Fast focusing method and device for multi-spectral imaging

A fast focusing device for multi-spectral imaging, comprising:

• a camera configured to capture images, wherein the camera including an image analysis apparatus installed therein;
• an optical lens configured to adjust an imaging focal length;
• a stepper motor configured to drive the optical lens to rotate, wherein the stepper motor transmittingly connected with the optical lens by a conveyer belt;
• a filter wheel provided with a plurality of optical filters arranged in a circle, wherein an optical axis of the optical lens being perpendicular to a plane where the filter wheel is positioned and being aligned with a center of a plane where the filters are positioned;
• wherein, one of the filters of the filter wheel is rotated to be coaxial with the optical lens and the camera and form a reference channel;
• the stepper motor drives the optical lens to rotate;
• the image analysis apparatus calculates focus measures corresponding to all rotation positions of the stepper motor, and obtains a first distribution curve that represents a change of the focus measure of the reference channel along with the rotation position of the stepper motor;
• the filter wheel is rotated to use the other filters to form imaging channels respectively, at least three rotation positions of the stepper motor are selected for each of the imaging channels, focus measures at the selected rotation positions are matched with the first distribution curve to obtain an offset value between the first distribution curve and a second distribution curve that represents the change of the focus measure of the imaging channel to be focused along with the rotation position of the stepper motor, and a clear focusing position of the imaging channel to be focused is calculated according to the offset value;
• a fine-tuning focusing operation centering on the calculated clear focusing position by using a minimal rotation interval of the stepper motor is performed to obtain a precise clear focusing position.