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Redmi Note 4

[Discussion] [Device Team] [Tech Class] Chapter 10 : PDAF and its difference with CDAF

2017-02-07 21:15:38
11179 281
Edited by Karthik Mohan at 2017-02-08 07:48 AM

Hello Mi Fans,
Hope you guys are having loads of fun here in our Mi Community.
In today's 'Tech Class' we will take you through PDAF Technology,
Difference between CDAF & PDAF and much more.


PDAF is Phase Detect Auto Focus system. Its a focus system used by DSLRs when shooting through the viewfinder. The advantage of this is faster auto focus, better subject tracking and less focus hunting(useful in videos).If you want to minimize the motion blur when the subject is moving (or you are moving, like inside a vehicle), phase-detect autofocus is useful.
PDAF in a continuously focusing mode is a closed-loop control process. PDAF in a focus-locking mode is widely believed to be a "one measurement, one movement" open loop control process, but focus is confirmed only when the AF sensor sees an in-focus subject. The only apparent differences between the two modes are that a focus-locking mode halts on focus confirmation, and a continuously focusing mode has predictive elements to work with moving targets, which suggests they are the same closed-loop process.

How PDAF Technology helps Cameras to focus fast

The camera has become more and more important in smartphones and people have higher requirements for its focusing speed. A lot of methods to assist focusing are available in the current market, including laser, infrared, and phase focusing. Focusing is the process whereby a motor moves to bring the subject into focus. Focusing algorithms are divided into contrast detection and phase detection auto focus (PDAF). Let us look into detail on how PDAF Technology works.
In contrast focus (traditional auto focus systems), the moment you start your camera app, a lot of calculations are done by the processor to achieve the correct focus. First, the camera software triggers the lens to move and scan through its entire range of possible focus points, then it returns to whichever settings that provides the sharpest focus. Contrast detection requires the motor to move to different positions until the image displayed on the viewfinder shows the highest contrast. Contrast detection achieves precise focusing but takes a long time because the motor has to keep moving to find the highest contrast.
Phase detection is the process whereby the phase difference of the subject at the imaging plane is calculated to determine the distance between the motor’s current position and the position required for bringing the subject into focus. The motor then moves to this position.
Phase detection takes a short time, but the phase difference is easily affected by various factors such as noise. Therefore, phase detection is not suitable for focusing at low luminance, in a flat area, and on parallel patterns.

PDAF Technology uses paired masked pixels on the image sensor that are engineered to work just like your eyes; your left and right eye are separated by a distance, just like these paired pixels.

As shown above, the dark points represent the PD pixels. The phase information read using the PD pixels can be used to determine the corresponding focal length. After the GPU receives the focal length information, it can swiftly drive the lens to move to a position with the optimal focus.PDAF Technology increases the focusing speed using planar image phase detection. This technology was first applied to the Interchangeable Lens Digital Camera, which allows the user to keep taking HD photos of fast-moving objects (children, pets, or cars) using autofocus. Compared to traditional focusing technology, the PDAF focusing speed has been greatly improved.PDAF focusing technology, however, is not applicable to all scenarios because there is a lot of room for error. Therefore, hybrid focusing systems are commonly adopted with phase focusing used to find the correct position and contrast focusing used to achieve the optimal focus.

Difference between CDAF & PDAF

         CDAF focuses directly on the sensor. It uses a distinct lline in the image by moving the lens until that line obtains the highest contrast, which coincides with the sharpest focus. It works best with lenses designed to move with these focus motions.PDAF uses a sensor placed in the light path created by the mirror. It works basically the same way with any DSLR, or single lens reflex camera, like the E-5. It uses two sensor points to detect the phase difference in the light path and find the exact distance. Then it moves the lens once to the correct focus point. Some of the 4/3 lenses tend to pass this point and hunt for focus several times before locking focus. The 50 mm f/2 macro is an example of this. Macro lenses of all types and brands tend to struggle to find focus.
Redmi Note 4 is having PDAF Technology which help us to have some good focus here is a sample from Note 4 without any edits.

Credits: Google Images, Wikipedia, Special Thanks to Device Team Members, our Mentors @fauwaz  & @paramgagan

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2017-02-07 21:15:38
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nice one Sir
2017-02-07 21:18:30


soumyajit_pal | from mobile


Nice information.. Thanxxx
2017-02-07 21:24:55

Pro Bunny

Savinay Sona | from Redmi 3S


nice information
2017-02-07 21:32:55

Pro Bunny

sumit kushwaha | from app


thanks yaar
2017-02-07 21:35:57

Master Bunny

Being Savvy | from Redmi Note 3


Xiaomi cameras Technology is better
2017-02-07 21:37:06

Read Only

1592671301 | from Redmi 3S


thanks for sharing
2017-02-07 21:51:30

Pro Bunny

MPT | from Redmi Note 4


Excellent thread.. Thank you for sharing..
2017-02-07 21:54:12

Master Bunny

Arjun555 | from app


Useful information..
Thanks for sharing Karthik bro..
2017-02-07 22:05:53
Mi Fan

Grandmaster Bunny

Aziz,rahman. | from Redmi Note 3


well explained...!!
very nice info thanks for sharing...!!
2017-02-07 22:35:28
Thanks for the useful share mate !
2017-02-07 22:50:13
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Karthik Mohan

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