Create Your Own Colormap

• Detailed reference document of the VCS colormap can be found at here.

• Let’s create your own VCS colormap.

• Download ipynb file

Tutorial written by Jiwoo Lee (Oct. 2017)

Colormap for example 4 provided by Karl Taylor

Contents

• Import modules

• Prepare a dummy array

• Create a colormap

• Alternative way of creating own colormaps

• Define name and colors for your own colormap

  • Example 1

  • Example 2

  • Example 3

  • Example 4

Import modules

(back to top)

import vcs
import MV2
from matplotlib.colors import LinearSegmentedColormap

Prepare a dummy array

(back to top) - Here I prepare a dummy 2D array (240 x 2), which is being used in this tutorial only for the visualization purpose.

a = []

num_levels = 240

for i in range(0,num_levels):
  a.append(i/float(num_levels))

for i in range(0,num_levels):
  a.append(i/float(num_levels))

a = MV2.array(a)
a = MV2.reshape(a, (-1,num_levels))

a.id = 'dummy'

v = vcs.init()

Create a colormap

(back to top) - List of VCS default colormaps can be shown using vcs.listelements('colormap')

vcs.listelements('colormap')

['AMIP',
 'NCAR',
 'bl_to_darkred',
 'bl_to_drkorang',
 'blends',
 'blue2darkorange',
 'blue2darkred',
 'blue2green',
 'blue2grey',
 'blue2orange',
 'blue2orange2red',
 'blue_to_grey',
 'blue_to_grn',
 'blue_to_orange',
 'blue_to_orgred',
 'brown2blue',
 'brown_to_blue',
 'categorical',
 'classic',
 'default',
 'green2magenta',
 'grn_to_magenta',
 'inferno',
 'lightblue2darkblue',
 'ltbl_to_drkbl',
 'magma',
 'plasma',
 'rainbow',
 'rainbow_no_grn',
 'rainbownogreen',
 'sequential',
 'viridis',
 'white2blue',
 'white2green',
 'white2magenta',
 'white2red',
 'white2yellow',
 'white_to_blue',
 'white_to_green',
 'white_to_magenta',
 'white_to_red',
 'white_to_yellow']

• You can create your own colormap by using `createcolormap <https://uvcdat.llnl.gov/docs/vcs/Canvas.html?highlight=createcolormap#vcs.Canvas.Canvas.createcolormap>`__

• Let’s make one named ‘my_cmap’. Now you will see that one is included in the list of available colormaps

• Note that ‘my_cmap’ colormap is copy of the default colormap at the begining

v.createcolormap('my_cmap')
vcs.listelements('colormap')

['AMIP',
 'NCAR',
 'bl_to_darkred',
 'bl_to_drkorang',
 'blends',
 'blue2darkorange',
 'blue2darkred',
 'blue2green',
 'blue2grey',
 'blue2orange',
 'blue2orange2red',
 'blue_to_grey',
 'blue_to_grn',
 'blue_to_orange',
 'blue_to_orgred',
 'brown2blue',
 'brown_to_blue',
 'categorical',
 'classic',
 'default',
 'green2magenta',
 'grn_to_magenta',
 'inferno',
 'lightblue2darkblue',
 'ltbl_to_drkbl',
 'magma',
 'my_cmap',
 'plasma',
 'rainbow',
 'rainbow_no_grn',
 'rainbownogreen',
 'sequential',
 'viridis',
 'white2blue',
 'white2green',
 'white2magenta',
 'white2red',
 'white2yellow',
 'white_to_blue',
 'white_to_green',
 'white_to_magenta',
 'white_to_red',
 'white_to_yellow']

• Set colormap for the canvas by using `setcolormap <https://uvcdat.llnl.gov/docs/vcs/Canvas.html?highlight=setcolormap#vcs.Canvas.Canvas.setcolormap>`__ of VCS

v.setcolormap('my_cmap')

• Let’s make the colormap palette as pure white first

• Note that ‘my_cmap’ colormap is copy of the default colormap at the beginning

for i in range(0,240):
    v.setcolorcell(i,100,100,100)

• Assign colors with index number to ‘my_cmap’ using `setcolormap <https://uvcdat.llnl.gov/docs/vcs/Canvas.html?highlight=setcolorcell#vcs.Canvas.Canvas.setcolorcell>`__ of VCS

