Combining Stacked Images Size

I am reading in two figures as

I1 = imread('figure1.jpg');
I2 = imread('figure2.jpg');

I am then stacking them as

I3 = [I1;I2];

Saving the image and reading it back in produces a much smaller figure. I would like it to be the same size (see attached image). Is there a better way of doing this stacking?

saveas(I3,'figure3.jpg')
I4 = imread('figure3.jpg');
f=figure;
imshow(I3)
hold on
imshow(I4)
saveas(f,'figure4.jpg')

Answer 1

[Eleanor Betton]

When I load you images figure 1 and 2 are coming in as .Jfif files.

If you use imwrite instead of saveas for when you save I3 then the file size is preserved.

imwrite(I3,'figure3.jpg')

[Image Analyst]

I think you meant

imwrite(I4,'figure3.jpg');