[英]Convert matplotlib figure to numpy array of same shape
I have an 256x256 image and I want to be able to plot a regression line through the points. 我有一个256x256的图片,我希望能够通过这些点绘制一条回归线。 To do this I converted the image to a scatter plot and then tried to convert the scatter plot back to a numpy array. 为此,我将图像转换为散点图,然后尝试将散点图转换回numpy数组。 However, conversion back to a numpy array made the numpy array 480x640. 但是,转换回numpy数组会使numpy数组变为480x640。
Would anyone please be able to explain to me why the shape changes, mainly why it's no longer a square image, and if there's any conversion to fix it? 任何人都可以向我解释为什么形状发生变化,主要是为什么它不再是正方形图像,以及是否有任何固定方法可以修复?
imagetile = a[2]
x, y = np.where(imagetile>0)
imagetile.shape
Out: (256L, 256L) 出:(256L,256L)
from numpy import polyfit
from numpy import polyval
imagetile = a[2]
x, y = np.where(imagetile>0)
from numpy import polyfit
from numpy import polyval
p2 = polyfit(x, y, 2)
fig = plt.figure()
ax = fig.add_axes([0.,0.,1.,1.])
xp = np.linspace(0, 256, 256)
plt.scatter(x, y)
plt.xlim(0,256)
plt.ylim(0,256)
plt.plot(xp, polyval(p2, xp), "b-")
plt.show()
fig.canvas.draw()
X = np.array(fig.canvas.renderer._renderer)
X.shape
Out: (480L, 640L, 4L) 出:(480L,640L,4L)
def fig2data ( fig ):
"""
@brief Convert a Matplotlib figure to a 4D numpy array with RGBA channels and return it
@param fig a matplotlib figure
@return a numpy 3D array of RGBA values
"""
# draw the renderer
fig.canvas.draw ( )
# Get the RGBA buffer from the figure
w,h = fig.canvas.get_width_height()
buf = np.fromstring ( fig.canvas.tostring_argb(), dtype=np.uint8 )
buf.shape = ( w, h,4 )
# canvas.tostring_argb give pixmap in ARGB mode. Roll the ALPHA channel to have it in RGBA mode
buf = np.roll ( buf, 3, axis = 2 )
return buf
figure = matplotlib.pyplot.figure( )
plot = figure.add_subplot ( 111 )
x, y = np.where(imagetile>0)
p2 = polyfit(x, y, 2)
plt.scatter(x, y)
plt.xlim(0,256)
plt.ylim(0,256)
plt.plot(xp, polyval(p2, xp), "b-")
data = fig2data(figure)
data.shape
Out: (640L, 480L, 4L) 出:(640L,480L,4L)
Thank you 谢谢
If you call matplotlib.pyplot.figure without setting the argument figsize, it takes on a default shape (quote from the documentation): 如果您在未设置参数figsize的情况下调用matplotlib.pyplot.figure ,它将采用默认形状(文档中的引号):
figsize : (float, float), optional, default: None width, height in inches. figsize :(浮动,浮动),可选,默认设置:无宽度,以英寸为单位的高度。 If not provided, defaults to rcParams["figure.figsize"] = [6.4, 4.8]. 如果未提供,则默认为rcParams [“ figure.figsize”] = [6.4,4.8]。
So, you could set the shape by doing 因此,您可以通过以下方式设置形状
matplotlib.pyplot.figure(figsize=(2.56,2.56))
Not knowing what your data looks like, I think your approach is rather roundabout, so, I suggest something like this: 不知道您的数据是什么样子,我认为您的方法相当is回,所以,我建议如下所示:
import numpy as np
import matplotlib.pyplot as plt
# generating simulated polynomial data:
arr = np.zeros((256, 256))
par = [((a-128)**2, a) for a in range(256)]
par = [p for p in par if p[0]<255]
arr[zip(*par)] = 1
x, y = np.where(arr>0)
p2 = np.polyfit(y, x, 2)
xp = np.linspace(0,256,256)
plt.imshow(arr) # show the image, rather than the conversion to datapoints
p = np.poly1d(p2) # recommended in the documentation for np.polyfit
plt.plot(xp, p(xp))
plt.ylim(0,256)
plt.xlim(0,256)
plt.show()
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