Nearest Neighbor Interpolation

This method is the simplest technique that re samples the pixel values present in the input vector or a matrix. In MATLAB, ‘imresize’ function is used to interpolate the images.

Consider the following example,

The pictorial representation depicts that a 3x3 matrix is interpolated to 6x6 matrix. The values in the interpolated matrix are taken from the input matrix (i.e) no new value is added.

MATLAB CODE:

%3x3 Matrix

A = zeros(3,3);

A(:)=[10,2,9,4,18,14,22,7,25];

display(A); %Before Interpolation

C = imresize(C,[6,6],'nearest');

display(C); %After Interpolation

EXPLANATION:

The result as shown in the pictorial representation can be achieved using the MATLAB function ‘imresize’

Now let’s see how to perform nearest neighbor interpolation without using the MATLAB ‘imresize’ function

MATLAB CODE:

%READ AN INPUT IMAGE

A=imread('cameraman.tif');

% DEFINE THE RESAMPLE SIZE

Col = 512;

Row = 512;

%FIND THE RATIO OF THE NEW SIZE BY OLD SIZE

rtR = Row/size(A,1);

rtC = Col/size(A,2);

%OBTAIN THE INTERPOLATED POSITIONS

IR = ceil([1:(size(A,1)*rtR)]./(rtR));

IC = ceil([1:(size(A,2)*rtC)]./(rtC));

%ROW_WISE INTERPOLATION

B = A(:,IR);

%COLUMN-WISE INTERPOLATION

B = B(IC,:);

figure,subplot(121),imshow(A);title('BEFORE INTERPOLATION'); axis([0,512,0,512]);axis on;

subplot(122),imshow(B);title('AFTER INTERPOLATION');  axis([0,512,0,512]);axis on;

MATLAB CODE :

clear all

clc

close all

%READ A RGB IMAGE

A=imread('peppers.png');

% DEFINE THE RESAMPLE SIZE

Col = 256;

Row = 192;

%FIND THE RATIO OF THE NEW SIZE BY OLD SIZE

rtR = Row/size(A,1);

rtC = Col/size(A,2);

%OBTAIN THE INTERPOLATED POSITIONS

IR = ceil([1:(size(A,1)*rtR)]./(rtR));

IC = ceil([1:(size(A,2)*rtC)]./(rtC));

%RED CHANNEL

Temp= A(:,:,1);

%ROW-WISE INTERPOLATION

Red = Temp(IR,:);

%COLUMNWISE INTERPOLATION

Red = Red(:,IC);

%GREEN CHANNEL

Temp= A(:,:,2);

%ROW-WISE INTERPOLATION

Green = Temp(IR,:);

%COLUMNWISE INTERPOLATION

Green = Green(:,IC);

%BLUE CHANNEL

Temp= A(:,:,3);

%ROW-WISE INTERPOLATION

Blue = Temp(IR,:);

%COLUMNWISE INTERPOLATION

Blue = Blue(:,IC);

Output=zeros([Row,Col,3]);

Output(:,:,1)=Red;

Output(:,:,2)=Green;

Output(:,:,3)=Blue;

Output = uint8(Output);

figure,subplot(121),imshow(A);title('BEFORE INTERPOLATION'); axis([0,512,0,384]);axis on;

subplot(122),imshow(Output);title('AFTER INTERPOLATION');  axis([0,512,0,384]);axis on;

EXPLANATION:

For RGB image, the Red, Green and Blue channels are interpolated separately.