A blank pistol was fired during the robbery at the Co-op in Butcher Hill, West Park, at about 10.20pm on Saturday, March 26.
A man armed with what appeared to be a handgun approached the lone female member of staff and demanded cash before firing the gun towards the floor.
In fear, the woman handed over cash from the till and the robber ran off towards fields on Spen Lane.
He was described as white, about 6ft to 6ft 3ins tall, aged about 40 with dark eyebrows. He was wearing dark clothing and a black woolly hat and had the lower part of his face covered.
Detective Constable Lee Thimm, of Leeds District CID, said: "This was a terrifying experience for the victim who was left very badly shaken. While we now know that the gun used was a blank-firer she was put in genuine fear for her life faced with an armed man who showed he was prepared to fire the weapon.
"We urgently need to identify this man. Although he has his face partially covered on the CCTV image we would ask people to think about the physical description, his clothing and the Asda bag he is carrying and contact us immediately if they think they know who it might be.
"We would also like to hear from anyone who may have seen the man in the area around the time of the robbery."
Anyone with information is asked to contact DC 908 Thimm at Elland Road via 101 quoting crime number 13160131725 or call the independent charity Crimestoppers anonymously on 0800 555 111.