A function that is becoming increasingly popular in smartphone cameras is pixel binning.It has created quite a bit of a stir with some people questioning whether it is even necessary.
In this article, we will look at what pixel binning is, how it works, and how it affects mobile photographs.
What is pixel binning?
Pixel binning is a process that combines multiple pixels that are next to each other on a smartphone camera’s sensor to create one large superpixel. It is designed to reduce noise in digital images by increasing the signal-to-noise ratio and thus improve camera performance, especially in low light conditions.
To fully understand how pixel binning works, you have to first know what pixels are and how they work. I’ll do a brief overview here but I recommend you read more about pixels in this article.
What are pixels?
The surface of a smartphone camera sensor is made up of millions of elements that capture the light that enters the camera to create an image. These elements are known as photosites, a.k.a pixels.
Extreme closeup of the surface of a digital camera sensor. The coloured dots are photosites overlaid with a colour filter array.
One million of these pixels is collectively known as a megapixel. So, a camera that is said to be 12MP (megapixels) means that its sensor has twelve million photosites/pixels on its surface.
Because their function is to capture light information in order to produce an image, the size of each pixel is very important. The bigger the pixels are, the more light can be captured. In turn, the more light the pixels can capture, the better the picture quality.
The size of a pixel is measured in microns (µm). Currently, pixels on smartphone sensors range between 0.8µm and 1.4µm in size. If you compare this to the size of the pixels on a DSLR camera, smartphone cameras trail very far behind.
Is pixel binning necessary?
Smartphone cameras are known to have small sensors. This is why the pixels on these sensors are also small. To give you an idea how small they are, pixels on a full-frame DSLR camera can reach about 8µm. This makes a smartphone camera’s 0.8µm pixels pale in comparison.
The problem with small pixels is their inability to capture a lot of light and their susceptibility to digital noise. This results in pictures that are dark and grainy, especially when the lighting conditions are not ideal.
Pixel binning provides a unique solution for this shortcoming in mobile cameras. By combining the electric current of multiple pixels that are next to each other, the size of the sensor’s pixels will essentially increase.
Pixel size increase due to pixel binning
In other words, a sensor that had 0.8µm pixels will have 1.6µm pixels after 4-to-1 pixel binning. We’ll look into exactly what this means further on.
By increasing the size of the pixels on the sensor, pixel binning makes it possible for the camera to take better quality pictures in low light conditions.
Why not just have larger pixels instead of pixel binning?
The answer is simple-- marketing. For years, consumers have been led to believe that the number of megapixels a camera has is the number one determining factor of picture quality. However, this is not entirely true.
Although megapixels do play a part in image quality, there are a lot of other factors that contribute to that as well.
Unfortunately, the megapixel war has been waging for so long, people have fallen for the hype and believe that more megapixels mean a better smartphone camera. Therefore, smartphone manufacturers play into that belief in order to push the sales of their devices.
Think about it. Which one sounds more extraordinary-- a phone with a 12MP camera or a phone with a 108MP camera? Of course, the 108MP camera phone is likelier to create more buzz.
That’s the case with the Samsung Galaxy S20 Ultra, for example. By default, the primary rear camera of the S20 Ultra takes 12MP photos with 2.4µm pixels. But because most consumers don’t understand the importance of the size of the pixels and the impact of sensor size on mobile photos (and other mobile camera specs), the hype is around the 108MP sensor.
However, there is an upside to pixel binning instead of just having large pixels. If the lighting conditions are ideal, you have the option of switching to a higher resolution for your shots. Although this is not necessary for sharing images on social media, it can make a difference if you want to print your photos.
The bigger you want to print your mobile photos, the more resolution you need. Trying to blow up a low-resolution image will result in a poor-quality photo that’s pixelated.
If you have photos, drawings, or images that you want to turn into works of art for your home or to give as a gift, I recommend you check out Pictorem. They can print your photos on canvas, metal, wood, acrylic, and more.
They’ve been around for years and offer top-quality products at unbeatable prices. Their service is amazing and I honestly couldn’t be happier with their prints. They look great on any wall.
How does pixel binning work in smartphone cameras?
One does not simply understand how pixel binning works on smartphone cameras without knowing how the image sensor works to begin with. To avoid making this post unnecessarily long, I’ll just cover the basics of it briefly. If you want to learn more about smartphone camera sensors, click here.
As previously mentioned, the surface of an image sensor is made up of millions of photosites (pixels). But that’s not all. Above these millions of photosites is a thin layer known as a colour filter array or CFA, as illustrated below.
Illustration of a Bayer filter on the sensor
This filter is what makes it possible for cameras to capture colour images because any sensor on its own only “sees the world” in monochrome.
