Camera module—PDAF introduction
January 6, 2024
Laser AF (Laser Auto Focus, laser focus)
It senses the distance of an object by emitting infrared rays, and pre-calibrates the mapping relationship between a set of distances and Focus Distance based on the distance. Advantages and Disadvantages: Largely affected by environmental factors and high cost.
CDAF (Contrast Detection Auto Focus, contrast focus)
Take a small part of the picture as a basis for judgment to determine the contrast (sharpness) of the image, that is, the difference between black and white information. When the camera is out of focus, everything looks like a blur, which reduces contrast. CDAF mainly determines focus by detecting the location of the highest contrast during the adjustment process of the contrast information of the focused subject in the image. Advantages and Disadvantages: It requires repeated searches to find the highest contrast value, slow focusing, and high focusing accuracy.
PDAF (Phase Difference Auto Focus, phase focus).
PDAF reserves PDAF pixels on the photosensitive element specifically for phase detection. The focus offset value is calculated through the phase difference to achieve accurate focus.
Advantages and Disadvantages: No need for repeated movement of the lens, fast focusing speed, poor effect in darker environments, and deviation in focusing accuracy
How PDAF works
The working principle of phase focusing is somewhat similar to the human eyes, measuring distance and calculating angle through two independent points. If we can distinguish light coming from different directions and image each. Then at the same time, we can always get two pictures, one picture is imaged by the light from the left, and the other is imaged by the light from the right.