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What is pixel binning? Everything to know about this photographic technique

Everyone from Samsung to Xiaomi has been using pixel binning, but what is it? We've got the full rundown for you.
By
November 19, 2021
Oppo Find X3 Pro camera profile
Eric Zeman / Android Authority
Oppo Find X3 Pro

The past few years 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? Join us as we take a look at one of the more popular 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 to be small. For example, the Samsung Galaxy S21 main camera has 1.8-micron pixels, the Xiaomi Mi 11 Ultra has 1.4-micron pixels, and the OnePlus 9 has 1.12-micron pixels.

You generally 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 image quality 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 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

Pixel 6 bridge photo at night 1
Jimmy Westenberg / Android Authority
A pixel-binned 1X shot taken with the Pixel 6.

To sum it up in one sentence, pixel-binning is a photography process that sees data from four pixels combined into one. So a camera sensor with tiny 0.9-micron pixels will produce results comparable to a camera with 1.8-micron pixels when taking a pixel-binned shot.

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. Pixel-binning is essentially the equivalent of combining all the small buckets into one gigantic bucket when needed.

Read: Opinion — Here’s why a 12MP camera phone is more than enough

The biggest downside of this technique is 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, a 64MP camera takes 16MP binned snaps, and 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.

A quad bayer filter used in smartphones with pixel binning

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 or 64MP.

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 it still manages to offer 50% green filters, 25% red filters, and 25% 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. These binned night-time pictures should be brighter and offer reduced noise over the full-resolution snap.

Pixel binning is a way for manufacturers to offer loads of megapixels without adversely affecting low-light performance too much.

In the last year or two, we’ve also seen the emergence of nine-in-one pixel binning (dubbed nona-binning) on some 108MP camera sensors. This is very similar to four-in-one binning outlined above, but combines data from nine adjacent pixels into one. So a 108MP camera with 0.8-micron pixels can deliver images comparable to a camera with 2.4-micron pixels.

As is the case with four-in-one pixel binning, nine-in-one pixel binning also results in the final image being way below the sensor’s native resolution. But where four-in-one pixel binning sees the output resolution being divided by four (so a 48MP camera produces 12MP shots), a nona-binned shot  with a 108MP camera results in 12MP pictures.

Another downside to pixel-binning, in general, is that the color resolution (and therefore color accuracy) will theoretically suffer. So mosaic algorithms have to fill in these color accuracy gaps to ensure accurate results for the final image.

Who is using pixel binning right now?

Realme 8 vs Redmi Note 10 focus on cameras
Dhruv Bhutani / Android Authority

If a manufacturer has a phone with a 32MP, 40MP, 48MP, 50MP, 64MP, or 108MP rear camera, then it’s almost guaranteed to offer this feature. Prominent devices in this regard include the Xiaomi Mi 11, Redmi Note 10, Google Pixel 6 duo, Samsung Galaxy S21 Ultra, OnePlus Nord CE, and Samsung Galaxy A32.

We’ve also seen lots of brands adopt pixel-binning on their selfie cameras, using 20MP, 24MP, 32MP, and even 44MP sensors on the front, and letting users switch between pixel-binned and full-resolution modes.

In the past, we saw phones like the LG V30s even tout four-in-one pixel binning for the 16MP rear camera, promising brighter night shots as a result. But this means you’re left with a 4MP final shot, resulting in a huge drop in resolvable detail. Clearly higher resolution cameras are more suitable for pixel binning (especially on rear-facing cameras), as the output resolution isn’t low.

Diminishing returns?

One question we have on our minds is when does it become a case of diminishing returns? That is, how small can a camera sensor’s pixels go and how many megapixels can be crammed into a tiny smartphone sensor before pixel-binning doesn’t make a difference?

Well, we might find out in the near future as Samsung announced the 200MP HP1 smartphone camera sensor earlier this year. The new camera sensor offers a 1/1.22-inch size that’s actually slightly smaller than the 50MP GN2 camera sensor seen on the Xiaomi Mi 11 Ultra.

This sensor size also means you’ve got small pixels, measuring in at 0.64-microns. That’s very tiny, but Samsung says its 200MP sensor is capable of two types of pixel binning. It can either do four-in-one binning to deliver a shot comparable to a 50MP 1.28-micron pixel camera, or it can do 16-in-one binning to churn out an image equivalent to a 12.5MP 2.56-micron pixel camera.

Samsung has shown nine-in-one pixel binning can work on its 108MP phones, still delivering detailed low-light images that take the fight to rival phones. But the firm’s 108MP phones all have the same pixel size (and therefore similar light sensitivity in theory) as mainstream 48MP and 64MP sensors. So it could have a major challenge on its hands to ensure its first 200MP camera sensor, with those significantly smaller pixels, can deliver the goods when the sun goes down.

Even if 200MP+ camera sensors don’t actually see much, if any, adoption, today’s 48MP, 50MP, and 108MP cameras already deliver impressive image quality when pixel binning. When we combine this with ever-improving image processing smarts, better ultra-wide cameras, more polished zoom, and better silicon, the future of smartphone photography is still looking really good.