使用 opencv 每 1 秒尝试保存一帧时出现问题

Question

我尝试运行下面的代码，它运行成功但图像没有保存在系统的任何地方。有谁知道问题出在哪里或解决方案？

import cv2
import time

# open the default camera
cap = cv2.VideoCapture(0)

# set the width and height of the frame
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)

# set the start time
start_time = time.time()

# loop through the frames
print("looping through frames")
while True:
    # capture a frame
    ret, frame = cap.read()

    t = time.localtime()
    current_time = time.strftime("%H:%M:%S", t)

    # define the output file name and format
    output_file = f'/Frame_{current_time}.jpg'
    output_format = 'JPEG'

    # check if the frame is captured successfully
    if not ret:
        break

    # calculate the elapsed time
    elapsed_time = time.time() - start_time

    # check if 1 second has passed
    if elapsed_time >= 1:
        print("1 second passed")
        # save the frame as an image file
        cv2.imwrite(f'/TestFrames/{output_file}', frame)
        print(output_file)
        print("image saved")

        # reset the start time
        start_time = time.time()
        print("time reset")

    # display the frame
    cv2.imshow('frame', frame)

    # check for the 'q' key to quit
    if cv2.waitKey(1) == ord('q'):
        break

# release the camera and close all windows
cap.release()
cv2.destroyAllWindows()

我尝试运行下面的代码，它运行成功但图像没有保存在系统的任何地方。

Answer 1

主要问题是图像文件名包含冒号（

:

）字符，冒号字符是无效字符（至少对于Windows）文件名。

为了测试，我们可以检查

cv2.imwrite

的返回状态（状态是

True

成功，

False

失败）：

is_ok = cv2.imwrite(f'/TestFrames/{output_file}', frame)
print(output_file)

if is_ok:
    print("image saved")
else:
    print("Failed saving the image")

---

假设我们使用的是 Windows：

我们可以将

:

字符替换为

_

例如：

output_file = f'Frame_{current_time}.jpg'
output_file = output_file.replace(":", "_")

---

下面的回答建议把冒号替换成一个看起来像冒号的unicode字符“꞉”，但是

cv2.imwrite

不支持unicode字符（至少在Windows中不支持）。

如果我们想使用 '

\ua789

' unicode 字符，我们可以使用

cv2.imencode

和二进制文件编写：

with open(f'/TestFrames/{output_file}', 'wb') as f:  # Open image file as binary file for writing
    cv2.imencode('.'+output_format, frame)[1].tofile(f)  # encode the image as JPEG, and write the encoded image to the file (use [1] because cv2.imencode returns a tuple).

---

使用 unicode 字符代替冒号的代码示例：

import cv2
import time

# open the default camera
cap = cv2.VideoCapture(0)

# set the width and height of the frame
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 480)

# set the start time
start_time = time.time()

# loop through the frames
print("looping through frames")
while True:
    # capture a frame
    ret, frame = cap.read()

    t = time.localtime()
    current_time = time.strftime("%H:%M:%S", t)

    # define the output file name and format
    output_file = f'Frame_{current_time}.jpg'
    output_file = output_file.replace(":", "\ua789")  # Replace colon character with a character that looks like colon
    #output_file = output_file.replace(":", "_")  # Replace colon character with a underscore character
    output_format = 'JPEG'

    # check if the frame is captured successfully
    if not ret:
        break

    # calculate the elapsed time
    elapsed_time = time.time() - start_time

    # check if 1 second has passed
    if elapsed_time >= 1:
        print("1 second passed")

        # save the frame as an image file
        #is_ok = cv2.imwrite(f'/TestFrames/{output_file}', frame)

        with open(f'/TestFrames/{output_file}', 'wb') as f:  # Open image file as binary file for writing
            cv2.imencode('.'+output_format, frame)[1].tofile(f)  # encode the image as JPEG, and write the encoded image to the file (use [1] because cv2.imencode returns a tuple).

        print(output_file)
        print("image saved")

        # reset the start time
        start_time = time.time()
        print("time reset")

    # display the frame
    cv2.imshow('frame', frame)

    # check for the 'q' key to quit
    if cv2.waitKey(1) == ord('q'):
        break

# release the camera and close all windows
cap.release()

cv2.destroyAllWindows()