How to plot 3d rgb histogram of a colored image in python

Question

I want to plot a 3d histogram of a colored image but I can only plot R and G value.what am I doing wrong here? or is there an easier way to do so

import numpy as np
import matplotlib.image as mpimg
from matplotlib import pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

img = mpimg.imread('model/obj4__0.png')
pixels = img.shape[0]*img.shape[1]
channels = 3
data = np.reshape(img[:, :, :channels], (pixels, channels))

histo_rgb, _ = np.histogramdd(data, bins=256)
histo_rg = np.sum(histo_rgb, 2)
levels = np.arange(256)

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
for g in levels:
    ax.bar(levels, histo_rg[:, g], zs=g, zdir='y', color='r')
ax.set_xlabel('Red')
ax.set_ylabel('Green')
ax.set_zlabel('Number of pixels')
plt.show()

Answer 1

If I understand your question well, I have the same issue, and found this: https://www.bogotobogo.com/python/OpenCV_Python/python_opencv3_image_histogram_calcHist.php

Here is the code for your question:

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

img = cv2.imread('images/GoldenGateSunset.png', -1)
cv2.imshow('GoldenGate',img)

color = ('b','g','r')
for channel,col in enumerate(color):
    histr = cv2.calcHist([img],[channel],None,[256],[0,256])
    plt.plot(histr,color = col)
    plt.xlim([0,256])
plt.title('Histogram for color scale picture')
plt.show()

while True:
    k = cv2.waitKey(0) & 0xFF     
    if k == 27: break             # ESC key to exit 
cv2.destroyAllWindows()

Note that this use cv2 functions but you can convert it to works with Numpy. I will try to figure out with numpy and give you an update.