import cv2

input_filepath = 'Lenna.png'
output_filepath = ['R.txt', 'G.txt', 'B.txt']
img = cv2.imread(input_filepath)
imgRGB = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
# imgHSV = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
# imgLAB = cv2.cvtColor(img, cv2.COLOR_BGR2LAB)
for k in range(3):
    fd = open(output_filepath[k], 'w')
    for i in imgRGB[:, :, k]:
        fd.write(' '.join(['{:3}'.format(j) for j in i]) + '\n')
    fd.close()

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

input_filepath = 'Lenna.png'
img = cv2.imread(input_filepath)
# RGB
imgRGB = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
hist = [cv2.calcHist([imgRGB], [k], None, [256], [0, 256]) for k in range(3)]
x = np.arange(256) + 0.5
plt.subplot(221), plt.imshow(imgRGB)
plt.subplot(222), plt.bar(x, hist[0], color = 'r', edgecolor = 'r')
plt.subplot(223), plt.bar(x, hist[1], color = 'g', edgecolor = 'g')
plt.subplot(224), plt.bar(x, hist[2], color = 'b', edgecolor = 'b')
plt.show()
# HSV
imgHSV = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
hist = [cv2.calcHist([imgHSV], [0], None, [50], [0, 180]), \
    cv2.calcHist([imgHSV], [1], None, [50], [0, 256])]
x = np.arange(50) + 0.5
plt.subplot(211), plt.bar(x, hist[0])
plt.subplot(212), plt.bar(x, hist[1])
plt.show()

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

input_filepath = ['1.jpg', '2.jpg']
comp_method = [cv2.cv.CV_COMP_CORREL, cv2.cv.CV_COMP_INTERSECT, \
        cv2.cv.CV_COMP_CHISQR, cv2.cv.CV_COMP_BHATTACHARYYA]
# BGR
img = [cv2.imread(i) for i in input_filepath]
hist = [cv2.calcHist([i], [k], None, [256], [0, 256]) for k in range(3) for i in img]
for i in hist
    for j in i:
        cv2.normalize(j, j)
hist = [np.mean(i, 0) for i in hist]
for method in comp_method:
    d = cv2.compareHist(hist[0], hist[1], method)
    print(d)
# HSV
imgHSV = [cv2.cvtColor(i, cv2.COLOR_BGR2HSV) for i in img]
hist = [cv2.calcHist([i], [0, 1], None, [50, 50], [0, 180, 0, 256]) \
    for i in imgHSV]
for i in hist_set:
    cv2.normalize(i, i)
for method in comp_method:
    d = cv2.compareHist(hist[0], hist[1], method)
    print(d)