----------------------------边学边写边学习-------------------------------------
版本：2014a
调用摄像头
a = imaqhwinfo
如果出现下面的警告说明你没安装扩展工具。
警告: No Image Acquisition adaptors found. Image acquisition adaptors may be available as downloadable support packages. Open Support Package Installer to install additional vendors.
这时候Support Package Installer在MATLAB里面有下划线，然后你点开它，MATLAB会提供大概13个软件包，这时候选择OS Generic Video Interface下载安装就OK了 （要求注册账号，随便用个邮箱注册下就可以了，不需要付费）。
（matlab查看摄像头详细信息 请看 https://blog.csdn.net/hmg25/article/details/4126122 ）
下面就是调用笔记本电脑摄像头并打开图像
（%如果使用USB摄像头，一般为2，笔记本自带摄像头为1）
vidDevice = imaq.VideoDevice(\'winvideo\', 1, \'YUY2_640x480\', ...
\'ROI\', [1 1 640 480], ...
\'ReturnedColorSpace\', \'rgb\' );
preview(vidDevice);
人脸检测我们用的是matlab的机器视觉工具箱（瞬间觉得matlab真心强大）
VJ算法的目的是检测人脸，但是其思想同样可以用于检测其他物体，只需进行训练即可。
VJ算法在Matlab里面实现的时候，已经训练好了正脸、侧脸、上半身、眼睛、嘴、鼻子，这些都是可以直接检测，不需训练，直接调用CascadeObjectDetector函数即可。
下面是检测人脸和上半身的例子
% Example 1: Face detection
% ----------------------------
faceDetector = vision.CascadeObjectDetector; % Default: finds faces
I = imread(\'visionteam.jpg\');
bboxes = step(faceDetector, I); % Detect faces
% Annotate detected faces
IFaces = insertObjectAnnotation(I, \'rectangle\', bboxes, \'Face\');
figure, imshow(IFaces), title(\'Detected faces\');
% Example 2: Upper body detection
% --------------------------------------
bodyDetector = vision.CascadeObjectDetector(\'UpperBody\');
bodyDetector.MinSize = [60 60];
bodyDetector.MergeThreshold = 10;
I2 = imread(\'visionteam.jpg\');
bboxBody = step(bodyDetector, I2); % Detect upper bodies
% Annotate detected upper bodies
IBody = insertObjectAnnotation(I2, \'rectangle\', ...
bboxBody, \'Upper Body\');
figure, imshow(IBody), title(\'Detected upper bodies\');
至于调用摄像头进行人脸识别，肯定是 调用摄像头的过程中对每一帧图像分别进行识别，然后再在图像中框出来。
这就要求 速度 要足够快。所以检测的时候就要压缩你图像的像素了。
下面放代码
faceDetector = vision.CascadeObjectDetector(); %enable viola jones algorithm
bbox = [100 100 100 100];
vidDevice = imaq.VideoDevice(\'winvideo\', 1, \'YUY2_640x480\', ...
\'ROI\', [1 1 640 480], ...
\'ReturnedColorSpace\', \'rgb\' );
%set(vidDevice.DeviceProperties, \'FrameRate\', \'30\');
boxInserter = vision.ShapeInserter(\'BorderColor\',\'Custom\',...
\'CustomBorderColor\',[255 255 0]);
textInserter = vision.TextInserter(\'%d\',\'LocationSource\',\'Input port\',\'Color\',[255,255, 0],\'FontSize\',12);
nFrame =300;
vidInfo = imaqhwinfo(vidDevice);
vidHeight = vidInfo.MaxHeight;
vidWidth = vidInfo.MaxWidth;
videoPlayer = vision.VideoPlayer(\'Position\',[300 100 640+30 480+30]);
for k = 1:nFrame % start recording with 300 frames
%tic; % timer start
videoFrame = step(vidDevice); % enable the image capture by webcam
bbox = 4 * faceDetector.step(imresize(videoFrame, 1/4)); % boost video\'s fps
videoOut = step(boxInserter, videoFrame, bbox); % highlight the boxes of face at video
%release(boxInserter);
step(videoPlayer, videoOut); % display the video live in video player
end
一共执行了300帧，下面放图。
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