How to plot 3d graphics with the values of each pixel of the image?

Question

I convert a picture's colors to LAB as follows:

import cv2
imbgr=cv2.imread('photo.jpg')
imlab=cv2.cvtColor(imbgr,cv2.COLOR_BGR2LAB)
cv2.imwrite('lab.jpg',imlab)

return the pixels with imlab [x, y], how to plot the graph with these values?

Answer 1

Here are a few examples of how to show images and graph image data as 3-d data.

The first and second figures show the original BGR image and its individual channels as BGR, and then as LAB.

The third and fourth figures show a contour map and a surface plot using the first channels of the LAB image as 3-D data.

Aside: Notice that imshow() needs an RGB image. And, if desired, the contour plot can be made square, using the aspect keyword, aspect='equal' or, set_aspect().

import cv2
import numpy as np

import matplotlib.image as mpimg

import matplotlib.pyplot as plt

# for the surface map
from mpl_toolkits.mplot3d import Axes3D

imbgr = cv2.imread('Mona_Lisa.jpg')

imrgb = cv2.cvtColor(imbgr, cv2.COLOR_BGR2RGB)

imlab=cv2.cvtColor(imbgr,cv2.COLOR_BGR2LAB)

# Show the original image and individual color channels
plt.figure(0)
plt.subplot(2,2,1)

plt.imshow( imrgb )

plt.subplot(2,2,2)
plt.imshow(imbgr[:,:,0], cmap='Blues')

plt.subplot(2,2,3)
plt.imshow(imbgr[:,:,1], cmap='Greens')

plt.subplot(2,2,4)
plt.imshow(imbgr[:,:,2], cmap='Reds')

plt.show()

# show the LAB space iamge
plt.figure(1)
plt.subplot(2,2,1)

plt.imshow( imrgb )

plt.subplot(2,2,2)
plt.imshow(imlab[:,:,0], cmap='Greys')

plt.subplot(2,2,3)
plt.imshow(imbgr[:,:,1], cmap='cool')

plt.subplot(2,2,4)
plt.imshow(imbgr[:,:,2], cmap='cool')

plt.show()

# contour map
plt.figure(2)

y = range( imlab.shape[0] )
x = range( imlab.shape[1] ) 
X, Y = np.meshgrid(x, y)

plt.contour( X, Y, imlab[:,:,0], 50 )

plt.show()

# surface map
plt.figure(3)

ax = plt.axes(projection='3d')

y = range( imlab.shape[0] )
x = range( imlab.shape[1] ) 
X, Y = np.meshgrid(x, y)

ax.plot_surface( X, Y, imlab[:,:,0] )

plt.show()

And here are the images generated by the code, as listed.

Figure(0) - original image and individual color channels

Figure(1) - LAB image and individual channels

Figure(2) - Contour graph of first LAB channel

Figure(3) - surface plot of first LAB channel