OpenCV 无法访问 Python 中的网络摄像头

Question

Python 3.6.1, opencv-python 4.1.1, Windows 10.

Code:

import numpy as np 
from cv2 import cv2  
cap = cv2.VideoCapture(0)
while True:
    ret, frame = cap.read()
    cv2.imshow('frame', frame)

The webcam frame pops up but is blank, do I need to grant openCv access to my webcam somehow? The webcam is built into my laptop. Laptop is plugged into a docking station.

Build Information output below:

General configuration for OpenCV 4.1.1 =====================================
  Version control:               4.1.1

  Platform:
    Timestamp:                   2019-09-02T16:39:13Z
    Host:                        Windows 6.3.9600 AMD64
    CMake:                       3.15.1
    CMake generator:             Visual Studio 14 2015 Win64
    CMake build tool:            C:/Program Files (x86)/MSBuild/14.0/bin/MSBuild.exe
    MSVC:                        1900
  CPU/HW features:
    Baseline:                    SSE SSE2 SSE3
      requested:                 SSE3
    Dispatched code generation:  SSE4_1 SSE4_2 FP16 AVX AVX2
      requested:                 SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
      SSE4_1 (13 files):         + SSSE3 SSE4_1
      SSE4_2 (1 files):          + SSSE3 SSE4_1 POPCNT SSE4_2
      FP16 (0 files):            + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
      AVX (4 files):             + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
      AVX2 (27 files):           + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2

  C/C++:
    Built as dynamic libs?:      NO
    C++ Compiler:                C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/x86_amd64/cl.exe  (ver 19.0.24241.7)
    C++ flags (Release):         /DWIN32 /D_WINDOWS /W4 /GR  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /fp:precise     /EHa /wd4127 /wd4251 /wd4324 /wd4275 /wd4512 /wd4589 /MP2
 /MT /O2 /Ob2 /DNDEBUG
    C++ flags (Debug):           /DWIN32 /D_WINDOWS /W4 /GR  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /fp:precise     /EHa /wd4127 /wd4251 /wd4324 /wd4275 /wd4512 /wd4589 /MP2
 /MTd /Zi /Ob0 /Od /RTC1
    C Compiler:                  C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC/bin/x86_amd64/cl.exe
    C flags (Release):           /DWIN32 /D_WINDOWS /W3  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /fp:precise       /MP2    /MT /O2 /Ob2 /DNDEBUG
    C flags (Debug):             /DWIN32 /D_WINDOWS /W3  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /fp:precise       /MP2  /MTd /Zi /Ob0 /Od /RTC1
    Linker flags (Release):      /machine:x64  /NODEFAULTLIB:atlthunk.lib /INCREMENTAL:NO  /NODEFAULTLIB:libcmtd.lib /NODEFAULTLIB:libcpmtd.lib /NODEFAULTLIB:msvcrtd.lib
    Linker flags (Debug):        /machine:x64  /NODEFAULTLIB:atlthunk.lib /debug /INCREMENTAL  /NODEFAULTLIB:libcmt.lib /NODEFAULTLIB:libcpmt.lib /NODEFAULTLIB:msvcrt.lib
    ccache:                      NO
    Precompiled headers:         YES
    Extra dependencies:          ade comctl32 gdi32 ole32 setupapi ws2_32
    3rdparty dependencies:       ittnotify libprotobuf zlib libjpeg-turbo libwebp libpng libtiff libjasper IlmImf quirc ippiw ippicv
  OpenCV modules:
    To be built:                 calib3d core dnn features2d flann gapi highgui imgcodecs imgproc ml objdetect photo python3 stitching video videoio
    Disabled:                    world
    Disabled by dependency:      -
    Unavailable:                 java js python2 ts
    Applications:                -
    Documentation:               NO
    Non-free algorithms:         NO
  Windows RT support:            NO
  GUI:
    Win32 UI:                    YES
    VTK support:                 NO
  Media I/O:
    ZLib:                        build (ver 1.2.11)
    JPEG:                        build-libjpeg-turbo (ver 2.0.2-62)
    WEBP:                        build (ver encoder: 0x020e)
    PNG:                         build (ver 1.6.37)
    TIFF:                        build (ver 42 - 4.0.10)
    JPEG 2000:                   build (ver 1.900.1)
    OpenEXR:                     build (ver 2.3.0)
    HDR:                         YES
    SUNRASTER:                   YES
    PXM:                         YES
    PFM:                         YES
  Video I/O:
    DC1394:                      NO
    FFMPEG:                      YES (prebuilt binaries)
      avcodec:                   YES (58.35.100)
      avformat:                  YES (58.20.100)
      avutil:                    YES (56.22.100)
      swscale:                   YES (5.3.100)
      avresample:                YES (4.0.0)
    GStreamer:                   NO
    DirectShow:                  YES
    Media Foundation:            YES
      DXVA:                      NO
  Parallel framework:            Concurrency
  Trace:                         YES (with Intel ITT)
  Other third-party libraries:
    Intel IPP:                   2019.0.0 Gold [2019.0.0]
           at:                   C:/projects/opencv-python/_skbuild/win-amd64-3.6/cmake-build/3rdparty/ippicv/ippicv_win/icv
    Intel IPP IW:                sources (2019.0.0)
              at:                C:/projects/opencv-python/_skbuild/win-amd64-3.6/cmake-build/3rdparty/ippicv/ippicv_win/iw
    Lapack:                      NO
    Eigen:                       NO
    Custom HAL:                  NO
    Protobuf:                    build (3.5.1)
  OpenCL:                        YES (NVD3D11)
    Include path:                C:/projects/opencv-python/opencv/3rdparty/include/opencl/1.2
    Link libraries:              Dynamic load
  Python 3:
    Interpreter:                 C:/Python36-x64/python.exe (ver 3.6.8)
    Libraries:                   C:/Python36-x64/libs/python36.lib (ver 3.6.8)
    numpy:                       C:/Python36-x64/lib/site-packages/numpy/core/include (ver 1.11.3)
    install path:                python  
  Python (for build):            C:/Python27-x64/python.exe
  Java:
    ant:                         NO
    JNI:                         C:/Program Files/Java/jdk1.8.0/include C:/Program Files/Java/jdk1.8.0/include/win32 C:/Program Files/Java/jdk1.8.0/include
    Java wrappers:               NO
    Java tests:                  NO

Install to: C:/projects/opencv-python/_skbuild/win-amd64-3.6/cmake-install

Thank you.

Answer 1

Put a wait key at the end of your code, as follow, in order to show video frames before the re-execution of the same code.

import numpy as np 
from cv2 import cv2  
cap = cv2.VideoCapture(0)
while True:
    ret, frame = cap.read()
    cv2.imshow('frame', frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

I hope it will work.

Answer 2

You don't need to grand access openCV to your webcam. If you have any antivirus software, please check the setting for webcam access. By the way, could you try to run the code below?

import numpy as np 
import cv2

cap = cv2.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # Our operations on the frame come here
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_gui/py_video_display/py_video_display.html