filter2() returns darker image

Hi everyone. My goal is to interpolate an image using fspecial() and filter2(). Since filter2() uses conv2(), i thought about using it with every RGB component (filtering first R, then G and B )

I get my image bigger but at the same time it is darker. Here is my code:

clear all
close all
clc

foto=imread('david','JPG');     
[filas,columnas,colores]=size(foto);  

                     

                                

k=3;    %columns*k
z=3;    %rows*z

newfilas=filas*z;        %new number of rows
newcolumnas=columnas*k;  %new number of columns

newfoto=zeros(newfilas,newcolumnas,3); %new vector to store new values

fila_aux=1;
columna_aux=1;

for fila=1:z:newfilas                  %I study the rows every z
    for columna=1:k:newcolumnas        %I studi the columns evey k
        %I store my new values in newfoto 

        newfoto(fila,columna,:)=foto(fila_aux,columna_aux,:);
        columna_aux=columna_aux+1;
    end
    fila_aux=fila_aux+1;
    columna_aux=1;    
end

newfoto=newfoto/255;       

% I create R,G and B variables to store the three components of the new photo
R = newfoto(:,:,1); 
G = newfoto(:,:,2); 
B = newfoto(:,:,3);







H = fspecial('average',[z k]);     

%I apply filter2() to R,G and B
YR = filter2(H,R);             
YG = filter2(H,G); 
YB = filter2(H,B);

 Y = YR + YG + YB;  %I concatenate R,G and B to create the new filtered matrix of colors
 
figure;imshow(foto);        %I show the original pic
title('Original');


figure;imshow(Y);           %I show the edited one (IT IS LARGER AS EXPECTED BUT ITS ALSO DARKER)
title('New one (edited)');

Answer 1

[Prabhan Purwar]

Hi,

Following code illustrates the interpolation using filter2 and fspecial

clear 
close all
clc

foto=imread('office_3.jpg'); and 
filter_coef= fspecial('average',[3 3]); 
Y=interp(foto,filter_coef);
imshow(Y);
function Y = interp(A, filter_coef)

if (length(size(A)) == 3)
   for i=1:3
        Y(:,:,i) = interp(A(:,:,i),filter_coef);
    end
    
else
    
    [m,n] = size(A);
    A_ = []; Y = [];
    % columns interpolation
    A_col= filter2(filter_coef,A);
    for i=1:n
        A_ = [A_ A(:,i) A_col(:,i)];
    end
    A_(:,end) = [];
    % rows interpolation
    A_rows = filter2(filter_coef,A_')';
    for i=1:m
        Y = [Y; A_(i,:); A_rows(i,:)];
    end
    Y(end,:) = [];
    
end
end

Output: