Crossword Genius

My photo turned out grainier with a mobile imaging technique (10)

Ross

I believe the answer is:

tomography

I'm a little stuck... Click here to teach me more about this clue!

'technique' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

I've seen this clue in The Times.
Want a hint initially instead of a full solution? Install my app