Python+Matplotlib动态绘制直方图时旧水平参考线清除问题求助

问题根源 #

你原有方案的核心问题是：每次调用plt.hlines都会在画布上新增独立的线条对象，所有线条是叠加渲染而非覆盖替换，白色线条仅能覆盖同坐标的部分像素，无法彻底移除旧的线条对象，多次叠加后自然会出现颜色混杂、旧线残留的问题。

优化方案 #

提前初始化两条参考线对象，后续仅动态更新它们的Y轴位置即可，无需反复绘制新线也不需要手动擦除旧线，修改后的完整代码如下：

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

video = cv2.VideoCapture('output.avi') 

if (video.isOpened()== False):  
  print("Error opening video  file") 

max_history = 0
max_current = 0

x = np.linspace(0, 255, 256)
y = np.linspace(0.1, 100000, 256)
plt.ion()

# FPS变量
prev_frame_time = 0
new_frame_time = 0

# plt.subplots()函数返回包含画布和轴对象的元组
figure, ax = plt.subplots(1, 1, figsize=(10, 8))
line_hist, = ax.plot(x, y)
# 新增：提前初始化两条参考线
line_current_max, = ax.plot([0,255], [0,0], c='r', label='当前最大值')
line_history_max, = ax.plot([0,255], [0,0], c='g', label='上一次最大值')
ax.set_yscale('log')

while(video.isOpened()): 
    ret, image = video.read()
    if ret == True:
        
        gris = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
        smaller_image = cv2.resize(gris,(640,480))
        
        # 计算FPS
        font = cv2.FONT_HERSHEY_SIMPLEX # 字体
        new_frame_time = time.time()
        fps = 1/(new_frame_time - prev_frame_time)
        prev_frame_time = new_frame_time
        fps = int(fps)
        fps = str(fps)
        cv2.putText(smaller_image, fps, (7, 70), font, 3, (100, 255, 0), 3, cv2.LINE_AA)
        
        cv2.imshow('Image', smaller_image)
        
        histogram = cv2.calcHist([smaller_image], [0], None, [256], [0, 256])
        line_hist.set_ydata(histogram)
        
        max_new = np.amax(histogram[150:256])
        if max_new > max_current :
            # 更新历史最大值线位置
            line_history_max.set_ydata([max_current, max_current])
            # 更新当前最大值线位置
            line_current_max.set_ydata([max_new, max_new])
            # 刷新最大值存储变量
            max_history = max_current
            max_current = max_new
        
        figure.canvas.draw()
        figure.canvas.flush_events()
        time.sleep(0.001)
        
        if cv2.waitKey(25) & 0xFF == ord('q'): 
            break
    else :
        break    
plt.ioff()
video.release() 
cv2.destroyAllWindows()
plt.close('all')

内容的提问来源于stack exchange，提问作者lapasq