Quad Bayer vs Quad Pixel AF: what they’re, how they work and the way they differ: Digital Pictures Evaluate

The Olympus OM-1’s sensor has 80 million photodiodes, that are used to ship 20MP photographs and across-the-sensor X-type part detection. This typically will get mistakenly described as a Quad Bayer design. That is not the case although, so we’re going to check out how these two totally different programs work, how they differ, and ponder why neither of the ILCs identified to make use of Quad Bayer sensors make that element public.

What’s Quad Bayer?

Sony Semiconductor has developed a expertise known as Quad Bayer, initially promoted to be used in smartphones.

The Quad Bayer design (proper) makes use of an outsized model of the traditional Bayer sample (left). Every coloration patch extends over 4 photodiodes, every of which has its personal microlens in entrance of it. Picture: tailored from Sony Semiconductor illustration

It makes use of a Bayer coloration filter sample, however every coloured patch extends throughout 4 photodiodes, as an alternative of 1. Every photodiode has its personal microlens, so it may be used as a person pixel, if wanted.

This lets you use the sensor in three other ways, relying on whether or not your precedence is low-light efficiency, the flexibility to deal with high-contrast scenes or attempting to extract essentially the most element from the scene:

• In low gentle, the 4 photodiodes behind every coloration patch can have their output mixed (binned), in order that they collectively act as a single, massive pixel with higher noise efficiency. The picture is 1/4 the sensor’s nominal decision.
• In high-contrast scenes, each different row of the sensor might be read-out early, that means it retains highlights that might in any other case be clipped. This spotlight info might be mixed with the midtone and shadow info to provide a 1/4 decision picture with wider dynamic vary than an everyday sensor.
• In excessive decision scenes, an try is made to re-interpret the Quad Bayer knowledge into one thing nearer to Bayer knowledge, to provide a full decision picture. This would possibly not be as detailed as an precise Bayer picture with the identical pixel depend, but it surely nonetheless provides way more element than the opposite two modes, and therefore is extra detailed than the 1/4 decision sensor wanted to match the low gentle mode’s efficiency.

As you may think, the primary purposes of this expertise have been in smartphones, the place it is used to work across the low-light and dynamic vary shortcomings of tiny pixels on small sensors. Samsung has its personal model, branded ‘Tetracell‘ and a 9 photodiode-per-color variant known as ‘Nonacell.’

This three-mode strategy has direct parallels with Fujifilm’s Tremendous CCD EXR system, which first appeared again in 2009. This basically used a doubled (and 1/2 pixel offset) Bayer sample, slightly than a full quadrupled design, so provided much less element in its excessive decision mode, however the precept could be very comparable.

For top-res mode an try is made to ‘remosaic’ the Quad Bayer output into Bayer-like knowledge. This course of is imperfect. It is value noting that Sony describes this as a ‘conceptual’ diagram. The ‘remosaiced’ knowledge won’t have the colour decision of a traditional Bayer sensor with the identical pixel depend. Picture: tailored from Sony Semiconductor diagram

Apparently, there’s proof that Quad Bayer sensors are used within the Panasonic DC-GH5S and Sony’s a7S III. Neither firm acknowledges this, nor exhibits any outward indication of utilizing something aside from the binned (low-light) mode. Nonetheless, the truth that each cameras are very video centered raises the chance that they use the high-contrast, HDR mode to seize further highlights concurrently with the midtone and shadows (an strategy that avoids any timing distinction between the 2 captures, making it preferrred for video).

We approached each firms for touch upon the selection of sensors in these fashions, however neither addressed whether or not the sensors are Quad Bayer*.

What’s Quad Pixel AF?

The OM-1’s Quad Pixel AF system additionally makes use of coloration filters that stretch throughout 4 photodiodes, but it surely makes use of a single, massive microlenses in entrance of every quartet of photodiodes, powering its X-type PDAF system, however that means you’ll be able to’t use the person photodiodes as separate pixels. Picture: OM Digital Options, with translated captions.

This is not what’s occurring within the OM System OM-1, although. Like a Quad Bayer sensor, it is Quad Pixel AF system makes use of a Bayer coloration filter sample the place every coloured patch extends throughout 4 photodiodes, as an alternative of 1. Nonetheless, the OM-1 has massive microlenses that stretch throughout these teams of 4 photodiodes. Because of this they can not be used as separate pixels, as a result of they solely see one quadrant of the scene in entrance of the digicam.

This design has direct parallels with Canon’s Twin Pixel AF system. However as an alternative of getting left- and right-looking 1/2 pixels, the OM-1 has Up/Left-, Up/Proper-, Down/Proper- and Down/Left-looking 1/4 pixels. This implies the digicam can derive X-shaped AF sensitivity, slightly than the solely horizontal AF sensitivity of Canon’s system.

We have been very impressed by the OM-1’s autofocus outcomes, up to now. However the partial view of the scene acquired by every photodiode to provide the AF system its sense of distance means there isn’t any means for OM Digital Options to ‘unlock’ an 80MP sensor mode. As a result of though its filter sample is identical as Quad Bayer, its microlens design means Quad Pixel AF is not the identical factor.

*Panasonic tells us the GH5S’s chip was chosen for its readout pace, efficiency at excessive achieve and the incorporation of twin conversion achieve, it didn’t deal with whether or not it was Quad Bayer.