Image mosaic-ing in Matlab - image

Question

I am trying to do some image analysis over tiles of a big tif image. I have already done the processing required in each of these tiles and in this step I have to create one mosaic out of these tifs. I read somewhere that I can use 'cat' function for this reason. As I am not really pro in programming I found it easy and tried to apply it. The tiles I have are about 154 tifs and I tried the cat over 4 of them and it works and now I should expand it over all the files. My problem now is to apply it over all the tifs. The codes for 4 of them was:
img1 = imread ('E:...\'a1.tif','tif');
img2 = imread ('E:...\'a2.tif','tif');
img3 = imread ('E:...\'a3.tif','tif');
img4 = imread ('E:...\'a4.tif','tif');
image1 = cat(2,img1,img3);
image2 = cat(2,img2,img4);
image3 = cat(1,image2,image1);
imshow(image3)
as you see in the code two by two should be stitch horizontally and the result would be stitch vertically to have the final image. M question is how through these amount of images I define which ones should be stitch first horizontally and then the resulted images stitch vertically. I would be really thankful if you guys could help me with it. Any other approaches would be welcome.

Answer 1

If tiles are of the same size you could concatenate them by operating on them as if they were plain matrices:
% dots-and-linebreak used for prettier formatting
concatenated_image = [ img1, img3; ...
img2, img4 ];
All tiles till ; are concatenated horizontally in one row, and rows are concatenated vertically to form final image.
Applying this principle you could join any number of preloaded images by doing this:
NUMBER_OF_IMAGES = 152; % divisible by 4
IMAGES_PER_LINE = 4;
concatenated_image = [];
for ii = 0 : (NUMBER_OF_IMAGES/IMAGES_PER_LINE)-1
one_row = [];
for jj = 1 : IMAGES_PER_LINE
% concatenate next image in this line
one_row = [ one_row eval(['img' num2str(4*ii+jj)]) ];
end
% add constructed row to the existing image
concatenated_image = [ concatenated_image; one_row ];
end
Instead of using variables named like imgN you should prefer using Matlab's cell arrays. You could then load all the images with:
imgs = {};
for ii = 1:154
imgs{ii} = imread (['E:...\a' num2str(ii) '.tif'],'tif');
end
Then you would have to change the above concatenation code to:
...
one_row = [ one_row imgs{4*ii+jj} ];
...