I am confused with 2d magnitude plot of frequency spectra. So we have 2 images, the first one is shown at the top, and the dilated or enlarged version of the white box is shown at the second row.
For the dilated version, in the spatial domain when travelling in the $x$-direction, you see a fast change in intensity, and when you travel in the $y$ direction, the change is slower, so that the $v$ direction frequency component is smaller. In the frequency domain, $x$ maps to $u$, and $y$ maps to $v$.
I do understand that when you enlarge in one domain, you must do the opposite to the other domain. The thing I don't understand is that in the dilated version, when you travel in $x$, and you still see the same rate of change as in the original image. Since $u$ maps to $x$ in the frequency domain, we expect that the frequency spectrum looks the same in the $u$ direction. However, the result is that, in the $u$ (or the horizontal) direction of frequency domain, its frequency component shrinks; the $v$ direction remains intact. But we just change its $y$ direction!
Update: To be more precise, please refer to the area of the red box. In the second figure, it gets shrink.