Matplotlib : What is the function of cmap in imshow?

Question

I\'m trying to learn opencv using python and came across this code below:

import cv2
import numpy as np
from matplotlib import pyplot as plt

BLUE = [255,0,         


        

Answer 1

When img1 has shape (M,N,3) or (M,N,4), the values in img1 are interpreted as RGB or RGBA values. In this case the cmap is ignored. Per the help(plt.imshow) docstring:

cmap : ~matplotlib.colors.Colormap, optional, default: None

If None, default to rc image.cmap value. cmap is ignored when X has RGB(A) information

However, if img were an array of shape (M,N), then the cmap controls the colormap used to display the values.

---

import numpy as np
import matplotlib.pyplot as plt
import mpl_toolkits.axes_grid1 as axes_grid1
np.random.seed(1)

data = np.random.randn(10, 10)

fig = plt.figure()
grid = axes_grid1.AxesGrid(
    fig, 111, nrows_ncols=(1, 2), axes_pad = 0.5, cbar_location = "right",
    cbar_mode="each", cbar_size="15%", cbar_pad="5%",)

im0 = grid[0].imshow(data, cmap='gray', interpolation='nearest')
grid.cbar_axes[0].colorbar(im0)

im1 = grid[1].imshow(data, cmap='jet', interpolation='nearest')
grid.cbar_axes[1].colorbar(im1)
plt.savefig('/tmp/test.png', bbox_inches='tight', pad_inches=0.0, dpi=200,)