How to create histogram of binary image?

Question

I have binary image (only 2 color, black and white),

I want to create histogram of the image. I have tried with these code:

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

img = cv2.imread('bin_003.png')
color = ('b','g','r')
for i,col in enumerate(color):
    histr = cv2.calcHist([img],[i],None,[256],[0,256])
    plt.plot(histr,color = col)
    plt.xlim([0,256])
plt.show()

But the code shows instead of showing only 0 and 1 at the x axis.

White is (255,255,255) so I don't know why you're surprised. — Mark Ransom
– Mark Ransom, Commented Jun 7, 2018 at 16:13
Actually I'm not surprised, i mean, i want to make the axis become only "0" and "1". For example "0" for 0 and "1" for 255 @MarkRansom — Dian Arief R
– Dian Arief R, Commented Jun 7, 2018 at 16:31

ImportanceOfBeingErnest · Accepted Answer · 2018-06-07 16:55:22Z

4

Since you have a black and white image here, it should only have a single channel. You wouldn't need RGB channels. You may create a single histogram by using plt.hist.

from matplotlib import pyplot as plt

img = plt.imread('https://i.sstatic.net/y19dr.png')

plt.hist(img.flatten(), bins=[-.5,.5,1.5], ec="k")
plt.xticks((0,1))
plt.show()

answered Jun 7, 2018 at 16:55

ImportanceOfBeingErnest

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