An arrangement of optical measurement

An arrangement of an optical measurement device, which device comprises at least one image source in order to produce consecutive images on a surface of an object, a camera to take pictures of the surface, and a processor unit in order to compare the pictures of the camera with said images, wherein the arrangement comprises of a first area and a second area on the images, the first and second area being illuminated on alternate images in such a way that when the first area is illuminated on the image, the second area is not illuminated, and the second area is illuminated on the subsequent image but the first area not,

• the arrangement further comprising at least one double detector in order to detect the illuminated first area and the illuminated second area, a drive unit in order to trigger at least one camera, the drive unit being arranged to trigger the camera if the double detector indicates that a state of the first area changes and a state of the second area changes.