The past year has seen the term "pixel binning" regularly pop up when talking about smartphone photography. The term doesn't exactly conjure up excitement, but it's a feature powering loads of phones today.
So what is pixel binning then? Join us as we take a look at one of the leading smartphone photography features on the market.
The importance of pixels or photo sites
To understand pixel binning, we have to understand what a pixel actually is in this context. The pixels in question are also known as photo sites, and they're physical elements on a camera sensor that capture light during photography.
Pixel size is usually measured in microns (a millionth of a meter), with anything at or below one micron considered small. The iPhone XS Max, Google Pixel 3, and Galaxy S10 cameras all offer large 1.4 micron pixels.
Needless to say, you always want your pixels to be large, as a larger pixel can simply capture more light than a smaller pixel. The ability to capture more light means better performance in the pub or at dusk, when light is at a premium. But smartphone camera sensors have to be small in order to fit into today's svelte frames — unless you don't mind a camera bump.
The small smartphone sensor size means the pixels also have to be small, unless you simply use fewer pixels (i.e. a lower resolution sensor). The other approach is to use more pixels (i.e. a higher resolution sensor) but you'll either have to increase the size of the sensor and deal with a bump or shrink the pixels even more. Shrinking the pixels down even more will have an adverse effect on low-light capabilities. But that's where pixel binning can make a difference.
The pixel-binning approach
A 12MP pixel-binned shot taken with the 48MP-toting Honor View 20.
To sum it up in one sentence, pixel-binning is a process that sees data from four pixels combined into one. So a camera sensor with tiny 0.9 micron pixels will produce results equivalent to 1.8 micron pixels when taking a pixel-binned shot.
As we said in our 48MP camera explainer, think of the camera sensor as a yard and the pixels/photosites as buckets collecting rain in the yard. You can either place loads of small buckets in the yard, or several big buckets instead. But pixel-binning is essentially the equivalent of combining all the small buckets into one gigantic bucket when needed.
Read: Honor View 20 camera review — A very high score, and for good reason
The biggest downside of this technique is that your resolution is effectively divided by four when taking a pixel-binned shot. So that means a binned shot on a 48MP camera is actually 12MP, while a binned shot on a 16MP camera is only four megapixels.
Pixel binning is generally made possible thanks to the use of a quad bayer filter on camera sensors. A bayer filter is a color filter used in all digital camera sensors, sitting atop the pixels/photo sites and capturing an image with red, green and blue colors.
Your standard bayer filter is made up of 50 percent green filters, 25 percent red filters, and 25 percent blue filters. According to photography resource Cambridge in Color, this arrangement is meant to imitate the human eye, which is sensitive to green light. Once this image is captured, it's interpolated and processed to produce a final, full color image.
But a quad bayer filter groups these colors in clusters of four, then uses software-based array conversion processing to enable pixel binning. The cluster arrangement delivers extra light information during the array conversion process, making it better than simply interpolating/upscaling to 48MP. Check out the image above for a look at how the quad-bayer filter works — notice how the grouping of the various colors differs from the traditional bayer filter? You'll also notice that it still manages to offer 50 percent green filters, 25 percent red filters, and 25 percent blue filters.
By adopting a quad bayer filter and pixel-binning, you get the advantage of super high-resolution shots during the day and lower resolution, pixel-binned shots at night. And these night-time pictures should be brighter and offer reduced noise over the full-resolution snap.
Who is using pixel binning right now?
If a manufacturer has a phone with a 32MP or 48MP camera, then it's almost guaranteed to offer this feature. Prominent devices in this regard include the Xiaomi Redmi Note 7 series, Xiaomi Mi 9, Honor View 20, Huawei Nova 4, Vivo V15 Pro, and the ZTE Blade V10.
But we also see brands with lower resolution cameras offering pixel binning options, such as LG's G7 ThinQ and V30s ThinQ. These devices offer a Super Bright mode on their 16MP cameras, using pixel binning to give us brighter, 4MP shots. We've even seen brands like Xiaomi adopt 16MP and 20MP cameras with pixel binning, such as the Xiaomi Redmi S2 and Mi A2 respectively.
Clearly higher resolution cameras seem more suitable for the technique (especially on rear-facing cameras), as the output resolution isn't low. But it also makes you wonder how high can you go. Well, a new interview suggests that 64MP and 100MP+ cameras are in the works.
Diminishing returns?
A Qualcomm executive told MySmartPrice brands will launch 64MP and 100MP+ smartphones later this year. This could leave us with 16MP and at least 25MP pixel-binned shots respectively. But unless these ultra high resolution cameras have massive sensors for all those pixels (while still keeping pixels at a comparable size to 48MP sensors), we might be in for a disappointment.
After all, if we've got a 64MP camera with super-tiny 0.5 micron pixels, then a pixel-binned shot would effectively be the equivalent of a 16MP one micron pixel image. So a manufacturer would be going through all that effort to get results that are similar to the OnePlus 6T's selfie camera or the LG G7's primary camera. Why not just adopt a 12MP sensor akin to the Google Pixel or Samsung Galaxy S10 series?
One possibility is that these ultra high resolution cameras could combine data from even more pixels in order to boost low-light performance. But it's unclear whether this is possible just yet via pixel binning. Nevertheless, the Nokia 808 PureView used a so-called oversampling method to combine data from as many as 14 pixels for a cleaner 3MP shot. And if 3MP is too low-resolution for your liking, then the camera was also capable of combining data from eight pixels for a better 5MP snap (or data from five pixels for an 8MP shot).
Even if ultra high resolution cameras don't come to fruition any time soon, the current crop of 40MP and 48MP sensors are already showing impressive results when using pixel binning. With ever-improving capabilities like night modes, better zoom, and AI smarts, there is plenty of potential for better smartphone photos right now.
NEXT: Huawei Mate 20 X review — Android gaming, super-sized
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