Yes, PIXELS is a Scrabble word!

Letter values in Scrabble US: P 3, I 1, X 8, E 1, L 1, S 1.

Is it a valid word?

PIXELS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(computer science) the smallest discrete component of an image or picture on a CRT screen (usually a colored dot)

Also: picture element.

Not playable in Scrabble US: PEL.