How to do the subpixel shift for of an original image multiple times with different values for each time.

Doubt: How to do the subpixel shift for of an original image multiple times with different values for each time.

Background: Lets say i have a gray image of 256x256 (called LR image), and i want to create a super-resolution of this LR image to 512x512 (called HR image). As, in most of the super resolution algorithm, we try to generate multiple LR image with multiple xshift and yshift values which happens to be the subpixel values (<1). Now using these multiple LRs, we try to get the HR using some kind of interpolation methods.

I am looking to do the xshift and yshift, say (0.5, 0.25) of an original image to generate first LR image. Once i get this, i can create multiple such shifts with different values of xshift and yshift.

[Helal Uddin Mullah]

1. Take Fourier Transform of 256x256 image provided.

I=imread('256x256 input image');

LR1=I; [m1,n1]=size(I);

H=fft2(I);

2. x1=0.5;y1=0.25; u=0:1:255; v=0:1:255;

H1=H.*exp(-1i*2*pi.*(u*x1+v*y1)./(m1*n1));

LR2=real(ifft2(H1));

[Matt J]

Fourier transforms are an expensive way to do image shifts. An image shift should be O(N), whereas with FFTs, it will be O(NlogN).

Answer 1

[Matt J]

You can use IMTRANSFORM to make subpixel shifts of an image.

Answer 2

[Image Analyst]

First I'd use imresize to go from 256 to 512. Then I'd use interp2 or griddedInterpolant to interpolate the interpixel values. imtransform will probably also work.