cv2.VideoCapture(0).read() 返回（假，无）
Posted
技术标签:
【中文标题】cv2.VideoCapture(0).read() 返回（假，无）【英文标题】：cv2.VideoCapture(0).read() returns (False, None) 【发布时间】：2020-11-05 06:58:03 【问题描述】：import cv2
cap=cv2.VideoCapture(0)
cap.set(3,640)#width
cap.set(4,480)#height
cap.set(10,100)#brightness
while True:
success, img = cap.read()
print(img)#getting None
print(success)#getting False
cv2.imshow("video", img)
cv2.waitKey(1)
if 0xFF == ord('q') :
break
VideoCapture 可以很好地处理 mp4 视频。但是当我尝试将它用于我的笔记本电脑网络摄像头时，它不起作用。 第一次使用 pyCharm 在我的笔记本电脑上运行此代码。 起初，网络摄像头本身没有打开。所以，我签入here 并在 /Applications/PyCharm\ CE.app/Contents/Info.plist 中添加了以下内容
<key>Privacy - Camera Usage</key>
<string>An application in PyCharm wants to use the camera</string>
当我运行代码时网络摄像头启动后，imshow 却返回 None。
Traceback (most recent call last):
File "/Users/sreeharsha/PycharmProjects/OpencvPython/chapter1.py", line 26, in <module>
cv2.imshow("video", img)
cv2.error: OpenCV(4.4.0) /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-req-build-4jcifzim/opencv/modules/highgui/src/window.cpp:376: error: (-215:Assertion failed) size.width>0 && size.height>0 in function 'imshow'
cap.isOpened() 返回 True 当我尝试 cap.getBackendName() 它返回以下错误
Traceback (most recent call last):
File "/Users/sreeharsha/PycharmProjects/OpencvPython/chapter1.py", line 16, in <module>
print(cap.getBackendName())
cv2.error: OpenCV(4.4.0) /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-req-build-4jcifzim/opencv/modules/videoio/src/cap.cpp:299: error: (-215:Assertion failed) api != 0 in function 'getBackendName'
cv2.getBuildInformation()如下
General configuration for OpenCV 4.4.0 =====================================
Version control: 4.4.0-dirty
Platform:
Timestamp: 2020-09-22T21:19:42Z
Host: Darwin 17.7.0 x86_64
CMake: 3.18.2
CMake generator: Unix Makefiles
CMake build tool: /usr/bin/make
Configuration: Release
CPU/HW features:
Baseline: SSE SSE2 SSE3 SSSE3 SSE4_1
requested: DETECT
Dispatched code generation: SSE4_2 FP16 AVX AVX2 AVX512_SKX
requested: SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
SSE4_2 (1 files): + POPCNT SSE4_2
FP16 (0 files): + POPCNT SSE4_2 FP16 AVX
AVX (4 files): + POPCNT SSE4_2 AVX
AVX2 (29 files): + POPCNT SSE4_2 FP16 FMA3 AVX AVX2
AVX512_SKX (4 files): + POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_COMMON AVX512_SKX
C/C++:
Built as dynamic libs?: NO
C++ standard: 11
C++ Compiler: /usr/local/opt/ccache/libexec/clang++ (ver 9.1.0.9020039)
C++ flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
C Compiler: /usr/local/opt/ccache/libexec/clang
C flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
Linker flags (Release): -Wl,-dead_strip
Linker flags (Debug): -Wl,-dead_strip
ccache: YES
Precompiled headers: NO
Extra dependencies: -framework OpenCL /Applications/Xcode-9.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Accelerate.framework -lm -ldl ade Qt5::Core Qt5::Gui Qt5::Widgets Qt5::Test Qt5::Concurrent openjp2
3rdparty dependencies: ittnotify libprotobuf zlib libjpeg-turbo libwebp libpng libtiff 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
GUI:
QT: YES (ver 5.13.2)
QT OpenGL support: NO