Bayer filter array
The most common CFA found on most smartphone camera sensors is the Bayer filter. This colour filter array covers 50% of the photosites on the sensor with a green filter, 25% with a red filter, and the remaining 25% with a blue filter.
How a Bayer filter works
Each photosite on the sensor will only absorb the light that matches its filter and reflect the rest. For example, a photosite with a green filter will only absorb green light.
On a standard Bayer filter, these colour filters are scattered across the sensor in a checkered fashion, one after the other. A section of four neighbouring photosites on a sensor will have RGGB (red, green, green, blue) filters, as illustrated below.
If the four RGGB (red, green, green, blue) pixels illustrated above were to be merged into one pixel, say red, for example, then those pixels will no longer be four individual RGGB pixels but rather just one R pixel.
The next four pixels next to the R superpixel will either be a group of four merged G pixels or a superpixel made up of four blue pixels.
This merging of pixels in groups of four is made possible by a version of the Bayer filter known as the Quad-Bayer filter. By combining the electronic charge of four pixels into one (known as 4:1 or 4-to-1 binning), the Quad-Bayer filter essentially doubles the size of the pixels.
2x2 binning simply means that an area of 2 pixels high and 2 pixels wide is combined. What was once a 0.8µm pixel can become a 1.6µm superpixel.
Where 2x2 binning combines four pixels into one, 3x3 binning merges an area of 3 pixels high and 3 pixels wide into a superpixel. Essentially, nine pixels become one. A blue pixel that was 0.8µm is multiplied by three and becomes 2.4µm big. That’s a significant increase for a smartphone camera.
At the time of this writing, not many phones use 3x3 (9-to-1) binning. But because it’s sensor is so large and has so many megapixels, Samsung was able to introduce 3x3 pixel binning to their flagship Galaxy S20 Ultra.
Similarly, the Xiaomi Mi Note 10 Pro also has a 108MP sensor, also made by Samsung. But unlike the Galaxy S20 Ultra, the Mi Note 10 Pro uses a Quad-Bayer filter that supports 2x2 pixel binning and not 3x3 pixel binning.
Although there are dedicated cameras that merge up to 16 pixels into one superpixel, no smartphone currently on the market does that. And for good reason.
Sure, a 0.8µm pixel can increase in size to an impressive 3.2µm that begins to rival that of bigger cameras but this may have a negative impact on how the photo turns out, given how small smartphone sensors are. Let’s have a quick look at how.
How does smartphone pixel binning affect mobile photos?
Pixel binning affects two major aspects of smartphone photos-- the image quality and the resolution. Unfortunately, to improve on one aspect means you have to sacrifice the other.
The greatest and most desired effect of pixel binning is the improvement in picture quality. As previously mentioned, small pixels are susceptible to digital noise when the lighting conditions are not ideal. That’s one of the reasons why DSLR cameras take better pictures than smartphone cameras-- they have bigger pixels.
Pixels binning allows smartphone cameras sensors to have bigger pixels than they normally would, thus ensuring better performance in low lighting. The resulting images are brighter and have far less digital noise.
The trade-off for better image quality by pixel binning is the resolution of the image.
Because pixel binning essentially merges multiple pixels to create one superpixel, it does have an impact on image resolution. If you have pixel binning enabled on your mobile camera, the resulting images will be lower in resolution compared to if pixel binning was disabled.
How much the resolution decreases depends on the number of pixels that are binned together. A smartphone camera sensor that merges four pixels into one, essentially reduces the resolution by four. So, a 48MP sensor that has 4:1 pixel binning will capture a 12MP image.
Remember how the Samsung Galaxy S20 Ultra and the Xiaomi Mi Note 10 Pro both have the same sensor but use different pixel binning methods? The Mi Note 10 Pro uses 2x2 pixel binning, which reduces the resolution from 108MP to 27MP.
On the other hand, because the Galaxy S20 Ultra uses 3x3 pixel binning, it divides the resolution by 9. So by default, the Galaxy S20 Ultra takes 12MP photos, not 108MP.
Although the resolution is smaller, it’s not necessarily a bad thing. Remember, pixel binning combines small pixels to create bigger pixels in order to capture more light and reduce digital noise. So, the image size will be smaller but the low-light quality will be greater.
Besides, you don’t really need to capture 48MP photos anyway, let alone 108MP. Read the real truth about megapixels here.
Pixel binning and shooting RAW
If you want to capture RAW photos with your smartphone, then you cannot use pixel binning. If the manufacturer allows it, your mobile camera can only output RAW files that aren’t pixel binned or jpeg files that are either pixel-binned or not pixel binned.
