The problem has nothing to do with imshow(). It's two things:
- it's basic geometry
- default subplot() behavior wastes tons of space
Regarding #1, you have 100 images, the majority of which are landscape orientation with an AR of about 3/2. You are tiling them 20/5 in a figure with an AR of about 2/1. There will obviously be a huge gap between the rows. There necessarily must be. Either change the tiling or change the figure aspect ratio.
Regarding #2, either you have to manually tweak position properties in order to make subplot() make better use of space, or you have to use something else. You can try using tiledlayout(). It's slower, but it has more options for making good use of space. It's relatively new, so the old version I have is flaky and not all those said options are supported. I can't really craft a fully-complete solution because of that. You'll have to play around with it yourself:
% test images
L = ones(66,100); % landscape AR 3/2
P = ones(100,66); % portrait AR 2/3
imgs = {L P};
% there are 14 portrait images, 100 total
idx = ones(100,1);
idx(1:14) = 2;
idx = idx(randperm(100));
% maybe use a tiling that's closer to square
% extra slots are simply unused
tiledlayout(6,17,'tilespacing','none','padding','none')
for k = 1:100
nexttile
imshow(imgs{idx(k)}*rand(1)*0.5+0.25);
end
Like I said, you'll have to find a figure aspect ratio or a tiling that makes for good density.
Look at tilespacing and padding options:
