Matplotlib: How to change colorbar gradient using user input

问题

I want to customize the colorbar(colormap) with specific value range. The color range should varies with the given parameter (Tup,Tmd,Tbt) where

Tup: User selected Upper value
Tmid: User selected Mid Point
Tbt:User selected bottom point

Mid color (lime) should range through user selected Tup and Tbt with Tmd as a mid-point.

I tried to generate custom colormap using below code snippet, but could not able to control its range using user provided values.

cmap = LinearSegmentedColormap.from_list("", ["blue","gray","lime","gray","red"])
cax = ax.pcolor(data,cmap=cmap,edgecolors='k',vmin=0,vmax=100)

How to control colormap values depending on user input?

回答1:

You can use a combination of LinearSegmentedColormap to create the colormap, and DiverginNorm to define the end- and center-points.

Demonstration (code is not optimized, but it shows the general idea):

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider
from matplotlib import colors

maxV = 100
minV = -100
centerV = -50
N=10
data = np.random.uniform(low=minV, high=maxV, size=(N,N))
cmap = colors.LinearSegmentedColormap.from_list('', ['blue','lime','red'])
norm = colors.DivergingNorm(vmin=minV, vcenter=centerV, vmax=maxV)


fig, (ax, axSlide1, axSlide2, axSlide3) = plt.subplots(4,1, gridspec_kw=dict(height_ratios=[100,5,5,5]))
im = ax.imshow(data, cmap=cmap, norm=norm)
cbar = fig.colorbar(im, ax=ax)


axcolor = 'lightgoldenrodyellow'
for sax in [axSlide1, axSlide2, axSlide3]:
    sax.set_facecolor(axcolor)

smin = Slider(axSlide1, 'min', minV, maxV, valinit=minV)
scenter = Slider(axSlide2, 'center', minV, maxV, valinit=centerV)
smax = Slider(axSlide3, 'max', minV, maxV, valinit=maxV)



def update(val):
    global cbar
    minV = smin.val
    maxV = smax.val
    centerV = scenter.val
    if minV>maxV:
        minV=maxV
        smin.set_val(minV)
    if maxV<minV:
        maxV=minV
        smax.set_val(maxV)
    if centerV<minV:
        centerV = minV
        scenter.set_val(centerV)
    if centerV>maxV:
        centerV = maxV
        scenter.set_val(centerV)

    #redraw with new normalization
    norm = colors.DivergingNorm(vmin=minV, vcenter=centerV, vmax=maxV)
    ax.cla()
    cbar.ax.cla()
    im = ax.imshow(data, cmap=cmap, norm=norm)
    cbar = fig.colorbar(im, cax=cbar.ax)
    fig.canvas.draw_idle()


smin.on_changed(update)
smax.on_changed(update)
scenter.on_changed(update)

plt.show()

来源：https://stackoverflow.com/questions/61220770/matplotlib-how-to-change-colorbar-gradient-using-user-input

标签

python

matplotlib

colormap