如何在Python的OpenCV窗口标题中动态更新FPS

我正在用Python+OpenCV做视频相关开发，已经实现了在窗口左上角显示FPS，现在想把FPS移到窗口标题上。原代码如下：

import cv2
import datetime
import imutils

def GetCoord(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDOWN:
        print("X: {} | Y: {}".format(x, y))

winName = "My Project"
cv2.namedWindow(winName)
cv2.setMouseCallback(winName, GetCoord)

cap = cv2.VideoCapture(0)
fps_start_time = datetime.datetime.now()
fps = 0
total_frames = 0

while True:
    ret, frame = cap.read()
    frame = imutils.resize(frame, width=800)
    total_frames = total_frames + 1
    fps_end_time = datetime.datetime.now()
    time_diff = fps_end_time - fps_start_time
    if time_diff.seconds == 0:
        fps = 0.0
    else:
        fps = (total_frames / time_diff.seconds)
    fps_text = "FPS: {:.2f}".format(fps)
    cv2.putText(frame, fps_text, (5, 30), cv2.FONT_HERSHEY_COMPLEX_SMALL, 1, (0, 0, 255), 1)
    cv2.imshow(winName, frame)
    key = cv2.waitKey(1)
    if key == ord('q'):
        break

cv2.destroyAllWindows()

我尝试改成下面的代码，结果程序不断创建新窗口，运行异常：

cv2.imshow(winName + " FPS: {}".format(fps_text), frame)

问题原因 #

每次调用cv2.imshow()时传入新的窗口名称，OpenCV会判定为需要创建新窗口，循环执行时就会不断生成新窗口，导致程序异常。

正确实现方式 #

不要修改cv2.imshow()的窗口名，而是使用cv2.setWindowTitle()方法修改已创建窗口的标题，具体步骤：

1. 保留初始创建的窗口名winName，循环中继续用cv2.imshow(winName, frame)显示画面；
2. 计算出FPS后，用cv2.setWindowTitle()将窗口标题设置为原名称+FPS信息；
3. 若不需要在画面内显示FPS，可删除cv2.putText()代码行。

修改后的完整代码：

import cv2
import datetime
import imutils

def GetCoord(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDOWN:
        print("X: {} | Y: {}".format(x, y))

winName = "My Project"
cv2.namedWindow(winName)
cv2.setMouseCallback(winName, GetCoord)

cap = cv2.VideoCapture(0)
fps_start_time = datetime.datetime.now()
fps = 0
total_frames = 0

while True:
    ret, frame = cap.read()
    if not ret:
        break  # 防止读取帧失败导致报错
    frame = imutils.resize(frame, width=800)
    total_frames += 1
    fps_end_time = datetime.datetime.now()
    time_diff = fps_end_time - fps_start_time
    # 改用包含微秒的总秒数计算，避免前几秒秒数为0的问题
    total_seconds = time_diff.total_seconds()
    if total_seconds == 0:
        fps = 0.0
    else:
        fps = total_frames / total_seconds
    fps_text = "FPS: {:.2f}".format(fps)
    # 更新窗口标题
    cv2.setWindowTitle(winName, f"{winName} {fps_text}")
    # 不需要画面内显示FPS则删除此行
    # cv2.putText(frame, fps_text, (5, 30), cv2.FONT_HERSHEY_COMPLEX_SMALL, 1, (0, 0, 255), 1)
    cv2.imshow(winName, frame)
    key = cv2.waitKey(1)
    if key == ord('q'):
        break

cap.release()  # 释放摄像头资源
cv2.destroyAllWindows()

额外优化 #

• 原代码用time_diff.seconds计算FPS，前几秒可能因秒数为0导致FPS显示异常，改用total_seconds = time_diff.total_seconds()包含微秒，计算更准确；
• 添加cap.release()释放摄像头资源，避免程序退出后资源占用。

内容的提问来源于stack exchange，提问作者S Andrew