OpenCV3计算机视觉Python语言实现（二）:处理文件、摄像头和图形用户界面

• 2.1 基本I/O脚本
  
  • 2.1.1 读/写图像文件
  • 2.1.2 图像和原始字节之间的转换
  • 2.1.3使用numpy.array()访问图像数据
  • 2.1.4 视频文件的读写
  • 2.1.5 捕获摄像头的帧
  • 2.1.6 在窗口显示图像
  • 2.1.7 在窗口显示摄像头帧
• 2.2 Cameo项目（人脸跟踪和图像处理）
• 2.3 Cameo-面向对象设计

安装

从网址：http://www.lfd.uci.edu/~gohlke/pythonlibs/#opencv
下载opencv-whl文件

pip install wheelpip install ****.whl

　　大多数常用的OpenCV函数都在cv2模块中。可能会遇到其他基于cv2.cv模块的，这些都是传统版本，Python模块被成为cv2并不是表示该模块针对OpenCV2.x.x版本的，而是因为该模块引入了一个更好的API接口，它们采用了面向对象的编程方式，这与以前的cv模块有所不同，以前的cv模块更多采用面向过程化的编程方式。

2.1 基本的I/O脚本

2.1.1 读/写图像文件

　　OpenCV的imread()函数和imwrite()函数能支持各种静态图像文件。不管哪种格式，每个像素都会有一个值，但不同格式的表示像素的方式不同。如：通过numpy数组来创建一个黑色的正方形图像：

img=numpy.zeros((4,2),dtype=numpy.uint8)# dtype=uint8表示每个像素都由一个8位整数来表示，即每个像素值的范围是0~255

cv2.cvtColor函数：将该图像转换成BGR模式或者RGB模式

import cv2imgBGR=cv2.cvtColor(img,cv2.COLOR_GRAY2BGR)print imgBGR,imgBGR.shape# img.shape():返回HxWxC.img为4行2列的二维数组。imgBGR.shape=(4,2,3),4页*2行*3列，其中每一个行的3列分别代表BGR值或BGR值.

取值img[0,0,0]或img[0][0]：第一个值表示y坐标或行，0表示顶部；第二个值表示像素的x坐标或者列；第三个值表示颜色通道

# 图像的读取、显示、保存import cv2img=cv2.imread('lena.jpg')# 读取第二个参数表示以什么方式读入，将图像以灰度图像读入：cv2.imread('./lena.jpg',cv2.IMREAD_GRAYSCALE)第二个参数省略时，默认Opencv以BGR的格式读入cv2.imshow('lena_img',img)cv2.waitKey(0)# cv2.waitKey(0)是一个键盘绑定函数。需要指出的是它的时间尺度是毫秒级。函数等待特定的几毫秒，看是否有键盘输入。特定的几毫秒之内，如果按下任意键，这个函数会返回按键的ASCII码，程序会继续运行。如果没有键盘输入，返回为-1，如果我们设置这个函数的参数为0，那么会无限期的等待键盘输入。它也可以被用来检测特定键是都被按下。cv2.destoryAllWindows()# 关闭所有打开的窗口。也可以通过cv2.destoryWindows(windowsName)来关闭指定的窗口cv2.imwrite('lena2.png',img)# imwrite()要求图像为BGR或者灰度格式

2.1.2 图像和原始字节之间的转换:bytearray()函数

　　若一幅图像的通道有8位，则可将其显示转换成标准的一维Python bytearray格式：

import numpy as npbyteArray=bytearray(image)print len(byteArray) # 输出为HxWxC# 由字节转换成图像grayImage=np.array(byteArray).reshape(height,width)bgrImage=np.array(byteArray).reshape(height,width,3)# 随机生成字节import osrandomByteArray=bytearray(os.urandom(120000))flatNumpyArray=numpy.array(randomByteArray) # OpenCV图像是.array类型的二维或者三维数组，因此转换成array"bgrImage=flatNumpyArray.reshape(200,200,3)cv2.imshow("bgrImage",bgrImage)

