What is All Pixel autofocus?
On the Oppo Find X2, Oppo will use All Pixel Omni-Directional Phase Detection Autofocus on a custom sensor developed with Sony. But what does “All Pixel” autofocus actually mean? And how does it relate to existing Dual Pixel and Quad Pixel Phase Detect Autofocus (PDAF) systems?
Focus Pixel is an Apple marketing term for the company’s baseline PDAF approach, first introduced in the iPhone 6 in 2014. A Focus Pixel is simply a PDAF pixel on an image sensor.
Although faster than Contrast Detect Autofocus, this generation of PDAF pixels are used for focusing, not imaging. This means they need to be spread out across a sensor’s surface. With this arrangement, focus pixels might comprise as little as 5% of the sensor area. This equates to slower and less reliable autofocus.
Canon first introduced Dual Pixel PDAF on cameras in 2013. Samsung was the first to use it on smartphones with the Galaxy S7 and S7 Edge back in 2016. Each Dual Pixel PDAF pixel is split into two light-sensitive photodiodes, each with their own microlens or “on-chip lens” (OCL).
With Dual Pixel PDAF, 100% of the pixels on an image sensor are used for both autofocus and imaging. This arrangement greatly improves the focusing performance of a smartphone sensor in terms of speed and reliability.
Quad Pixel PDAF is undeniably great, but it does have limitations. Because of the way the photosite is split, Dual Pixel PDAF can struggle to focus accurately on horizontal lines. This is because the orientation of the split makes them less sensitive to objects that lack pattern change in a horizontal direction.
A Quad Pixel setup aims to solve that issue, by splitting a pixel into four. Each pixel in a Quad Pixel PDAF system is able to analyze left/right as well as top/bottom. This alleviates the issue with horizontal autofocus and is even more reliable and accurate than Dual Pixel PDAF.
All Pixel Omni-Directional PDAF is Oppo’s nomenclature for the autofocus afforded by Sony’s 2×2 OCL sensor. 2×2 OCL is essentially a Quad Pixel Quad Bayer setup with one condenser lens per pixel, covering all four photodiodes. Once again, 100% of an image sensor’s pixels are in use for both focusing and imaging.
The sensor in the upcoming Oppo Find X2 will be larger than normal. This is presumably to accommodate the quad pixel split without lowering sensor resolution or light-gathering capabilities. So All Pixel autofocus will not only be faster than current PDAF methods, it will also provide improved low-light focusing performance.
There are other benefits of the Sony 2×2 OCL solution beyond improved autofocus in all lighting situations and better autofocus irrespective of object shape and pattern. The Quad Bayer structure also means the sensor has higher sensitivity and can reduce noise in low light images and video.
According to Sony, real-time HDR output is possible through a “unique exposure control technology and signal processing function.” Sony also notes that the design and production technology of the 2×2 OCL increases the efficiency of light utilization.
The Qualcomm Snapdragon 865 will also enable a number of other camera features in the Oppo Find X2, so we’ll have to see exactly what Oppo decides to add once it launches.
We’re looking forward to getting our hands on the new sensor early in 2020. Stay tuned for our full Oppo Find X2 review where we’ll be able to fully dissect the performance improvements All Pixel autofocus provides.