如何使用Python和PyObjC从Apple iSight捕获帧？

Question

我想从使用Python（版本2.7或2.6）和PyObjC（版本2.2）内置到Macbook Pro中的Apple iSight摄像头捕获单帧。

作为一个起点，我用this old StackOverflow问题。为了验证它是有道理的，我交叉引用了它似乎基于的Apple's MyRecorder示例。不幸的是，我的脚本不起作用。

我的大问题是：

• 我是否正确初始化相机？
• 我开始正确的事件循环？
• 有没有其他设置我应该做的？

在下面粘贴的示例脚本中，预期的操作是在调用startImageCapture（）后，我应该开始打印CaptureDelegate的“Got a frame ...”消息。但是，相机的指示灯永远不会亮起，委托人的回叫从不执行。

另外，在startImageCapture（）中没有失败，所有函数声称成功，并且它成功找到iSight设备。分析pdb中的会话对象显示它具有有效的输入和输出对象，输出具有分配的委托，该设备未被其他进程使用，并且在调用startRunning（）之后会话被标记为正在运行。

下面的代码：

#!/usr/bin/env python2.7 

import sys 
import os 
import time 
import objc 
import QTKit 
import AppKit 
from Foundation import NSObject 
from Foundation import NSTimer 
from PyObjCTools import AppHelper 
objc.setVerbose(True) 

class CaptureDelegate(NSObject): 
    def captureOutput_didOutputVideoFrame_withSampleBuffer_fromConnection_(self, captureOutput, 
                      videoFrame, sampleBuffer, 
                      connection): 
     # This should get called for every captured frame 
     print "Got a frame: %s" % videoFrame 

class QuitClass(NSObject): 
    def quitMainLoop_(self, aTimer): 
     # Just stop the main loop. 
     print "Quitting main loop." 
     AppHelper.stopEventLoop() 


def startImageCapture(): 
    error = None 

    # Create a QT Capture session 
    session = QTKit.QTCaptureSession.alloc().init() 

    # Find iSight device and open it 
    dev = QTKit.QTCaptureDevice.defaultInputDeviceWithMediaType_(QTKit.QTMediaTypeVideo) 
    print "Device: %s" % dev 
    if not dev.open_(error): 
     print "Couldn't open capture device." 
     return 

    # Create an input instance with the device we found and add to session 
    input = QTKit.QTCaptureDeviceInput.alloc().initWithDevice_(dev) 
    if not session.addInput_error_(input, error): 
     print "Couldn't add input device." 
     return 

    # Create an output instance with a delegate for callbacks and add to session 
    output = QTKit.QTCaptureDecompressedVideoOutput.alloc().init() 
    delegate = CaptureDelegate.alloc().init() 
    output.setDelegate_(delegate) 
    if not session.addOutput_error_(output, error): 
     print "Failed to add output delegate." 
     return 

    # Start the capture 
    print "Initiating capture..." 
    session.startRunning() 


def main(): 
    # Open camera and start capturing frames 
    startImageCapture() 

    # Setup a timer to quit in 10 seconds (hack for now) 
    quitInst = QuitClass.alloc().init() 
    NSTimer.scheduledTimerWithTimeInterval_target_selector_userInfo_repeats_(10.0, 
                      quitInst, 
                      'quitMainLoop:', 
                      None, 
                      False) 
    # Start Cocoa's main event loop 
    AppHelper.runConsoleEventLoop(installInterrupt=True) 

    print "After event loop" 


if __name__ == "__main__": 
    main() 

感谢您的帮助，您可以提供！

Answer 1

好吧，我花了一天的时间在PyObjC的深处潜水，并让它工作。

对于将来的记录，问题中的代码不起作用的原因：变量作用域和垃圾回收。 会话变量在事件处理器运行之前发生的范围超出范围时被删除。必须做一些事情来保留它，以免在它有时间运行之前释放它。

将所有内容移动到类中，并使会话一个类变量使回调开始工作。此外，下面的代码演示了如何将帧的像素数据转换为位图格式并通过Cocoa调用保存它，以及如何将其作为缓冲区或字符串复制回Python的世界视图。

