使用实时摄像机预览更新matplotlib中的帧 [英] update frame in matplotlib with live camera preview

问题描述

我是Python和Matplotlib的新手.我的计算机已连接到两个USB摄像机，我打算使用matplotlib中的subplot(1,2,1)和subplot(1,2,2)来按时间序列绘制两个摄像机的帧.当我用代码执行此操作时，要么只绘制一帧，要么在绘制区域出现黑屏.

I am new to both Python and Matplotlib. My computer is connected to two usb cameras, and I intend to use the subplot(1,2,1) and subplot(1,2,2) in matplotlib to plot the frames from the two camera in time series. When I do this with my code, I either get only one frame plotted or get a black screen in the plotting area.

我的代码如下所示

#import
import cv2
import matplotlib.pyplot as plt

#Initiate the two cameras
cap1 = cv2.VideoCapture(0)
cap2 = cv2.VideoCapture(1)

#Capture the frames from camera 1 and 2 and display them over time using matplotlib

while True:
    #grab frame from camera 1 and 2
    ret1,frame1 = cap1.read()
    ret2,frame2 = cap2.read()

    plt.subplot(1,2,1), plt.imshow(cv2.cvtColor(frame1,cv2.COLOR_BGR2RGB))
    plt.subplot(1,2,2), plt.imshow(cv2.cvtColor(frame2,cv2.COLOR_BGR2RGB))

    #draw the plot
    plt.show(False)
    #Result is black screen. If plt.show() is called, I see the frames but then it freezes.

推荐答案

交互模式

在matplotlib中更新图的一种方法是使用交互模式(plt.ion()). 然后，您不应为捕获的每个帧重新创建新的子图，而应使用图像创建一次绘图，然后再进行更新.

Interactive mode

One way of updating a plot in matplotlib is to use interactive mode (plt.ion()). You should then not recreate new subplots for each frame you capture, but create your plot with images once and update it afterwards.

import cv2
import matplotlib.pyplot as plt

def grab_frame(cap):
    ret,frame = cap.read()
    return cv2.cvtColor(frame,cv2.COLOR_BGR2RGB)

#Initiate the two cameras
cap1 = cv2.VideoCapture(0)
cap2 = cv2.VideoCapture(1)

#create two subplots
ax1 = plt.subplot(1,2,1)
ax2 = plt.subplot(1,2,2)

#create two image plots
im1 = ax1.imshow(grab_frame(cap1))
im2 = ax2.imshow(grab_frame(cap2))

plt.ion()

while True:
    im1.set_data(grab_frame(cap1))
    im2.set_data(grab_frame(cap2))
    plt.pause(0.2)

plt.ioff() # due to infinite loop, this gets never called.
plt.show()

FuncAnimation

当然还有另一个选择是使用Matplotlib内置的FuncAnimation，它是专门为动画绘制动画而设计的.

FuncAnimation

Another option is of course to use matplotlib's built in FuncAnimation which is especially designed to animate plots.

import cv2
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation

def grab_frame(cap):
    ret,frame = cap.read()
    return cv2.cvtColor(frame,cv2.COLOR_BGR2RGB)

#Initiate the two cameras
cap1 = cv2.VideoCapture(0)
cap2 = cv2.VideoCapture(1)

#create two subplots
ax1 = plt.subplot(1,2,1)
ax2 = plt.subplot(1,2,2)

#create two image plots
im1 = ax1.imshow(grab_frame(cap1))
im2 = ax2.imshow(grab_frame(cap2))

def update(i):
    im1.set_data(grab_frame(cap1))
    im2.set_data(grab_frame(cap2))

ani = FuncAnimation(plt.gcf(), update, interval=200)
plt.show()

为了在按键事件时关闭窗口，您可以像这样添加回调

In order to close the window on a key press event, you may add a callback, like so

#... other code
ani = FuncAnimation(plt.gcf(), update, interval=200)

def close(event):
    if event.key == 'q':
        plt.close(event.canvas.figure)

cid = plt.gcf().canvas.mpl_connect("key_press_event", close)

plt.show()

# code that should be executed after window is closed.

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