Roundness is defined as the degree that the cross section of an object is close to a theoretical circle.In the cigarette production process,the quality and production efficiency of a cigarette are directly affected by the roundness of the un-cut cigarette.To improve the current measurement method using a charge-coupled device (CCD) sensor and measure the roundness of cigarettes in the production line,a visual detection system composed of an industrial camera and a structural light is developed.The system’s roundness-calculation method is closer to the real environment of the cigarette roundness.In this visual system,the line-structure light shines on the cigarette with a fixed angle and height in a longitudinal section,forming a crescent-shaped spot when the industrial camera cannot capture the cigarette’s end surface.Then,the spot is analyzed using image-processing techniques,such as a median filter and ellipse fitting,after the industrial camera captures the spot.The system with a non-contact measurement style can meet the requirements of on-line cigarette detection with stable results and high precision.