2D Fourier Transform of an image to remove grating

[User002]

I'm trying to remove a grating that has been added to my image:

My plan is to perform a 2D Fourier transform of the image. The grating will come up as a block signal, so that's an infinite series of frequency, growing weaker as it goes to higher and higher components. So I want to block those frequences whilst at the same time preserving my image as much as possible (I know this is kinda contradictory).

Unfortunately, I am failing at the first step: transforming it to the Fourier domain. This is my code:

When I try to run it I get this error.

Anyone have any ideas to fix this?

[Bozhidar]

I found a Knowledge Base that possibly will help you, check the following link: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000001DbuVSAS&l=en-US

One more thing.. I do not see anywhere assigned path to get the image, which in future will throw an error for sure.

Best,

Bozhidar