Deteksi wajah merupakan tahapan awal dalam sistem pengenalan wajah. Sistem pengenalan wajah banyak diaplikasikan dalam bidang biometrik untuk mengenali identitas pemilik wajah.

Berikut ini merupakan contoh aplikasi pemrograman matlab untuk mendeteksi wajah (face detection).

faceDetector = vision.CascadeObjectDetector;
I = imread('visionteam.jpg');
bboxes = step(faceDetector, I);
IFaces = insertObjectAnnotation(I, 'rectangle', bboxes, 'Face');
figure, imshow(IFaces), title('Detected faces');

Upper Body detection

I2 = imread('visionteam.jpg');
bodyDetector = vision.CascadeObjectDetector('UpperBody');
bodyDetector.MinSize = [60 60];
bodyDetector.MergeThreshold = 10;
bboxBody = step(bodyDetector, I2);
IBody = insertObjectAnnotation(I2, 'rectangle',bboxBody,'Upper Body');
figure, imshow(IBody), title('Detected upper bodies');

Koding tersebut menggunakan algoritma viola-jones yang dapat diaplikasikan pada wajah yang menghadap ke depan (frontal face) dan dalam posisi tegak. Proses deteksi wajah dapat ditampilkan dalam bentuk GUI melalui pemrograman berikut:

function varargout = facedetection(varargin)
% FACEDETECTION MATLAB code for facedetection.fig
%      FACEDETECTION, by itself, creates a new FACEDETECTION or raises the existing
%      singleton*.
%
%      H = FACEDETECTION returns the handle to a new FACEDETECTION or the handle to
%      the existing singleton*.
%
%      FACEDETECTION('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in FACEDETECTION.M with the given input arguments.
%
%      FACEDETECTION('Property','Value',...) creates a new FACEDETECTION or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before facedetection_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to facedetection_OpeningFcn via varargin.
%
%      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
%      instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES

% Edit the above text to modify the response to help facedetection

% Last Modified by GUIDE v2.5 02-Jan-2014 17:33:58

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
    'gui_Singleton',  gui_Singleton, ...
    'gui_OpeningFcn', @facedetection_OpeningFcn, ...
    'gui_OutputFcn',  @facedetection_OutputFcn, ...
    'gui_LayoutFcn',  [] , ...
    'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end

if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT


% --- Executes just before facedetection is made visible.
function facedetection_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to facedetection (see VARARGIN)

% Choose default command line output for facedetection
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);
movegui(hObject, 'center');
clc
clear

% UIWAIT makes facedetection wait for user response (see UIRESUME)
% uiwait(handles.figure1);


% --- Outputs from this function are returned to the command line.
function varargout = facedetection_OutputFcn(hObject, eventdata, handles)
% varargout  cell array for returning output args (see VARARGOUT);
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Get default command line output from handles structure
varargout{1} = handles.output;

reqToolboxes = {'Computer Vision System Toolbox', 'Image Processing Toolbox'};
info = ver;
s=size(info);

flg = zeros(size(reqToolboxes));
reqSize = size(reqToolboxes,2);

for i=1:s(2)
    for j=1:reqSize
        if( strcmpi(info(1,i).Name,reqToolboxes{1,j}) )
            flg(1,j)=1;
        end
    end
end
ret = prod(flg);

if ~ret
    error('detectFaceParts requires: Computer Vision System Toolbox and Image Processing Toolbox. Please install these toolboxes.');
end

% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
[filename,pathname]=uigetfile('*.*');
if ~isequal(filename,0)
    handles.data1 = imread(fullfile(pathname,filename));
    guidata(hObject,handles);
    axes(handles.axes1)
    cla reset
    imshow(handles.data1);
else
    return
end

% --- Executes on button press in pushbutton2.
function pushbutton2_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton2 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
tic
X = handles.data1;
thresholdFace = 1;
thresholdParts = 1;
stdsize = 176;

nameDetector = {'LeftEye'; 'RightEye'; 'Mouth'; 'Nose'; };
mins = [[12 18]; [12 18]; [15 25]; [15 18]; ];

detector.stdsize = stdsize;
detector.detector = cell(5,1);
for k=1:4
    minSize = int32([stdsize/5 stdsize/5]);
    minSize = [max(minSize(1),mins(k,1)), max(minSize(2),mins(k,2))];
    detector.detector{k} = vision.CascadeObjectDetector(char(nameDetector(k)), 'MergeThreshold', thresholdParts, 'MinSize', minSize);
end

detector.detector{5} = vision.CascadeObjectDetector('FrontalFaceCART', 'MergeThreshold', thresholdFace);

