Question

i am trying to apply SURF algorithm, which is the algo to find the key points and matches corresponding two images, but the problem is that in my case , i want to apply that algo with two images, but they are of different dimension and so it fails to work, could you please tell what shall i do so that both images become equal dimensions.

Answer 1

That depends on your problem. If the images have the same resolution, I suggest you either crop one image or extend one image (with zeros?) to match the number of pixels.

Otherwise I suggest you interpolate the images so that they are defined at the same points, for example with interp2.

Can you give a minimum working code example of what you are trying to do?

Edit:

The code example you gave starts with loading to images.

% Example 2, Corresponding points
% Load images
I1=imread('TestImages/lena1.png');
I2=imread('TestImages/testc2.png');

Here are a few examples of how you can make the images match. You have to decide which one of these makes sense in your case.

Method 1: crop both images

nrows = min(size(I1,1), size(I2,1));
ncols = min(size(I1,2), size(I2,2));

% The + floor( ... ) is only for centering the bounding box
croppedI1 = I1( (1:nrows) + floor((size(I1,1)-nrows)/2), ...
  (1:ncols)+floor((size(I1,2)-ncols)/2), ...
  :);

croppedI2 = I2( (1:nrows) + floor((size(I2,1)-nrows)/2, ...
  (1:ncols) + floor((size(I2,2)-ncols)/2), ...
  :);

I1=croppedI1;
I2=croppedI2;

Method 2: Extend the images with zeros until they match

nrows = max(size(I1,1), size(I2,1));
ncols = max(size(I1,2), size(I2,2));
nchannels = size(I1,3);

extendedI1 = [ I1, zeros(size(I1,1), ncols-size(I1,2), nchannels); ...
  zeros(nrows-size(I1,1), ncols, nchannels)];

extendedI2 = [ I2, zeros(size(I2,1), ncols-size(I2,2), nchannels); ...
  zeros(nrows-size(I2,1), ncols, nchannels)];

I1=extendedI1;
I2=extendedI2;

Method 3: Scale the second image to the size of the first one (which destroys the aspect ratio)

% Scale the coordinates so that they range from 0 to 1 each.
[X1, Y1]=meshgrid( linspace(0, 1, size(I1,2)), linspace(0, 1, size(I1,1)));
[X2, Y2]=meshgrid( linspace(0, 1, size(I2,2)), linspace(0, 1, size(I2,1)));
nchannels = size(I1,3);

% interpolate each color plane separately
for k=1:nchannels
  scaledI2(:,:,k)=interp2(X2, Y2, double(I2(:,:,k)), X1, Y1); 
end

%I1=I1;
I2=scaledI2;