day3 直方图

1.绘制直方图

# coding=utf-8

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

img1 = cv2.imread('woman.JPEG',0)
cv2.imshow("woman",img1)

#matplotlib中绘制直方图函数  matplotlib.pyplot.hist()
plt.hist(img1.ravel(),256,[0,256])
       #img1.ravel() 将图像转化为数组
                    #BIN的数目，将256个值分成256份
                          #像素值范围
plt.show()

cv2.waitKey(0)
cv2.destroyAllWindows()

2.多通道直方图

# coding=utf-8

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

img = cv2.imread('woman.JPEG')
cv2.imshow("woman",img)

color = ('b','g','r')

# 对一个列表或数组既要遍历索引又要遍历元素时
# 使用内置 enumerrate 函数

for i,col in enumerate(color):
    histr = cv2.calcHist([img],[i],None,[256],[0,256])
                               #i：通道  None：掩模图像
    plt.plot(histr,color = col )
    plt.xlim([0,256])

plt.show()

cv2.waitKey(0)
cv2.destroyAllWindows()