%%%%%%%%%%%%%%%%%%%%%%% detect face %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Detect faces
bbox = step(detector.detector{5}, X);

bbsize = size(bbox);
partsNum = zeros(size(bbox,1),1);

%%%%%%%%%%%%%%%%%%%%%%% detect parts %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
stdsize = detector.stdsize;

for k=1:4
    if( k == 1 )
        region = [1,int32(stdsize*2/3); 1, int32(stdsize*2/3)];
    elseif( k == 2 )
        region = [int32(stdsize/3),stdsize; 1, int32(stdsize*2/3)];
    elseif( k == 3 )
        region = [1,stdsize; int32(stdsize/3), stdsize];
    elseif( k == 4 )
        region = [int32(stdsize/5),int32(stdsize*4/5); int32(stdsize/3),stdsize];
    else
        region = [1,stdsize;1,stdsize];
    end
    
    bb = zeros(bbsize);
    for i=1:size(bbox,1)
        XX = X(bbox(i,2):bbox(i,2)+bbox(i,4)-1,bbox(i,1):bbox(i,1)+bbox(i,3)-1,:);
        XX = imresize(XX,[stdsize, stdsize]);
        XX = XX(region(2,1):region(2,2),region(1,1):region(1,2),:);
        
        b = step(detector.detector{k},XX);
        
        if( size(b,1) > 0 )
            partsNum(i) = partsNum(i) + 1;
            
            if( k == 1 )
                b = sortrows(b,1);
            elseif( k == 2 )
                b = flipud(sortrows(b,1));
            elseif( k == 3 )
                b = flipud(sortrows(b,2));
            elseif( k == 4 )
                b = flipud(sortrows(b,3));
            end
            
            ratio = double(bbox(i,3)) / double(stdsize);
            b(1,1) = int32( ( b(1,1)-1 + region(1,1)-1 ) * ratio + 0.5 ) + bbox(i,1);
            b(1,2) = int32( ( b(1,2)-1 + region(2,1)-1 ) * ratio + 0.5 ) + bbox(i,2);
            b(1,3) = int32( b(1,3) * ratio + 0.5 );
            b(1,4) = int32( b(1,4) * ratio + 0.5 );
            
            bb(i,:) = b(1,:);
        end
    end
    bbox = [bbox,bb];
end


%%%%%%%%%%%%%%%%%%%%%%% draw faces %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
bbox = [bbox,partsNum];
bbox(partsNum<=2,:)=[];

face =  bbox(:,1: 4);
axes(handles.axes2)
cla reset
imshow(X);
hold on

[m, ~] = size(face);
for j = 1:m
    rectangle('Position',[face(j,1),face(j,2),face(j,3),face(j,4)],'EdgeColor','y','LineWidth',2);
end
hold off
toc
% for k = 1:m
%     imcrop(X,[face(k,1),face(k,2),face(k,3),face(k,4)]);
% end
    
% --- Executes on button press in pushbutton3.
function pushbutton3_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton3 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
img = getframe(gca);
[filename2,pathname2] = uiputfile(...
    {'*.bmp','bitmap image (*.bmp)';
    '*.jpg','jpeg image(*.bmp)';
    '*.*','All file(*.*)'},...
    'Save Image');
if ~isequal(filename2,0)
    imwrite(img.cdata,fullfile(pathname2,filename2));
else
    return
end

Sedangkan tampilan GUI nya adalah:

1. Membuka tampilan GUI awal

2. Melakukan deteksi wajah pada frontal face 1

3. Melakukan deteksi wajah pada frontal face 2

4. Melakukan deteksi wajah pada frontal face 3

5. Melakukan deteksi wajah pada frontal face 4

6. Melakukan deteksi wajah pada frontal face 5

File source code GUI lengkap beserta citra untuk deteksi wajah dengan algoritma viola-jones dapat diperoleh melalui halaman berikut ini: Source Code