2.1.3使用numpy.array()访问图像数据

访问数组中特定位置的值使用np.array()提供的item(),设置特定位置的值：itemset()

import cv2import numpy as nplenaImage = cv2.imread('lena.jpg')print lenaImage.item(150, 120, 0)// 访问特定位置lenaImage.itemset((150, 120, 0), 255) // 设置特定位置的值

通过循环处理数组的效率很低，采用索引的方式来解决这个问题：

import cv2import numpy as npimg = cv2.imread('lena.jpg') img[:,:,1]=0 img[:,:,1] = 0 // 将所有的G通道设置为0img[0:100,0:100,:] // 得到图像从左上角开始100*100的区域三个通道值img[0,0]=[0,0,0] // 将黑色BGR值赋给图像第0行第0列的三通道值

其他属性

print img.shape // 返回图像H，W，C的数组print img.size // 返回图像像素的大小print img.dtype // 得到图像的数据类型（通常为一个无符号整数类型的变量和该类型占的位数，比如uint8）

2.1.4 视频文件的读写

OpenCV提供了VideoCapture和VideoWriter类来支持各种视频的读写。在达到视频文件末尾之前，VideoCapture都会通过read()来获取新的一帧，每一帧都是基于BGR格式的图像；
可将一幅图像传递给VideoWriter类的write()函数，该函数会将这副图像加到VideoWriter类所指向的文件。

import cv2videoCapture = cv2.VideoCapture('meipai.mp4')fps = videoCapture.get(cv2.CAP_PROP_FPS)  # 帧速率，fps帧/秒size = (int(videoCapture.get(cv2.CAP_PROP_FRAME_WIDTH)), \        int(videoCapture.get(cv2.CAP_PROP_FRAME_HEIGHT)))print size  # (854,480)注意此时的size为WxHvideoWriter = cv2.VideoWriter('meipai.avi', cv2.VideoWriter_fourcc('I', '4', '2', '0'), fps, size)success, frame = videoCapture.read()print frame.shape  # (480,854,3) 此时为读取到的每一张图片大小HxWxCwhile success:  # success为bool型，当读到末尾的时候为空    videoWriter.write(frame)    success, frame = videoCapture.read()

videoWriter类的构造函数需要指定视频编解码器。编解码器根据系统的不同而不同，一下是常用的一些选项：

- cv2.VideoWriter_fourcc('I','4','2','0'):该选项是一个未压缩的YUV颜色编码，是4:2:0色度子采样。这种编码有很好的兼容性，但会产生较大的文件，扩展名为avi- cv2.VideoWriter_fourcc('P','I','M','1'):该选项是MPEG-1编码类型，扩展名为avi- cv2.VideoWriter_fourcc('X', 'V', 'I', 'D'):MPEG-4编码，如果希望得到的视频大小为平均值，推荐使用此选项，扩展名avi- cv2.VideoWriter_fourcc('T', 'H', 'E', 'O'):该选项是Ogg Vorbis,扩展名是avi- cv2.VideoWriter_fourcc('F', 'L', 'V', '1'):该选项是一个Flash视频，扩展名为.flv

2.1.5 捕获摄像头的帧

import cv2cameraCapture = cv2.VideoCapture(0)size = (int(cameraCapture.get(cv2.CAP_PROP_FRAME_WIDTH)), \        int(cameraCapture.get(cv2.CAP_PROP_FRAME_HEIGHT)))fps = 30  # 假定帧速率为30videoWriter = cv2.VideoWriter("MyOutputVideo.avi", \                              cv2.VideoWriter_fourcc("I", "4", "2", "0"), fps, size)success, frame = cameraCapture.read()numFrameRemaining = 10 * fps - 1while success and numFrameRemaining > 0:    videoWriter.write(frame)    success, frame = cameraCapture.read()    numFrameRemaining -= 1cameraCapture.release()