In other words, if you want to capture a RAW photo with a 64MP camera that has 0.8µm pixels, you can only do so at that resolution. You cannot take a pixel binned 16MP RAW photo.
And given that RAW images are uncompressed, at 64MP, a RAW image is going to be huge. So, lots of space will be required.
However, if you choose to save your shots as jpegs, you can change the camera’s resolution as you please and not worry too much about the file size because of the conversion and compression the image goes through in the ISP (image signal processor).
The downside is you lose all the benefits of shooting RAW.
Pixel binning vs downsampling
Downsampling is a term that refers to decreasing the number of pixels in an image by scaling it down, thus making the size (resolution) of the picture smaller. This is also referred to as resizing or rescaling.
Although both downsampling and pixel binning result in an image with a reduced resolution, these two things are very different.
Pixel binning is a process that happens on the sensor before the image is taken. Multiple pixels are combined to create one big superpixel that performance better in low lighting. Pixel binned images have a reduced resolution because the pixels are bigger in size.
Downsampling is a process that happens after the image is captured by the sensor. This can either be done in-camera by the phone’s ISP or manually using a photo editing app or computer software.
You can learn more about the differences between pixel binning and downsampling in detail in this article.
When should you use pixel binning?
Most, if not all smartphones that support pixel binning, have it as the default setting. You need to go into the camera’s settings to switch to the highest resolution. To me, this makes perfect sense.
The truth is, you don’t need to shoot at ridiculously high resolutions. It’s best you take advantage of the bigger pixels and take stunning mobile photos, particularly when the lighting is poor. This could be at night or even during the day in areas that don’t receive enough light.
As mentioned previously, if you want to print large prints of your mobile photos, then by all means, go ahead and shoot at full resolution. Outdoor mobile photos in the sun usually turn out better because of the abundance of natural light for mobile photography.
However, you can still shoot at high resolutions on your smartphone indoors or at night, provided there is adequate lighting that you can find or set up.
Which smartphones support pixel binning?
If a smartphone is said to have a very high megapixel count (ie. 30MP or more), chances are it supports pixel binning. In fact, I believe you’d have a tougher time finding a mobile camera high up on the megapixel scale that doesn’t use pixel binning than you would one that doesn’t.
The truth is 0.8µm pixels are too small to capture great mobile photos in poor lighting. Most, if not all popular smartphones that have cameras with 0.8µm pixels, use pixel binning by default in order to capitalise on the increased pixel size.
However, it’s not just smartphones with highest megapixel counts that use pixel binning. Few mobile cameras on the lower end of the megapixel spectrum also use pixel binning.
This is not so popular because a 16MP that pixel bins down to 4MP does not sound so appealing and probably wouldn’t sell so well as a primary camera in today’s smartphone market that’s obsessed with mobile camera specs.
Enabling and disabling pixel binning on a smartphone camera
By default, smartphones that support pixel binning already have it enabled. To take a photo at full resolution using a high-megapixel mobile camera, you’ll need to go to the settings of the camera app to switch to the resolution you want.
Do phones with pixel binning take better photos?
The main aim of pixel binning is to improve the quality of mobile photos by increasing the size of the pixels. But that doesn’t mean that your phone is doomed to take terrible photos because it doesn’t pixel bin.
Remember, a lot of recent phones that use pixel binning have small pixels at full resolution. By default, they take picures with larger pixels at a reduced resolution. This is virtually no different from shooting with a smartphone camera that naturally has large pixels and doesn’t use pixel binning.
For example, the Apple iPhone X has 16 million 1.4µm pixels and doesn’t use pixel binning, whereas the Huawei Nova 7 has 64 million 0.8µm pixels at full resolution. When pixel binned, as per default, the Nova 7 sports a 16MP camera with 16 million 1.6µm pixels.
On paper, it may seem like the Nova 7 will take better pictures than the iPhone X, particularly in poor lighting, because its 1.6µm pixels are larger than the iPhone’s 1.4µm pixels. But that’s not the case. As much as larger pixels play a part in picture quality, there’s more to it than just that.
Other things that affect picture quality are things such as the sensor, aperture, the quality of the optics, and so much more. Therefore, a smartphone that uses pixel binning will have to do more than just increase the size of its pixels to take better photos than one that doesn’t.
Advantages and disadvantages of pixel binning
|Creates larger pixels||Reduces image resolution|
|Improves picture overall quality||Does not support RAW|
|Reduces noise in low light|
Is pixel binning on smartphone cameras really necessary? Not really. A mobile camera with fewer megapixels and larger pixels does the job of mobile photography just fine. That’s why smartphones with many megapixels use pixel binning by default.
However, it is nice to have the option of shooting at high resolutions when the lighting is right if you wish to do so.
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