Zoom Images : Nearest Neighbour & Bilinear Interpolation

The method zoom() will get the image name and the zoom factor as arguments and produce the required zoomed image using both Nearest neighbour and Bilinear interpolation methods to help us compare the results.

In nearest neighbour method, I just repeated the rows and columns to get the required zoom level. 

In bilinear interpolation method, first I copied the original pixel values to a new matrix and did the interpolation in two steps. First, I interpolated the columns (in x-direction) using original pixel values. Then, I interpolated the rows (in y-direction) which finished the bilinear interpolation.

Matlab Code

function zoom (name,n)
    close all
    im=imread(name);
    im=rgb2gray(im);
    imshow(im);
    [r,c]=size(im);
    % NEAREST NEIGHBOUR
    x=zeros(r*n,c*n);
    for i=1:r
        for j=1:c
            x(i*n-n+1:i*n,j*n-n+1:j*n)=repmat(im(i,j),n,n);
        end
    end
    figure
    subplot (1 ,2 ,1)
    imshow(mat2gray(x));
    title('Nearest Neighbour');
    % BILINEAR
    im = im2double(im);
    [r,c]=size(im);
    y=zeros(r*n-n+1,c*n-n+1);
    % COPY THE ORIGINAL VALUES
    for i=1:r
        for j=1:c
            y(i*n-n+1,j*n-n+1)=im(i,j);            
        end
    end         
    % INTERPOLATE IN X-DIRECTION
    [row,col]=size(y);
    for i=1:n:row
        for j=1:col
            m=mod(j,n);
            if(m==0)
                m=n;
            end
            if(m~=1)
                y(i,j)=((m-1)*y(i,j-(m-1)+n) + (n-(m-1))*y(i,j-(m-1)))/n;
            end
        end
    end      
    % INTERPOLATE IN Y-DIRECTION
    for i=1:row
        for j=1:col
            m=mod(i,n);
            if(m==0)
                m=n;
            end            
            if(m~=1)
                y(i,j)=((m-1)*y(i-(m-1)+n,j) + (n-(m-1))*y(i-(m-1),j))/n;
            end
        end
    end
    subplot (1 ,2 ,2)
    imshow(y);
    title('Bilinear');
end

Output

You can notice that, bilinear interpolation method gives more smooth output.