I was just learning about the frequency domain in images.
I can understand the frequency spectrum in case of waves. It denotes what frequencies are present in a wave. If we draw the frequency spectrum of $\cos(2\pi f t)$, we get an impulse signal at $-f$ and $+f$. And we can use corresponding filters to extract particular information.
But what does frequency spectrum means in case of images? When we take the FFT of a image in OpenCV, we get a weird picture. What does this image denote? And what is its application?
I read some books, but they give a lot of mathematical equations rather than the physical implication. So can anyone provide a simple explanation of the frequency domain in images with a simple application of it in image processing?