是否可以在matplotlib中获得曲线下的颜色渐变? [英] Is it possible to get color gradients under curve in matplotlib?
问题描述
I happened to see a beautiful graph on this page which is shown below:
是否可以在matplotlib中获得这样的颜色渐变?
Is it possible to get such color gradients in matplotlib?
推荐答案
以前,也有一些类似问题的答案(例如 https://stackoverflow.com/a/22081678/325565 ),但他们建议使用次优的方法.
There have been a handful of previous answers to similar questions (e.g. https://stackoverflow.com/a/22081678/325565), but they recommend a sub-optimal approach.
大多数先前的答案建议在pcolormesh
填充上绘制白色多边形.这不理想,原因有两个:
Most of the previous answers recommend plotting a white polygon over a pcolormesh
fill. This is less than ideal for two reasons:
- 轴的背景不能透明,因为上面有一个填充的多边形
-
pcolormesh
绘制速度很慢,并且插值不平滑.
- The background of the axes can't be transparent, as there's a filled polygon overlying it
pcolormesh
is fairly slow to draw and isn't smoothly interpolated.
需要更多的工作,但是有一种方法可以更快地绘制并提供更好的视觉效果:设置使用imshow
绘制的图像的剪切路径.
It's a touch more work, but there's a method that draws much faster and gives a better visual result: Set the clip path of an image plotted with imshow
.
例如:
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.colors as mcolors
from matplotlib.patches import Polygon
np.random.seed(1977)
def main():
for _ in range(5):
gradient_fill(*generate_data(100))
plt.show()
def generate_data(num):
x = np.linspace(0, 100, num)
y = np.random.normal(0, 1, num).cumsum()
return x, y
def gradient_fill(x, y, fill_color=None, ax=None, **kwargs):
"""
Plot a line with a linear alpha gradient filled beneath it.
Parameters
----------
x, y : array-like
The data values of the line.
fill_color : a matplotlib color specifier (string, tuple) or None
The color for the fill. If None, the color of the line will be used.
ax : a matplotlib Axes instance
The axes to plot on. If None, the current pyplot axes will be used.
Additional arguments are passed on to matplotlib's ``plot`` function.
Returns
-------
line : a Line2D instance
The line plotted.
im : an AxesImage instance
The transparent gradient clipped to just the area beneath the curve.
"""
if ax is None:
ax = plt.gca()
line, = ax.plot(x, y, **kwargs)
if fill_color is None:
fill_color = line.get_color()
zorder = line.get_zorder()
alpha = line.get_alpha()
alpha = 1.0 if alpha is None else alpha
z = np.empty((100, 1, 4), dtype=float)
rgb = mcolors.colorConverter.to_rgb(fill_color)
z[:,:,:3] = rgb
z[:,:,-1] = np.linspace(0, alpha, 100)[:,None]
xmin, xmax, ymin, ymax = x.min(), x.max(), y.min(), y.max()
im = ax.imshow(z, aspect='auto', extent=[xmin, xmax, ymin, ymax],
origin='lower', zorder=zorder)
xy = np.column_stack([x, y])
xy = np.vstack([[xmin, ymin], xy, [xmax, ymin], [xmin, ymin]])
clip_path = Polygon(xy, facecolor='none', edgecolor='none', closed=True)
ax.add_patch(clip_path)
im.set_clip_path(clip_path)
ax.autoscale(True)
return line, im
main()
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