下面的脚本将捕获单个帧

#!/usr/bin/env python2.7 
# 
# camera.py -- by Trevor Bentley (02/04/2011) 
# 
# This work is licensed under a Creative Commons Attribution 3.0 Unported License. 
# 
# Run from the command line on an Apple laptop running OS X 10.6, this script will 
# take a single frame capture using the built-in iSight camera and save it to disk 
# using three methods. 
# 

import sys 
import os 
import time 
import objc 
import QTKit 
from AppKit import * 
from Foundation import NSObject 
from Foundation import NSTimer 
from PyObjCTools import AppHelper 

class NSImageTest(NSObject): 
    def init(self): 
     self = super(NSImageTest, self).init() 
     if self is None: 
      return None 

     self.session = None 
     self.running = True 

     return self 

    def captureOutput_didOutputVideoFrame_withSampleBuffer_fromConnection_(self, captureOutput, 
                      videoFrame, sampleBuffer, 
                      connection): 
     self.session.stopRunning() # I just want one frame 

     # Get a bitmap representation of the frame using CoreImage and Cocoa calls 
     ciimage = CIImage.imageWithCVImageBuffer_(videoFrame) 
     rep = NSCIImageRep.imageRepWithCIImage_(ciimage) 
     bitrep = NSBitmapImageRep.alloc().initWithCIImage_(ciimage) 
     bitdata = bitrep.representationUsingType_properties_(NSBMPFileType, objc.NULL) 

     # Save image to disk using Cocoa 
     t0 = time.time() 
     bitdata.writeToFile_atomically_("grab.bmp", False) 
     t1 = time.time() 
     print "Cocoa saved in %.5f seconds" % (t1-t0) 

     # Save a read-only buffer of image to disk using Python 
     t0 = time.time() 
     bitbuf = bitdata.bytes() 
     f = open("python.bmp", "w") 
     f.write(bitbuf) 
     f.close() 
     t1 = time.time() 
     print "Python saved buffer in %.5f seconds" % (t1-t0) 

     # Save a string-copy of the buffer to disk using Python 
     t0 = time.time() 
     bitbufstr = str(bitbuf) 
     f = open("python2.bmp", "w") 
     f.write(bitbufstr) 
     f.close() 
     t1 = time.time() 
     print "Python saved string in %.5f seconds" % (t1-t0) 

     # Will exit on next execution of quitMainLoop_() 
     self.running = False 

    def quitMainLoop_(self, aTimer): 
     # Stop the main loop after one frame is captured. Call rapidly from timer. 
     if not self.running: 
      AppHelper.stopEventLoop() 

    def startImageCapture(self, aTimer): 
     error = None 
     print "Finding camera" 

     # Create a QT Capture session 
     self.session = QTKit.QTCaptureSession.alloc().init() 

     # Find iSight device and open it 
     dev = QTKit.QTCaptureDevice.defaultInputDeviceWithMediaType_(QTKit.QTMediaTypeVideo) 
     print "Device: %s" % dev 
     if not dev.open_(error): 
      print "Couldn't open capture device." 
      return 

     # Create an input instance with the device we found and add to session 
     input = QTKit.QTCaptureDeviceInput.alloc().initWithDevice_(dev) 
     if not self.session.addInput_error_(input, error): 
      print "Couldn't add input device." 
      return 

     # Create an output instance with a delegate for callbacks and add to session 
     output = QTKit.QTCaptureDecompressedVideoOutput.alloc().init() 
     output.setDelegate_(self) 
     if not self.session.addOutput_error_(output, error): 
      print "Failed to add output delegate." 
      return 

     # Start the capture 
     print "Initiating capture..." 
     self.session.startRunning() 


    def main(self): 
     # Callback that quits after a frame is captured 
     NSTimer.scheduledTimerWithTimeInterval_target_selector_userInfo_repeats_(0.1, 
                       self, 
                       'quitMainLoop:', 
                       None, 
                       True) 

     # Turn on the camera and start the capture 
     self.startImageCapture(None) 

     # Start Cocoa's main event loop 
     AppHelper.runConsoleEventLoop(installInterrupt=True) 

     print "Frame capture completed." 

if __name__ == "__main__": 
    test = NSImageTest.alloc().init() 
    test.main() 

Answer 2

QTKit被弃用，PyObjC是一个很大的相关性（似乎是棘手的建立，如果你想在自制）。加上PyObjC没有大部分AVFoundation，所以我创建了a simple camera extension for Python，它使用AVFoundation来录制视频或捕捉图片，它不需要依赖（Cython中间文件承诺避免为大多数用户使用Cython）。

应该有可能建立这样的：

pip install -e git+https://github.com/dashesy/pyavfcam.git 

然后，我们可以用它来take a picture：

import pyavfcam 

# Open the default video source 
cam = pyavfcam.AVFCam(sinks='image') 
frame = cam.snap_picture('test.jpg') # frame is a memory buffer np.asarray(frame) can retrieve 

都没有涉及这个问题，但如果AVFCam类子分类，重写的方法将被调用，结果。