Histograms are a great way to visualize individual color components



In [2]:

    
import cv2
import numpy as np

# We need to import matplotlib to create our histogram plots
from matplotlib import pyplot as plt

image = cv2.imread('images/input.jpg')

histogram = cv2.calcHist([image], [0], None, [256], [0, 256])

# We plot a histogram, ravel() flatens our image array 
plt.hist(image.ravel(), 256, [0, 256]); plt.show()

# Viewing Separate Color Channels
color = ('b', 'g', 'r')

# We now separate the colors and plot each in the Histogram
for i, col in enumerate(color):
    histogram2 = cv2.calcHist([image], [i], None, [256], [0, 256])
    plt.plot(histogram2, color = col)
    plt.xlim([0,256])
    
plt.show()

cv2.calcHist(images, channels, mask, histSize, ranges[, hist[, accumulate]])

images : it is the source image of type uint8 or float32. it should be given in square brackets, ie, "[img]".
channels : it is also given in square brackets. It is the index of channel for which we calculate histogram. For example, if input is grayscale image, its value is [0]. For color image, you can pass [0], [1] or [2] to calculate histogram of blue, green or red channel respectively.
mask : mask image. To find histogram of full image, it is given as "None". But if you want to find histogram of particular region of image, you have to create a mask image for that and give it as mask. (I will show an example later.)
histSize : this represents our BIN count. Need to be given in square brackets. For full scale, we pass [256].
ranges : this is our RANGE. Normally, it is [0,256].



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In [4]:

    
import cv2
import numpy as np

# We need to import matplotlib to create our histogram plots
from matplotlib import pyplot as plt

image = cv2.imread('images/tobago.jpg')

histogram = cv2.calcHist([image], [0], None, [256], [0, 256])

# We plot a histogram, ravel() flatens our image array 
plt.hist(image.ravel(), 256, [0, 256]); plt.show()

# Viewing Separate Color Channels
color = ('b', 'g', 'r')

# We now separate the colors and plot each in the Histogram
for i, col in enumerate(color):
    histogram2 = cv2.calcHist([image], [i], None, [256], [0, 256])
    plt.plot(histogram2, color = col)
    plt.xlim([0,256])
    
plt.show()



In [5]:

    
image = cv2.imread('images/tobago.jpg')
cv2.imshow("Tobago", image) 

cv2.waitKey(0)
cv2.destroyAllWindows()



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