Cocoa: YES
VTK support: NO
Media I/O:
ZLib: build (ver 1.2.11)
JPEG: build-libjpeg-turbo (ver 2.0.5-62)
WEBP: build (ver encoder: 0x020f)
PNG: build (ver 1.6.37)
TIFF: build (ver 42 - 4.0.10)
JPEG 2000: OpenJPEG (ver 2.3.1)
OpenEXR: build (ver 2.3.0)
HDR: YES
SUNRASTER: YES
PXM: YES
PFM: YES
Video I/O:
DC1394: NO
FFMPEG: YES
avcodec: YES (58.91.100)
avformat: YES (58.45.100)
avutil: YES (56.51.100)
swscale: YES (5.7.100)
avresample: YES (4.0.0)
GStreamer: NO
AVFoundation: YES
Parallel framework: GCD
Trace: YES (with Intel ITT)
Other third-party libraries:
Intel IPP: 2020.0.0 Gold [2020.0.0]
at: /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-req-build-4jcifzim/_skbuild/macosx-10.13-x86_64-3.7/cmake-build/3rdparty/ippicv/ippicv_mac/icv
Intel IPP IW: sources (2020.0.0)
at: /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-req-build-4jcifzim/_skbuild/macosx-10.13-x86_64-3.7/cmake-build/3rdparty/ippicv/ippicv_mac/iw
Lapack: YES (/Applications/Xcode-9.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/Accelerate.framework -lm -ldl)
Eigen: YES (ver 3.3.7)
Custom HAL: NO
Protobuf: build (3.5.1)
OpenCL: YES (no extra features)
Include path: NO
Link libraries: -framework OpenCL
Python 3:
Interpreter: /Users/travis/build/skvark/opencv-python/venv/bin/python (ver 3.7.8)
Libraries: /Library/Frameworks/Python.framework/Versions/3.7/lib/libpython3.7m.dylib (ver 3.7.8)
numpy: /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-build-env-0spssg56/overlay/lib/python3.7/site-packages/numpy/core/include (ver 1.14.5)
install path: python
Python (for build): /System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7
Java:
ant: NO
JNI: /Applications/Xcode-9.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/JavaVM.framework/Headers /Applications/Xcode-9.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/JavaVM.framework/Headers /Applications/Xcode-9.4.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/System/Library/Frameworks/JavaVM.framework/Headers
Java wrappers: NO
Java tests: NO
Install to: /private/var/folders/nz/vv4_9tw56nv9k3tkvyszvwg80000gn/T/pip-req-build-4jcifzim/_skbuild/macosx-10.13-x86_64-3.7/cmake-install
-----------------------------------------------------------------
我也尝试使用各种 apiPreferences 创建 VideoCapture，但都失败了。
cap=cv2.VideoCapture(0, apiPreference=cv2.CAP_FFMPEG)
cap=cv2.VideoCapture(0, apiPreference=cv2.CAP_GSTREAMER)
cap=cv2.VideoCapture(0, apiPreference=cv2.CAP_V4L2)
请帮助我了解为什么会出现此问题以及如何解决此问题。
【问题讨论】：
【参考方案1】：您还需要根据this 来检查帧是否被正确读取，尝试 vidcap，如下代码 sn-p：
import cv2
cap=cv2.VideoCapture(0, cv2.CAP_V4L)
cap.set(3,640)#width
cap.set(4,480)#height
cap.set(10,100)#brightness
while True:
success, img = cap.read()
if success:
print(img)#getting None
print(success)#getting False
cv2.imshow("video", img)
cv2.waitKey(1)
if 0xFF == ord('q') :
break
【讨论】：
我总是以 False 获得成功。所以，框架没有被正确读取。会是什么原因？以上是关于cv2.VideoCapture(0).read() 返回（假，无）的主要内容，如果未能解决你的问题，请参考以下文章
机器学习进阶-图像基本处理-视频的读取与处理 1.cv2.VideoCapture(视频的载入) 2.vc.isOpened(载入的视频是否可以打开) 3.vc.read(视频中一张图片的读取)
无法在 Android 手机中使用 cv2.VideoCapture(0) 打开相机
VideoCapture 似乎不适用于 Debian - opencv 3.2