Python OpenCV 直方图_hist.flaten-优快云博客

本文介绍如何使用Python结合OpenCV库来计算并显示图像的直方图，包括灰度图和彩色图的直方图绘制方法，并展示了如何在图像上直接绘制直方图。

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参考网址
OpenCV Python教程（3、直方图的计算与显示）_sunny2038的专栏-优快云博客
 opencv+python 统计及绘制直方图 - 简书

# -*- coding: utf-8 -*-

'''
Python OpenCV 显示直方图
'''

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


#%% 使用plt绘制灰度图
img = cv2.imread('lena.jpg',0)
plt.figure()
#plt.hist(img.ravel(),256,[0,256]); # img.ravel() 不建议
plt.hist(img.flatten(), bins=np.arange(0,256,1), density=0, facecolor='b',edgecolor='b')
 

#%% 使用plt绘制彩色图
plt.figure()
img3 = cv2.imread('lena.jpg',1)
color = ('b','g','r')
for i,col in enumerate(color):
    histr = cv2.calcHist([img3],[i],None,[256],[0,256])
    plt.plot(histr,color = col)
    plt.xlim([0,256])
plt.show()

#%% 在图像上绘制
def calcAndDrawHist(image, color):  
    hist= cv2.calcHist([image], [0], None, [256], [0.0,255.0])  
    minVal, maxVal, minLoc, maxLoc = cv2.minMaxLoc(hist)  
    histImg = np.zeros([256,256,3], np.uint8)  
    hpt = int(0.9* 256);  
      
    for h in range(256):  
        intensity = int(hist[h]*hpt/maxVal)  
        cv2.line(histImg,(h,256), (h,256-intensity), color)  
          
    return histImg;

img3 = cv2.imread('lena.jpg',1)
b, g, r = cv2.split(img3)    
histImgB = calcAndDrawHist(b, [255, 0, 0])  
histImgG = calcAndDrawHist(g, [0, 255, 0])  
histImgR = calcAndDrawHist(r, [0, 0, 255])  
  
cv2.imshow("histImgB", histImgB)  
cv2.imshow("histImgG", histImgG)  
cv2.imshow("histImgR", histImgR)    
cv2.waitKey(0)  
cv2.destroyAllWindows()