Convert cmap values to RGB for PIL.Image-CodePudding

I want to use PIL.Image to save a figure and I want to use matplotlib cmaps to map the data to a color. I have tried the following:

import matplotlib
matplotlib.use('TkAgg')
import matplotlib as mpl
import matplotlib.pyplot as plt
from matplotlib import cm
import numpy as np
from PIL import Image

M, N = 255, 255
data = np.arange(M*N).reshape((M, N))

cmap_name = 'autumn_r'
cmap_name = cmap_name
cmap = plt.get_cmap(cmap_name)
norm = mpl.colors.Normalize()
scalarMap = cm.ScalarMappable(norm=norm, cmap=cmap)

plt.imshow(data, cmap=cmap)
plt.show()

colors = scalarMap.to_rgba(data)

image = Image.fromarray((colors[:, :, :3]*256).astype(np.uint8))
image.show()

Which plots this in matplotlib:

However, it plots this in the Image:

How can I get PIL.Image to show the same colors as matplotlib?

If its possible to also add the alpha channel, that will be useful

CodePudding user response：

You need to give PIL the same normalisation and cmap you give matplotlib, so it can do the same mapping from 2D array -> normalised -> mapped to cmap.

I rewrote your sample code to be a bit simpler:

import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np
from matplotlib import cm
from PIL import Image

M, N = 255, 255
data = np.arange(M*N).reshape((M, N))
cmap = cm.autumn_r
plt.imshow(data, cmap=cmap)

norm = mpl.colors.Normalize()

Then your answer is:

Image.fromarray(np.uint8(cmap(norm(data))*255)).show()

(Found the solution here, might be a dupe.)