How do smartphone cameras know when they’re in focus?
Asked 10/3/2017
104 views
2 answers
0
I’m new to cameras and wondering how smartphone autofocus works. I assumed a camera would need to know the distance to the subject in order to focus on it. Is that actually how it works? Do smartphones use depth sensors to measure distance, or do they determine focus some other way?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
3
The vast majority of smartphones that can change the focus distance use contrast detection autofocus.
With contrast detection AF: The focus is moved and the camera compares the amount of contrast on the selected portions of the imaging sensor at the first position to the amount contrast at the second position. It continues to do this until it finds the point at which it moves past greatest contrast and the contrast begins to be reduced by further travel in the same direction. It then returns the focus position to the point of greatest contrast.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
9y ago
0
Generated from our catalog & community — verify before relying on it.
Most smartphones that can adjust focus use contrast-detection autofocus. Instead of directly measuring the subject’s distance, the camera looks at image data from the sensor and moves the lens focus back and forth while checking contrast in the selected area.
When an image is out of focus, edges and details look softer, so contrast is lower. As focus improves, contrast increases. The phone keeps adjusting focus until it finds the point of highest contrast; if contrast starts decreasing, it knows it has gone past the best focus point and moves back.
So, in general, the phone does not need to know the exact distance to the subject to focus. It can determine focus by analyzing the image itself. Depth sensors are not required for this method.
Recommended products
UniqueBot
AI9y ago
Your Answer
Related Questions
How large can you realistically print photos from a 24MP or 40MP smartphone camera?
How do contrast-detect and phase-detect autofocus decide what to focus on?
How do smartphone cameras focus, and why can autofocus be slow or miss focus?
How do you calculate depth of field on a smartphone camera at different focus distances?
How far should a subject stand from a backdrop?