In this embodiment, the line frequency Q for capturing an image of the object may be determined according to the following formula: Q=v*(f1/p1)/H=Vp*(p2/f2)*(f1/p1)*(h/H);
where Vp is the number of pixels on the imaging plane of the first image capturing module that the image of the object passes through per unit time; p2 is the size of a single pixel of the first image capturing module, and the unit of which may be millimeter; f2 is the focal length of the first image capturing module, the unit of which may be millimeters; p1 is the size of a single pixel of the second image capturing module, the unit of which may be millimeters; f1 is the focal length of the second image capturing module, and the unit of which may be millimeters; h is the distance between the first image capturing module and the object, the unit of which can be mm; H is the distance between the second image capturing module and the object, the unit of which can be millimeter; and the character of * indicates multiplication, and the character of/indicates division.
In this embodiment, when the object passes through the first image capturing module, the distance h between the first image capturing module and the object is determined; and when the object passes through the second image capturing module, the distance H between the second image capturing module and the object is determined.