video.py OpenCv例程阅读

 #!/usr/bin/env python

 '''
 Video capture sample.

 Sample shows how VideoCapture class can be used to acquire video
 frames from a camera of a movie file. Also the sample provides
 an example of procedural video generation by an object, mimicking
 the VideoCapture interface (see Chess class).

 'create_capture' is a convinience function for capture creation,
 falling back to procedural video in case of error.

 Usage:
     video.py [--shotdir <shot path>] [source0] [source1] ...'

     sourceN is an
      - integer number for camera capture
      - name of video file
      - synth:<params> for procedural video

 Synth examples:
     synth:bg=../cpp/lena.jpg:noise=0.1
     synth:class=chess:bg=../cpp/lena.jpg:noise=0.1:size=640x480

 Keys:
     ESC    - exit
     SPACE  - save current frame to <shot path> directory

 '''

 import numpy as np
 import cv2
 from time import clock
 from numpy import pi, sin, cos
 import common

 class VideoSynthBase(object):
     def __init__(self, size=None, noise=0.0, bg = None, **params):
         self.bg = None
         self.frame_size = (640, 480)
         if bg is not None:
             self.bg = cv2.imread(bg, 1)
             h, w = self.bg.shape[:2]
             self.frame_size = (w, h)

         if size is not None:
             w, h = map(int, size.split('x'))
             self.frame_size = (w, h)
             self.bg = cv2.resize(self.bg, self.frame_size)

         self.noise = float(noise)

     def render(self, dst):
         pass

     def read(self, dst=None):
         w, h = self.frame_size

         if self.bg is None:
             buf = np.zeros((h, w, 3), np.uint8)
         else:
             buf = self.bg.copy()

         self.render(buf)

         if self.noise > 0.0:
             noise = np.zeros((h, w, 3), np.int8)
             cv2.randn(noise, np.zeros(3), np.ones(3)*255*self.noise)
             buf = cv2.add(buf, noise, dtype=cv2.CV_8UC3)
         return True, buf

     def isOpened(self):
         return True

 class Chess(VideoSynthBase):
     def __init__(self, **kw):
         super(Chess, self).__init__(**kw)

         w, h = self.frame_size

         self.grid_size = sx, sy = 10, 7
         white_quads = []
         black_quads = []
         for i, j in np.ndindex(sy, sx):
             q = [[j, i, 0], [j+1, i, 0], [j+1, i+1, 0], [j, i+1, 0]]
             [white_quads, black_quads][(i + j) % 2].append(q)
         self.white_quads = np.float32(white_quads)
         self.black_quads = np.float32(black_quads)

         fx = 0.9
         self.K = np.float64([[fx*w, 0, 0.5*(w-1)],
                         [0, fx*w, 0.5*(h-1)],
                         [0.0,0.0,      1.0]])

         self.dist_coef = np.float64([-0.2, 0.1, 0, 0])
         self.t = 0

     def draw_quads(self, img, quads, color = (0, 255, 0)):
         img_quads = cv2.projectPoints(quads.reshape(-1, 3), self.rvec, self.tvec, self.K, self.dist_coef) [0]
         img_quads.shape = quads.shape[:2] + (2,)
         for q in img_quads:
             cv2.fillConvexPoly(img, np.int32(q*4), color, cv2.CV_AA, shift=2)

     def render(self, dst):
         t = self.t
         self.t += 1.0/30.0

         sx, sy = self.grid_size
         center = np.array([0.5*sx, 0.5*sy, 0.0])
         phi = pi/3 + sin(t*3)*pi/8
         c, s = cos(phi), sin(phi)
         ofs = np.array([sin(1.2*t), cos(1.8*t), 0]) * sx * 0.2
         eye_pos = center + np.array([cos(t)*c, sin(t)*c, s]) * 15.0 + ofs
         target_pos = center + ofs

         R, self.tvec = common.lookat(eye_pos, target_pos)
         self.rvec = common.mtx2rvec(R)

         self.draw_quads(dst, self.white_quads, (245, 245, 245))
         self.draw_quads(dst, self.black_quads, (10, 10, 10))

 classes = dict(chess=Chess)

 presets = dict(
     empty = 'synth:',
     lena = 'synth:bg=../cpp/lena.jpg:noise=0.1',
     chess = 'synth:class=chess:bg=../cpp/lena.jpg:noise=0.1:size=640x480'
 )

 def create_capture(source = 0, fallback = presets['chess']):
     '''source: <int> or '<int>|<filename>|synth [:<param_name>=<value> [:...]]'
     '''
     source = str(source).strip()
     chunks = source.split(':')
     # hanlde drive letter ('c:', ...)
     if len(chunks) > 1 and len(chunks[0]) == 1 and chunks[0].isalpha():
         chunks[1] = chunks[0] + ':' + chunks[1]
         del chunks[0]

     source = chunks[0]
     try: source = int(source)
     except ValueError: pass
     params = dict( s.split('=') for s in chunks[1:] )

     cap = None
     if source == 'synth':
         Class = classes.get(params.get('class', None), VideoSynthBase)
         try: cap = Class(**params)
         except: pass
     else:
         cap = cv2.VideoCapture(source)
         if 'size' in params:
             w, h = map(int, params['size'].split('x'))
             cap.set(cv2.cv.CV_CAP_PROP_FRAME_WIDTH, w)
             cap.set(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT, h)
     if cap is None or not cap.isOpened():
         print 'Warning: unable to open video source: ', source
         if fallback is not None:
             return create_capture(fallback, None)
     return cap

 if __name__ == '__main__':
     import sys
     import getopt

     print __doc__

     args, sources = getopt.getopt(sys.argv[1:], '', 'shotdir=')
     args = dict(args)
     shotdir = args.get('--shotdir', '.')
     if len(sources) == 0:
         sources = [ 0 ]

     caps = map(create_capture, sources)
     shot_idx = 0
     while True:
         imgs = []
         for i, cap in enumerate(caps):
             ret, img = cap.read()
             imgs.append(img)
             cv2.imshow('capture %d' % i, img)
         ch = 0xFF & cv2.waitKey(1)
         if ch == 27:
             break
         if ch == ord(' '):
             for i, img in enumerate(imgs):
                 fn = '%s/shot_%d_%03d.bmp' % (shotdir, i, shot_idx)
                 cv2.imwrite(fn, img)
                 print fn, 'saved'
             shot_idx += 1
     cv2.destroyAllWindows()

第133行：create_capture(source = 0, fallback = presets['chess'])        有两个参数 source 用于指示在哪里获取视频源。fallback ------------

　　　　

　　声明：s为字符串，rm为要删除的字符序列

　　s.strip(rm)        删除s字符串中开头、结尾处，位于 rm删除序列的字符

　　s.lstrip(rm)       删除s字符串中开头处，位于 rm删除序列的字符

　　s.rstrip(rm)      删除s字符串中结尾处，位于 rm删除序列的字符

　　当rm为空时，默认删除空白符（包括'\n', '\r',  '\t',  ' ')

总结 开启数据采集设备并返回 控制句柄。