Why can't I plot image histogram's in python-OpenCV

Question

I have to get a image, apply Histogram equalization and plot the histogram of both images (original and modified). So I tried this code:

import cv2
import numpy as np
from skimage import io, img_as_float, img_as_ubyte
import matplotlib.pyplot as plt  
from matplotlib import pyplot as plt

gray = cv2.imread("folder\img1.jpg",0)


equ = cv2.equalizeHist(gray)

io.imshow(gray)
io.imshow(equ)

histr = cv2.calcHist([gray],[0],None,[256],[0,256])
  
plt.plot(histr)
plt.show()

But The plot returned is..:

How can I fix it?

You could just use Mathplotlib histograms. See w3schools.com/python/matplotlib_histograms.asp and google.com/… — fmw42
– fmw42, Commented Jun 25, 2021 at 21:59

Rotem · Accepted Answer · 2021-06-25 21:56:45Z

1

You are not creating a new figure, so the histogram is plotted on the last figure that displays the image.
You may create a new figure before plotting the histogram:

histr = cv2.calcHist(gray, [0], None, [256], (0,255))

plt.figure() # Create new figure for the histogram plot
plt.plot(histr)
plt.show()

answered Jun 25, 2021 at 21:56

Rotem

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