2.1.6 在窗口显示图像

2.1.7 在窗口显示摄像头帧

import cv2clicked = Falsedef onMouse(event, x, y, flags, param):    global clicked    if event == cv2.EVENT_LBUTTONUP:        clicked = TruecameraCapture = cv2.VideoCapture(0)cv2.namedWindow("MyWindow") #指定窗口名cv2.setMouseCallback("MyWindow", onMouse)#获取鼠标输入print "Showing camera feed. Click window or press any key to stop."success, frame = cameraCapture.read()while success and not clicked and cv2.waitKey(1) == -1:#没达到停止条件时    cv2.imshow("MyWindow", frame)    success, frame = cameraCapture.read()cv2.destroyAllWindows()cameraCapture.release()

• cv2.waitKey():获取键盘输入，参数为等待键触发的时间，单位毫秒，其返回值为-1（表示没有被键盘按下）或ASCII码。
• setMouseCallback()获取鼠标输入

opencv的窗口函数和waitKey函数相互以阿里。Opencv的窗口只有在调用waitKey函数时才会更新，waitkey函数只有在opencv窗口成为活动窗口时才能捕获输入信息。

在一些系统中，waitKey()的返回值可能比ASCII码的值更大（在Linux系统中，如果Opencv使用GTK作为后端的GUI库，就会出现一个众所周知的bug

