Question

Develop a program that magnifies (monochrome) image by a factor of 2^N using bilinear interpolation. Implement this up-scaling in 2 different ways: 1) directly, i.e. calling interp2 once; and 2) ? times iteratively doubling the size. Compare the outputs and discuss the variation in the output (if any).

Answer 1

Answer:

Program using interp2 to upscale the image

clear all

% read the image and convert to 2D array

image1=rgb2gray(imread('CuteFace.png'));

% display the image

figure

imshow(image1)

% convert to double values

image1=double(image1);

% get the size of the image1

[m n]= size(image1);

% define the meshgrid

[x,y] = meshgrid(1:n, 1:m);

% define the scaling factor

upScalingFactor = 2;

% define the meshgrid with the scaling factor

[p,q]=meshgrid(1:upScalingFactor:n, 1:upScalingFactor:m);

% user the interp2 to get the upscaling factor

image2=interp2(x,y,image1,p,q,'linear');

% plot the image

figure

subplot(1,2,1), imagesc(image1), axis, image

title('Original image','FontSize',18)

% plot the upscaled image

subplot(1,2,2), imagesc(image2), axis, image

title('Bilinear interpolation','FontSize',18)

% conver the image

i3 = cast(image2, class(image2));

% store the image

imwrite(i3,'gray1.png');

% display the new image

figure

imshow('gray1.png')

Program to upscale the image using iteration:

% Import my original picture file

N = 2;

image1 = imread('tiger.jpg');

% convert the image to monochrome

image1 = rgb2gray(image1);

% get the dimensions of the image1

[rows columns] = size(image1);

% define the scaling factor

factor = 2 ^ N;

row_new = rows * factor;

column_new = k * factor;

% define the scaling for the new image

x_scale = row_new./(rows - 1);

y_scale = column_new./(columns - 1);

% define the array for the new image

newZoomImage = zeros(row_new, column_new);

% create the output image by using bilinear interpolation

for count1 = 0 : row_new - 1

    for count2 = 0 : column_new - 1

        newZoomImage(count1+1,count2+1) = image1(1+round(count1./x_scale),1+round(count2./y_scale));

    end

end

% plot the images

subplot(1,2,1);

imagesc(image1);

colormap gray;

subplot(1,2,2);

imagesc(newZoomImage);

colormap gray;

% Write the images to files

imwrite(image1,gray(256),'original.jpg');

imwrite(newZoomImage,gray(256),'newZoom.jpg');

In both the programs,

• The first one using interp2, the image size remains same but the internal pixel where refactorized. So that the image is zoomed to detail.
• The second program, due to iteration process, the size of the image is resized to 2^N factor and size of the image increases.

But at final, the images are up scaled to the given factor size.