OpenCV Python灰度视频转RGB视频报错求助：VideoWriter参数错误

问题描述 #

需要将灰度格式的视频转换为彩色格式，参考了Stack Overflow上的RGB转灰度问题及OpenCV官方cv::VideoWriter文档后，编写了如下Python代码：

import cv2
import matplotlib.pyplot as plt
source =cv2.VideoCapture("test_video.mp4")
frame_width = int(source.get(3))
frame_height = int(source.get(4))
size = (frame_width, frame_height,3)
result = cv2.VideoWriter('color_version.avi',
                         cv2.VideoWriter_fourcc(*'MJPG'),
                         10, size, True)
# running the loop
while True:
    # extracting the frames
    ret, img = source.read()
    # converting to color format
    colored = cv2.cvtColor(img, cv2.COLOR_GRAY2RGB)
    # write to gray-scale
    result.write(colored)
    # displaying the video
    cv2.imshow("Live", colored)
    # exiting the loop
    key = cv2.waitKey(1)
    if key == ord("q"):
        break
# closing the window
cv2.destroyAllWindows()
source.release()

运行后出现如下错误：

cv2.error: OpenCV(4.5.5) :-1: error: (-5:Bad argument) in function 'VideoWriter'
> Overload resolution failed:
>  - Can't parse 'frameSize'. Expected sequence length 2, got 3
>  - Argument 'fps' can not be treated as a double
>  - Can't parse 'frameSize'. Expected sequence length 2, got 3
>  - VideoWriter() missing required argument 'params' (pos 6)

已设置isColor=true，但仍报错，询问代码问题所在。

错误原因及修正方案 #

1. VideoWriter的frameSize参数格式错误 #

OpenCV Python版的VideoWriter中，frameSize仅需传入二维元组(width, height)，不需要包含通道数（第三个维度）。你设置的size = (frame_width, frame_height,3)是三维结构，直接触发了错误提示里的"Expected sequence length 2, got 3"。isColor=True仅用于告知框架写入的是彩色帧，通道数由实际写入的帧自动适配，无需在frameSize中声明。

2. 缺少帧读取成功的判断 #

循环中未判断ret是否为True，当视频读取到末尾时，img会变为None，此时调用cv2.cvtColor会引发新的报错。

3. 其他优化点 #

• 移除未使用的matplotlib.pyplot导入，减少冗余；
• 将fps参数显式写成10.0（浮点数），避免部分OpenCV版本的类型匹配问题；
• 调整资源释放顺序，先释放VideoWriter和VideoCapture，再销毁窗口，更符合规范。

修正后的代码 #

import cv2

source = cv2.VideoCapture("test_video.mp4")
frame_width = int(source.get(3))
frame_height = int(source.get(4))
# 修正frameSize为二维元组
size = (frame_width, frame_height)
result = cv2.VideoWriter('color_version.avi',
                         cv2.VideoWriter_fourcc(*'MJPG'),
                         10.0,  # 显式使用浮点数fps
                         size, 
                         True)

while True:
    ret, img = source.read()
    # 判断帧读取是否成功，失败则退出循环
    if not ret:
        break
    # 将灰度帧转换为RGB彩色帧
    colored = cv2.cvtColor(img, cv2.COLOR_GRAY2RGB)
    result.write(colored)
    cv2.imshow("Live", colored)
    # 按下q键退出
    if cv2.waitKey(1) == ord("q"):
        break

# 按顺序释放资源
result.release()
source.release()
cv2.destroyAllWindows()

内容的提问来源于stack exchange，提问作者AI researcher