访问Raspberry Pi上运行的Docker容器中的picamera时出错

Question

我正在Raspberry Pi 4上使用docker-compose运行Docker容器，并希望使用Python中的picamera模块访问PiHQCam。我尝试使用以下教程使其工作：https://www.losant.com/blog/how-to-access-the-raspberry-pi-camera-in-docker。但是，在尝试构建映像时，它给了我以下错误：

ValueError: This system does not appear to be a Raspberry Pi

然后我尝试了自己的解决方案（见下文），但遇到了以下错误：

picamera.exc.PiCameraMMALError: Failed to create MMAL component b'vc.camera_info': I/O error

以下是我的设置：

docker-compose.yml：

version: '3.8'

services: 
  camera:
    build: camera
    image: eye_camera     
    devices:
      - /dev/vchiq

Dockerfile：

FROM balenalib/rpi-raspbian:latest

RUN apt-get update && \
    apt-get upgrade && \
    apt-get install -y python3 \
      python3-pip

WORKDIR /app

COPY requirements.txt .
RUN pip3 install -r requirements.txt

COPY . .

RUN groupadd -r -g 888 app && \
    useradd -r -u 888 -g app -d /app app && \
    chown -R app:app /app && \
    usermod -a -G video app
USER app

CMD ["python3", "./main.py"]

main.py：

import picamera

def main():
    print("Hello World!")

    cam = picamera.PiCamera()
    img = picamera.array.PiRGBArray(cam)
    cam.capture(img)
    cam.close()

if __name__ == '__main__':
    main()

初始化相机时PiCameraMMALError会立即出现。这是完整的错误输出：

camera_1 | Hello World!
camera_1 | Traceback (most recent call last):
camera_1 |   File "main.py", line 19, in <module>
camera_1 |     main()
camera_1 |   File "main.py", line 12, in main
camera_1 |     cam = picamera.PiCamera()
camera_1 |   File "/usr/local/lib/python3.7/dist-packages/picamera/camera.py", line 367, in __init__
camera_1 |     with mo.MMALCameraInfo() as camera_info:
camera_1 |   File "/usr/local/lib/python3.7/dist-packages/picamera/mmalobj.py", line 2346, in __init__
camera_1 |     super(MMALCameraInfo, self).__init__()
camera_1 |   File "/usr/local/lib/python3.7/dist-packages/picamera/mmalobj.py", line 633, in __init__
camera_1 |     prefix="Failed to create MMAL component %s" % self.component_type)
camera_1 |   File "/usr/local/lib/python3.7/dist-packages/picamera/exc.py", line 184, in mmal_check
camera_1 |     raise PiCameraMMALError(status, prefix)
camera_1 | picamera.exc.PiCameraMMALError: Failed to create MMAL component b'vc.camera_info': I/O error
camera_1 | mmal: mmal_vc_shm_init: could not initialize vc shared memory service
camera_1 | mmal: mmal_vc_component_create: failed to initialise shm for 'vc.camera_info' (7:EIO)
camera_1 | mmal: mmal_component_create_core: could not create component 'vc.camera_info' (7)

这里有什么问题？谢谢你的帮助！我很乐意提供更多信息：）

Answer 1

出于一些完全无法理解的原因，你需要魔法咒语“READTHEDOCS=True”来避免这个问题！以下Dockerfile使用它在Raspberry Pi 4上运行良好，但如果没有它，Docker映像构建将失败，出现您看到的错误：

FROM arm32v7/python:latest

# Set in container
ENV TZ=Europe/London

# See https://github.com/waveform80/picamera/issues/578
ENV READTHEDOCS=True

COPY ./src /app    

WORKDIR /app

RUN pip install  upgrade pip setuptools wheel

RUN pip install picamera

VOLUME ["/data"]

CMD ["/usr/bin/python", "camera.py"]

我使用docker build命令构建了它：

docker build -t jrcamera:latest .

并使用docker run命令运行它：

docker run  privileged=true -v /opt/vc:/opt/vc  env LD_LIBRARY_PATH=/opt/vc/lib  device /dev/vchiq -it jrcamera:latest

它在src目录（复制到Docker图像中的/app）中使用以下python脚本camera.py运行了一次处理：

from time import sleep
from datetime import datetime
from picamera import PiCamera

camera = PiCamera()

camera.resolution = (1280, 720)

camera.annotate_text_size = 16  # Can be in range 6 to 160 inclusive, with default 32

MAX_ITER = 5

for iter_no in range(0,MAX_ITER):

    camera.start_preview()

    #  It is important to sleep for at least two seconds before capturing an image,
    #  because this gives the cameras sensor time to sense the light levels
    #
    sleep(3)

    # Annotate image with current datetime, to nearest millisecond
    #
    date_time = datetime.utcnow().strftime('%Y-%m-%d_%H-%M-%S.%f')[:-3]

    camera.annotate_text = date_time

    camera.capture("/data/image_{0:}.jpg".format(date_time))

    camera.stop_preview()

（现在我只需要想一想如何将我的图像大小从710兆字节大到可笑，但这是另一个问题。）