue        0 0  1 0  1 0    0 02   75   75    1   0 45  0 45      cm   m colors LinearSegmentedColormap  my colormap   cdict  1024   x   np arange 0  10   1  y   np arange 0  10   1  X  Y   np meshgrid x y   data   2   np sin X    np sin 3 Y     def do plot n  f  title        plt clf       plt subplot 1  3  n      plt pcolor X  Y  f data   cmap cm  vmin -4  vmax 4      plt title title      plt colorbar    plt figure   do plot 1  lambda x x   all   do plot 2  lambda x np clip x  -4  0     lt 0   do plot 3  lambda x np clip x  0  4     gt 0   plt show

[python] Set Colorbar Range in matplotlib

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