how to get more accurate point position in an image

Question

usually, we can get point position in an image in this way:

figure, imshow rice.png;
[x,y,~] = ginput(1)

what returned is something like this:

x = 121
y = 100

these numbers are measured by pixels, but I'd like more accurate results like:

x = 121.35
y = 100.87

any help would be appreicated!!!

Answer 1

For aligning / registering two images using control points you do need sub-pixel accuracy for the different control points.
Matlab has a very nice user interface for this purpose you might want to look at: cpselect .
A nice tutorial is also available here .

Given two images oim1 and oim2 you may use cpselect to transform oim2 to "fit" oim1 :

>> [input_points, base_points] = cpselect(oim2, oim1, 'Wait', true);
>> T = cp2tform( input_points, base_points, 'similarity' ); % find similarity transformation
>> aim2 = tformarray( oim2, T, makeresampler('cubic','fill'), [2 1], [2 1], size(oim1(:,:,1)'), [], 0 );

Answer 2

I think imagesc can be useful

% load example image    
Istruct = load('gatlin');    
I = Istruct.X./max(Istruct.X(:));

% display it
figure;
imagesc(I);
colormap(gray);

% get some point
[x,y]=ginput(1);

[x, y] % x and y will be double