在所有的系统中，可以通过读取返回值的最后一个字节来保证只提取ASCII码，具体代码如下：

keycode = cv2.waitKey(1)if keycode != -1:    keycode &= 0xFF

2.2-2.3 cameo项目（人脸跟踪和图像处理）

1.manager.py

manager.py# -*-coding:utf-8-*-import cv2from cv2 import *import numpyimport timeclass CaptureManager(object):    def __init__(self, capture, previewWindowManager=None, \                 shouldMirrorPreview=False):        self.previewWindowManager = previewWindowManager        self.shouldMirrorPreview = shouldMirrorPreview        # 注意大多数成员（member）变量为非公有变量，这类变量名前会加一个下划线进行标识。        self._capture = capture        self._channel = 0        self._enteredFrame = False        self._frame = None        self._imageFilename = None        self._videoFilename = None        self._videoEncoding = None        self._videoWriter = None        self._startTime = None        self._framesElapsed = long(0)        self._fpsEstimate = None    # 关于@符号的含义可以参考链接：https://www.zhihu.com/question/26930016    @property    def channel(self):        return self._channel    @channel.setter    def channel(self, value):        if self._channel != value:            self._channel = value            self._frame = None    @property    def frame(self):        if self._enteredFrame and self._frame is None:            _, self._frame = self._capture.retrieve()        return self._frame    @property    def isWritingImage(self):        return self._imageFilename is not None    @property    def isWritingVideo(self):        return self._videoFilename is not None    def enterFrame(self):        """Capture the next frame,if any."""        # But first ,check that any previous frame was exited.        assert not self._enteredFrame, 'previous enteredFrame() had no matching exitFrame()'        if self._capture is not None:            self._enteredFrame = self._capture.retrieve()    def exitFrame(self):        """Draw to the window,write to files,Release the frame."""        # Check whether ant grabbed frame is retrievable.        # The getter may retrieve and cache the frame        if self._frame is None:            self._enteredFrame = False            return        # Update the FPS estimate and related variables        if self._framesElapsed == 0:            self._startTime = time.time()        else:            timeElapsed = time.time() - self._startTime            self._fpsEstimate = int(self._framesElapsed / timeElapsed)        self._framesElapsed += 1        # Draw to the Window,if any.        if self.previewWindowManager is not None:            if self.shouldMirrorPreview:                mirroredFrame = numpy.fliplr(self._frame).copy()                self.previewWindowManager.show(mirroredFrame)            else:                self.previewWindowManager.show(self._frame)        # Write to the image file,if any.        if self.isWritingImage:            cv2.imwrite(self._imageFilename, self._frame)            self._imageFilename = None        # Write to the video file,if any.        self._writeVideoFrame()        # Release the Frame        self._frame = None        self._enteredFrame = False    def writeImage(self, filename):        """write the next exited frame to an image frame"""        self._imageFilename = filename    def startWritingVideo(self, filename, encoding=cv2.VideoWriter_fourcc("I", "4", "2", "0")):        """start writing exited frames to a video file"""        self._videoFilename = filename        self._videoEncoding = encoding        print self._videoEncoding    def stopWritingVideo(self):        """Stop writing exited frames to a video file"""        self._imageFilename = None        self._videoEncoding = None        self._videoWriter = None    def _writeVideoFrame(self):        if not self.isWritingVideo:            return        if self._videoWriter is None:            fps = self._capture.get(cv2.CAP_PROP_FPS)            if fps == 0.0:                # the capture fps is unknow ,so ues an estimate.                if self._framesElapsed < 20:                    # wait until more frames elapse so that the estimate is stable                    return                else:                    fps = self._fpsEstimate            size = (int(self._capture.get(cv2.CAP_PROP_FRAME_WIDTH)), \                    int(self._capture.get(cv2.CAP_PROP_FRAME_HEIGHT)))            # self._videoWriter = cv2.VideoWriter(self._videoFilename, self._videoEncoding, fps, size)            print "self._videoEncoding:",self._videoEncoding            self._videoWriter = cv2.VideoWriter(self._videoFilename, self._videoEncoding, fps, size)            print self._frame            self._videoWriter.write(self._frame)class WindowManager(object):    def __init__(self, windowName, keypressCallback=None):        self.keypressCallback = keypressCallback        self._windowName = windowName        self._isWindowCreated = False    @property    def isWindowCreated(self):        return self._isWindowCreated    def createdWindow(self):        cv2.namedWindow(self._windowName)        self._isWindowCreated = True    def show(self, frame):        cv2.imshow(self._windowName, frame)        # cv2.waitKey(1)    def destroyWindow(self):        cv2.destroyWindow(self._windowName)        self._isWindowCreated = False    def processEvents(self):        keycode = cv2.waitKey(1)        if self.keypressCallback is not None and keycode != -1:            # Discard any non-ASCII info encoded by GTK            keycode &= 0xFF            self.keypressCallback(keycode)

2.cameo.py

import cv2from managers import WindowManager, CaptureManagerimport filtersclass Cameo(object):    def __init__(self):        self._windowManger = WindowManager('Cameo', self.onKeypress)        self._captureManger = CaptureManager(cv2.VideoCapture(0), self._windowManger, True)        self._curveFilter=filters.BlurFilter()    def run(self):        """Run the main loop"""        self._windowManger.createdWindow()        while self._windowManger.isWindowCreated:            self._captureManger.enterFrame()            frame = self._captureManger.frame            filters.strokeEdges(frame,frame)            self._curveFilter.apply(frame,frame)            self._captureManger.exitFrame()            self._windowManger.processEvents()    def onKeypress(self, keycode):        """Handle a keypress.        space   -> Take a screenshot        tab     -> Start/stop recoding a screenshot        escape  -> Quit        """        if keycode == 32:  # space            self._captureManger.writeImage("./screenshot.png")        elif keycode == 9:  # tab            if not self._captureManger.isWritingVideo:                self._captureManger.startWritingVideo('./screenshot.avi')            else:                self._captureManger.stopWritingVideo()        elif keycode == 27:  # escape            self._windowManger.destroyWindow()if __name__ == '__main__':    Cameo().run()

这里出现一个问题，录制的视频大小不为0，但是时长总是0.不知道是什么原因？每一帧都被后一帧覆盖掉了？还不懂，还望懂的小伙伴不吝赐教。