• Below example colors are given from here

v.setcolorcell(0,0,0,0) # black
v.setcolorcell(1,50,50,50) # gray
v.setcolorcell(2,75,75,75) # silver
v.setcolorcell(3,100,100,100) # white
v.setcolorcell(4,50,0,0) # maroon
v.setcolorcell(5,100,0,0) # red
v.setcolorcell(6,50,50,0) # olive
v.setcolorcell(7,100,100,0) # yellow
v.setcolorcell(8,0,50,0) # green
v.setcolorcell(9,0,100,0) # lime
v.setcolorcell(10,0,50,50) # teal
v.setcolorcell(11,0,100,100) # aqua
v.setcolorcell(12,0,0,50) # navy
v.setcolorcell(13,0,0,100) # blue
v.setcolorcell(14,50,0,50) # purple
v.setcolorcell(15,100,0,100) # fuchsia

• Use box.color_1 and box.color_2 of boxfill to set starting and ending colors

box = v.createboxfill()
box.color_1 = 0
box.color_2 = 15
box.colormap = 'my_cmap'
v.plot(a,box)

Alternative way of creating own colormaps

(back to top)

• Alternative way of creating your own VCS colormap uses combined capability of UV-CDAT’s VCS and Matplotlib.

• Below simply written function receives name of colormap (cmap_name as string), and list of colors (colors as list of strings or tuples). User can define colors using either (1) named color of Matplotlib or (2) tuples of R, G, B numbers (0-1).

• `LinearSegmentedColormap <https://matplotlib.org/devdocs/api/_as_gen/matplotlib.colors.LinearSegmentedColormap.html>`__ of `matplotlib.colors <https://matplotlib.org/api/colors_api.html>`__, imported from the begining, stretchs given colors with smooth transition.

• `matplotlib2vcs <https://uvcdat.llnl.gov/docs/vcs/misc/colors.html>`__ of vcs.colors convert given Matplotlib colormap to VCS colormap.

def CreateOwnColormap(cmap_name, colors):

    # Create a Matplotlib colomap
    cm = LinearSegmentedColormap.from_list(cmap_name, colors, N=240)

    # Convert Matplotlib colormap to VCS one
    vcs_cmap = vcs.colors.matplotlib2vcs(cm, vcs_name=cmap_name)

    return vcs_cmap

Define name and colors for your own colormap

(back to top)

• For colors, use list of either (1) named color of Matplotlib or (2) tuples of R, G, B numbers (0-1)

Example 1

(back to top)

• Define colors by using named color of Matplotlib

# Define my own colormap (name and sequentially varying colors)
cmap_name = 'cmap1'
colors = ['white','red','orange',
          'yellow','green','blue','violet',
          'purple','black']
CreateOwnColormap(cmap_name, colors)

<vcs.colormap.Cp at 0x12183fa48>

• Visualize example 1

box = v.createboxfill()
box.color_1 = 0
box.color_2 = 239

box.colormap = 'cmap1'
v.plot(a,box)

Example 2

(back to top)

• Define colors by using list of tuples of R, G, B numbers (0-1)

cmap_name2 = 'cmap2'
colors2 = [(1,0,0),(1,1,1),(0,0,1)] # red, white, blue
CreateOwnColormap(cmap_name2, colors2)

<vcs.colormap.Cp at 0x11f0ea470>

• Visualize example 2

v.clear()
box.colormap = 'cmap2'
v.plot(a,box)

Example 3

(back to top)

• Similar to example 1 but with more complicated set up.

cmap_name3 = 'cmap3'
colors3 = ['white','lavender','royalblue','navy',
           'darkviolet','darkred','tomato','darkorange',
           'orange','yellow']
CreateOwnColormap(cmap_name3, colors3)

<vcs.colormap.Cp at 0x11f0ea368>

• Visualize example 3

v.clear()
box.colormap = 'cmap3'
v.plot(a,box)

Example 4

(back to top)

• Similar to example 2 but with more complicated set up.

cmap_name4 = 'cmap4'

colors4 = [(99,93,60),
           (99,80,40),
           (99,60,20),
           (99,40,11),
           (99,0,0),
           (51,0,0),
           (44,11,62),
           (0,40,99),
           (20,60,99),
           (40,80,99),
           (60,93,99),
           (80,99,99),
          ]

colors4 = MV2.divide(colors4,100.) # Convert range 0-100 to 0-1

CreateOwnColormap(cmap_name4, colors4)

<vcs.colormap.Cp at 0x11f086100>

v.clear()
box.colormap = 'cmap4'
v.plot(a,box)