Adds access to inverted colormaps with _i appendix

- updates plots.py so that example plots are unchanged by additions
- adds documentation for inverted cmaps

Author: andrew-s28

Diff for: cmocean/cm.py

@@ -60,5 +60,24 @@ def _register_cmap(cmap, *, name):
     reg_map_r = colors.ListedColormap(rgb_with_alpha[::-1,:], N=rgb.shape[0])
     _register_cmap(reg_map_r, name=f'cmo.{cmapname}_r')
 
+    # Load inverted cmaps
+    rgb_i = np.loadtxt(os.path.join(datadir, 'inverted', cmapname + '_i-rgb.txt'))
+    cmap_d[cmapname + '_i'] = tools.cmap(rgb_i, N=256)
+    cmap_d[cmapname + '_i'].name = cmapname + '_i'
+    cmap_d[cmapname + '_r_i'] = tools.cmap(rgb_i[::-1, :], N=256)
+    cmap_d[cmapname + '_r_i'].name = cmapname + '_r_i'
+    rgb_with_alpha = np.zeros((rgb_i.shape[0],4))
+    rgb_with_alpha[:,:3] = rgb_i
+    rgb_with_alpha[:,3]  = 1.  #set alpha channel to 1
+
+    # Register inverted cmaps
+    reg_map_i = colors.ListedColormap(rgb_with_alpha, N=rgb_i.shape[0])
+    _register_cmap(reg_map_i, name=f'cmo.{cmapname}_i')
+    reg_map_r_i = colors.ListedColormap(rgb_with_alpha[::-1,:], N=rgb_i.shape[0])
+    _register_cmap(reg_map_r_i, name=f'cmo.{cmapname}_r_i')
+
+    # order shouldn't matter
+    cmap_d[cmapname + '_i_r'] = cmap_d[cmapname + '_r_i']
+
 # make colormaps available to call
 locals().update(cmap_d)

Diff for: cmocean/plots.py

@@ -25,7 +25,7 @@ def plot_lightness(saveplot=False):
     fig = plt.figure(figsize=(16, 5))
     ax = fig.add_subplot(111)
     fig.subplots_adjust(left=0.03, right=0.97)
-    ax.set_xlim(-0.1, len(cm.cmap_d)/2. + 0.1)
+    ax.set_xlim(-0.1, len(cm.cmap_d)/5. + 0.1)
     ax.set_ylim(0, 100)
     ax.set_xlabel('Lightness for each colormap', fontsize=14)
 
@@ -75,12 +75,12 @@ def plot_gallery(saveplot=False):
     gradient = np.vstack((gradient, gradient))
     x = np.linspace(0.0, 1.0, 256)
 
-    fig, axes = plt.subplots(nrows=int(len(cm.cmap_d)/2), ncols=1, figsize=(6, 12))
+    fig, axes = plt.subplots(nrows=int(len(cm.cmap_d)/5), ncols=1, figsize=(6, 12))
     fig.subplots_adjust(top=0.99, bottom=0.01, left=0.2, right=0.99, wspace=0.05)
 
     for ax, cmapname in zip(axes, cm.cmapnames):
 
-        if '_r' in cmapname:  # skip reversed versions for plot
+        if '_r' in cmapname or '_i' in cmapname:  # skip reversed versions for plot
             continue
 
         cmap = cm.cmap_d[cmapname]  # get the colormap instance

Diff for: cmocean/rgb/inverted/algae_i-rgb.txt

@@ -133,6 +133,22 @@ Reversed versions of all colormaps are available by appending "_r" to the colorm
    cmocean.plots.test(cmocean.cm.gray_r, ax=ax)
    fig.tight_layout()
 
+Inverted lightness versions of all colormaps are available by appending "_i" to the colormap name. This is particularly useful for diverging colormaps used on light backgrounds:
+
+.. plot::
+   :include-source:
+
+   import cmocean
+   import matplotlib.pyplot as plt
+
+   fig = plt.figure(figsize=(8, 3))
+   ax = fig.add_subplot(1, 2, 1)
+   cmocean.plots.test(cmocean.cm.balance, ax=ax)
+   ax = fig.add_subplot(1, 2, 2)
+   cmocean.plots.test(cmocean.cm.balance_i, ax=ax)
+   fig.tight_layout()
+
+Reversed and inverted lightness versions of all colormaps are available by appending "_r_i" or "_i_r" to the colormap name, e.g., ``cmocean.cm.balance_i_r``.
 
 You can lighten a colormap using an alpha value below 1 with the `cmocean.tools.lighten()` function so that you can overlay contours and other lines that are more easily visible: