Apakah tujuan kompresi citra??

Kompresi atau pemampatan citra bertujuan untuk mereduksi atau memperkecil ukuran file citra. Dalam kompresi citra dikenal dua buah algoritma yaitu kompresi lossless dan kompresi lossy. Pada kompresi lossless memungkinkan citra asli dapat disusun kembali secara utuh dari citra hasil kompresi. Sedangkan pada kompresi lossy akan lebih banyak data yang hilang ketika penyusunan kembali dari citra hasil kompresi ke citra asli.

Berikut ini merupakan contoh aplikasi pemrograman matlab untuk melakukan kompresi lossless pada citra digital. Tahapan kompresi yang dilakukan ditunjukkan pada gambar flowchart berikut ini:

Langkah-langkah pemrograman untuk melakukan kompresi lossless pada citra digital adalah sebagai berikut:

1. Membaca file citra asli

% menampilkan menu browse file
[file, path] = uigetfile({'*.bmp;*.jpg;*.png;*.tiff;';'*.*'},...
'Select an Image File');

% jika ada file citra yang dipilih maka akan mengeksekusi perintah di
% bawahnya
if ~isequal(file,0)
% membaca file citra yang dipilih
Img = imread(fullfile(path,file));
% melihat ukuran file citra dalam satuan kb
fileinfo = imfinfo(file);
SIZE = fileinfo.FileSize;
Size = SIZE/1024;
% menampilkan ukuran file citra dalam satuan kb
set(handles.edit3,'String',[Size,' kb']);
% menampilkan file citra ke dalam axes
imshow(Img,'Parent', handles.axes1)
% menyimpan variabel Img dan fileinfo pada lokasi handles (lokasi
% penyimpanan variabel dalam MATLAB) agar dapat dipanggil oleh
% pushbutton yang lain
handles.Img = Img;
handles.fileinfo = fileinfo;
guidata(hObject, handles)
% mereset button2
axes(handles.axes2)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])
set(handles.pushbutton2,'Enable','on')
set(handles.pushbutton3,'Enable','off')
set(handles.edit1,'String',[])
set(handles.edit2,'String',[])
set(handles.edit4,'String',[])
set(handles.edit5,'String',[])
% jika tidak ada file citra yang dipilih maka akan kembali
else
return
end

2. Melakukan kompresi lossless terhadap citra asli

% memanggil variabel Img dan fileinfo yang ada pada lokasi handles
Img = handles.Img;
fileinfo = handles.fileinfo;

% melakukan lossless kompresi terhadap citra asli
Img_comp = zeros(size(Img));
for n = 1:3
I = Img(:,:,n);
T = dctmtx(8);
B = blkproc(I,[8 8],'P1*x*P2',T,T');
mask = [1   1   1   1   0   0   0   0
1   1   1   0   0   0   0   0
1   1   0   0   0   0   0   0
1   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0];
B2 = blkproc(B,[8 8],'P1.*x',mask);
Img_comp(:,:,n) = blkproc(B2,[8 8],'P1*x*P2',T',T);
end

% menyimpan file citra hasil kompresi
file_comp = ['Hasil Kompresi.',fileinfo.Format];
imwrite(Img_comp,file_comp);
% melihat ukuran file citra hasil kompresi dalam satuan kb
fileinfo_comp = imfinfo(file_comp);
SIZE = fileinfo_comp.FileSize;
Size = SIZE/1024;
% menampilkan ukuran file citra hasil kompresi dalam satuan kb
set(handles.edit4,'string',[Size,' kb']);
% menampilkan file citra hasil kompresi ke dalam axes
imshow(Img_comp,'Parent',handles.axes2)

% mereset button2
set(handles.pushbutton3,'Enable','on')
set(handles.edit1,'String',[])
set(handles.edit2,'String',[])
set(handles.edit5,'String',[])

% menyimpan variabel Img_comp dan fileinfo_comp pada lokasi handles (lokasi
% penyimpanan variabel dalam MATLAB) agar dapat dipanggil oleh
% pushbutton yang lain
handles.Img_comp = Img_comp;
handles.fileinfo_comp = fileinfo_comp;
guidata(hObject, handles)

3. Menghitung nilai PSNR, MSE, dan persentase kompresi

% memanggil variabel Img, fileinfo, Img_comp, dan fileinfo_comp yang ada
% pada lokasi handles
Img = handles.Img;
fileinfo = handles.fileinfo;
Img_comp = handles.Img_comp;
fileinfo_comp = handles.fileinfo_comp;

% menghitung nilai PSNR, MSE, dan % kompresi
nilai_psnr = psnr(Img,Img_comp);
nilai_mse = mse(Img,Img_comp);
filesize = fileinfo.FileSize;
filesize_comp = fileinfo_comp.FileSize;
persen_kompresi = filesize_comp/filesize*100;
% menampilkan nilai PSNR, MSE, dan % kompresi pada edit text
set(handles.edit1,'String',nilai_psnr)
set(handles.edit2,'String',nilai_mse)
set(handles.edit5,'String',persen_kompresi)

4. Melakukan kompresi terhadap file citra yang lain

Source code GUI pada pemrograman di atas adalah sebagai berikut:

function varargout = kompresi_citra(varargin)
% KOMPRESI_CITRA MATLAB code for kompresi_citra.fig
%      KOMPRESI_CITRA, by itself, creates a new KOMPRESI_CITRA or raises the existing
%      singleton*.
%
%      H = KOMPRESI_CITRA returns the handle to a new KOMPRESI_CITRA or the handle to
%      the existing singleton*.
%
%      KOMPRESI_CITRA('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in KOMPRESI_CITRA.M with the given input arguments.
%
%      KOMPRESI_CITRA('Property','Value',...) creates a new KOMPRESI_CITRA or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before kompresi_citra_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to kompresi_citra_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 kompresi_citra

% Last Modified by GUIDE v2.5 01-Nov-2018 12:43:14

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
'gui_Singleton',  gui_Singleton, ...
'gui_OpeningFcn', @kompresi_citra_OpeningFcn, ...
'gui_OutputFcn',  @kompresi_citra_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 kompresi_citra is made visible.
function kompresi_citra_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 kompresi_citra (see VARARGIN)

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

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

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

% --- Outputs from this function are returned to the command line.
function varargout = kompresi_citra_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;

function edit4_Callback(hObject, eventdata, handles)
% hObject    handle to edit4 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit4 as text
%        str2double(get(hObject,'String')) returns contents of edit4 as a double

% --- Executes during object creation, after setting all properties.
function edit4_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit4 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end

function edit3_Callback(hObject, eventdata, handles)
% hObject    handle to edit3 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit3 as text
%        str2double(get(hObject,'String')) returns contents of edit3 as a double

% --- Executes during object creation, after setting all properties.
function edit3_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit3 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
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)

% menampilkan menu browse file
[file, path] = uigetfile({'*.bmp;*.jpg;*.png;*.tiff;';'*.*'},...
'Select an Image File');

% jika ada file citra yang dipilih maka akan mengeksekusi perintah di
% bawahnya
if ~isequal(file,0)
% membaca file citra yang dipilih
Img = imread(fullfile(path,file));
% melihat ukuran file citra dalam satuan kb
fileinfo = imfinfo(file);
SIZE = fileinfo.FileSize;
Size = SIZE/1024;
% menampilkan ukuran file citra dalam satuan kb
set(handles.edit3,'String',[Size,' kb']);
% menampilkan file citra ke dalam axes
imshow(Img,'Parent', handles.axes1)
% menyimpan variabel Img & fileinfo pada lokasi handles (lokasi
% penyimpanan variabel dalam MATLAB) agar dapat dipanggil oleh
% pushbutton yang lain
handles.Img = Img;
handles.fileinfo = fileinfo;
guidata(hObject, handles)
% mereset button2
axes(handles.axes2)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])
set(handles.pushbutton2,'Enable','on')
set(handles.pushbutton3,'Enable','off')
set(handles.edit1,'String',[])
set(handles.edit2,'String',[])
set(handles.edit4,'String',[])
set(handles.edit5,'String',[])
% jika tidak ada file citra yang dipilih maka akan kembali
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)

% memanggil variabel Img & fileinfo yang ada pada lokasi handles
Img = handles.Img;
fileinfo = handles.fileinfo;

% melakukan lossless kompresi terhadap citra asli
Img_comp = zeros(size(Img));
for n = 1:3
I = Img(:,:,n);
T = dctmtx(8);
B = blkproc(I,[8 8],'P1*x*P2',T,T');
mask = [1   1   1   1   0   0   0   0
1   1   1   0   0   0   0   0
1   1   0   0   0   0   0   0
1   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0
0   0   0   0   0   0   0   0];
B2 = blkproc(B,[8 8],'P1.*x',mask);
Img_comp(:,:,n) = blkproc(B2,[8 8],'P1*x*P2',T',T);
end

% menyimpan file citra hasil kompresi
file_comp = ['Hasil Kompresi.',fileinfo.Format];
imwrite(Img_comp,file_comp);
% melihat ukuran file citra hasil kompresi dalam satuan kb
fileinfo_comp = imfinfo(file_comp);
SIZE = fileinfo_comp.FileSize;
Size = SIZE/1024;
% menampilkan ukuran file citra hasil kompresi dalam satuan kb
set(handles.edit4,'string',[Size,' kb']);
% menampilkan file citra hasil kompresi ke dalam axes
imshow(Img_comp,'Parent',handles.axes2)

% mereset button2
set(handles.pushbutton3,'Enable','on')
set(handles.edit1,'String',[])
set(handles.edit2,'String',[])
set(handles.edit5,'String',[])

% menyimpan variabel Img_comp & fileinfo_comp pada lokasi handles (lokasi
% penyimpanan variabel dalam MATLAB) agar dapat dipanggil oleh
% pushbutton yang lain
handles.Img_comp = Img_comp;
handles.fileinfo_comp = fileinfo_comp;
guidata(hObject, handles)

function edit1_Callback(hObject, eventdata, handles)
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit1 as text
%        str2double(get(hObject,'String')) returns contents of edit1 as a double

% --- Executes during object creation, after setting all properties.
function edit1_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end

function edit2_Callback(hObject, eventdata, handles)
% hObject    handle to edit2 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit2 as text
%        str2double(get(hObject,'String')) returns contents of edit2 as a double

% --- Executes during object creation, after setting all properties.
function edit2_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit2 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
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)

% memanggil variabel Img, fileinfo, Img_comp, dan fileinfo_comp yang ada
% pada lokasi handles
Img = handles.Img;
fileinfo = handles.fileinfo;
Img_comp = handles.Img_comp;
fileinfo_comp = handles.fileinfo_comp;

% menghitung nilai PSNR, MSE, dan % kompresi
nilai_psnr = psnr(Img,Img_comp);
nilai_mse = mse(Img,Img_comp);
filesize = fileinfo.FileSize;
filesize_comp = fileinfo_comp.FileSize;
persen_kompresi = filesize_comp/filesize*100;
% menampilkan nilai PSNR, MSE, dan % kompresi pada edit text
set(handles.edit1,'String',nilai_psnr)
set(handles.edit2,'String',nilai_mse)
set(handles.edit5,'String',persen_kompresi)

% --- Executes on button press in pushbutton4.
function pushbutton4_Callback(hObject, eventdata, handles)
% hObject    handle to pushbutton4 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% mereset button2
axes(handles.axes1)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])
axes(handles.axes2)
cla reset
set(gca,'XTick',[])
set(gca,'YTick',[])
set(handles.pushbutton2,'Enable','off')
set(handles.pushbutton3,'Enable','off')
set(handles.edit1,'String',[])
set(handles.edit2,'String',[])
set(handles.edit3,'String',[])
set(handles.edit4,'String',[])
set(handles.edit5,'String',[])

function edit5_Callback(hObject, eventdata, handles)
% hObject    handle to edit5 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hints: get(hObject,'String') returns contents of edit5 as text
%        str2double(get(hObject,'String')) returns contents of edit5 as a double

% --- Executes during object creation, after setting all properties.
function edit5_CreateFcn(hObject, eventdata, handles)
% hObject    handle to edit5 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called

% Hint: edit controls usually have a white background on Windows.
%       See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end

Pemrograman citra digital di atas merupakan salah satu contoh penerapan metode kompresi lossless dengan meminimalisir data informasi citra yang hilang.

File source code lengkap beserta citra pada materi di atas dapat diperoleh melalui halaman berikut ini: Source Code