The painting machine was a light-sensitive spray-gun. When light fell on the light cell the spray-gun would stop spraying. It only sprayed when there was no light. The light cell was situated at the end of a tube, so it would only react to the light directly hitting straight into the length of the tube. If it encountered a dark point, the spray-would spray; if not, it would shut. The spray was hoisted onto a wooden construction which moved back and forth along the wall. It reacted to the dark and light points in the room and painted them on the wall. It creates a photographic image, in which all perspective is vanished. All the objects in the image are the same size as the real objects.