There are three main principles of autofocus camera modules: point spread function principle, distance measurement principle, and phase detection principle.
Point spread function principle: This principle determines the focus position by observing the contrast of the edges of the lines in the picture. When the contrast is the highest, it means that the light is completely converged, that is, in focus. This method determines the focus position by detecting the contrast or energy size, but the disadvantage is that when the focus moves back and forth, it is difficult to accurately judge the low-contrast area.
Distance measurement principle: The distance measurement principle determines the focus position by measuring the distance between the camera and the subject. Early methods include trigonometric macular distance measurement and laser distance measurement. This method focuses by determining the distance, but the distance measurement range is limited.
Phase detection principle: The phase detection principle determines the focus position by analyzing the different ways in which the picture blurs when it is out of focus. The phase detection system can directly distinguish whether the focus is in front or in the back, so as to move the focal plane to the correct position in one step, which is currently the most mainstream focusing method.
