Based on materials from GSMArena
In December, the first smartphones with 48 MP cameras appeared, and now we are seeing their unexpected dominance. Interestingly, a significant part of them belongs to the middle segment, while many flagship devices are equipped with a 12 MP sensor. What's the matter?
And the fact is that a quadruple Bayer filter has appeared. And since marketing departments in companies are often unable to clearly explain what kind of sensor it is, you will have to do this work for them.
What is a Bayer filter?
Let's start with the basics. The Bayer filter is a color mosaic of red, green and blue filters that allow the digital sensor to capture color images. Semiconductor pixels do not 'see' colors, they only collect the amount of light that hits them, so without a filter, you just get a black and white frame. The Bayer filter ensures that the light hitting each pixel has one of three primary colors.
As a result, in a 12 MP sensor, 6 million pixels 'see' green and 3 million pixels each – red and blue. An algorithm called demosaicing is used to interpolate a full 12MP image.
The name 'quadruple Bayer filter' is somewhat misleading in and of itself, because it is actually no different from a conventional Bayer filter. And not the filter itself has changed, but the sensor – in the new sensor, each color square corresponds to four pixels, not one.
So, in reality, these 48MP quad sensors do not provide more detail than 12MP sensors. Sensor manufacturers will tell you that smarter demosaicing algorithms will allow you to convey more detail, but from experience, the gain here is small, if any.
Where can you find quad Bayer filters?
Recently, 48 MP sensors are the most popular – dozens of smartphones are equipped with them. It all started with Huawei and its 40MP sensors in the P20 Pro, Mate 20 Pro and Mate 20 X. The Chinese company even installed a second version of the sensor in Huawei P30 and P30 Pro, where the sequence the colors were red – yellow – yellow – blue instead of red – green – green – blue, but the principle remained the same.
There are also several smartphone models with 32MP selfie cameras with quad Bayer filters, such as the Vivo V15 Pro and Samsung Galaxy A70. They have the same pixel size (0.8µm), but they are physically smaller, so they have a lower resolution.
Samsung recently announced a 64MP quad Bayer filter, and again has the same pixel size, but the size of the sensor itself changes – it is 33% larger than the current 48MP sensor.
What is a Quad Bayer filter sensor capable of?
As already stated, the true power of the quadruple filter is not at all where it is sought. Thanks to it, the group of four pixels that make up the color square of the filter can act as one or as separate sensors.
Since its inception, these are some of the largest sensors ever installed in a smartphone. For example, the Sony IMX586 – the first 48MP sensor and one of the most popular – has a diagonal size of 8mm. The IMX363, which is used in the Pixel 3, and the Samsung S5K2L4, which is in the S10, measure 7.06mm diagonally. This is about a 30% increase in area.
However, the pixel size is very different, 0.8µm for 48MP sensors and 1.4µm for traditional sensors. All marketing materials about 48MP sensors emphasize that they can use pixel binning and can act as if the pixel size was 1.6µm.
This creates a 12 MP image. The 1.6µm size is something that is often talked about, but it is not something that can completely solve the problem of sensor performance in low light conditions. The appearance of noise is a random process, and if a large pixel of a traditional sensor perceives noise instead of a signal, there is little that can be done about it (except that it can be compensated by interpolating data from neighboring pixels).
However, if one of the four pixels of a quad-filter sensor catches noise, only 25% of the information is lost – and this reduces the noise by four times without reducing the sharpness of the image.
Alternatively, the sensor can be split into two logical sensors, one for short exposures and the other for long exposures. This option is used in daylight for real-time HDR shooting.
You can reduce noise and shoot in HDR with a conventional sensor rather than a quad sensor, taking two (or more) frames one after the other, and then combining them. This is what Pixel smartphones do, and they do the job quite well.
However, there is a problem: moving objects change position when shooting with sequential exposures. And a Quad Bayer filter takes two shots at the same time, so no artificial intelligence is required to correct artifacts caused by subject movement. This is what a failed correction looks like.
Sequential exposure HDR shot
HDR Snapshot with Quad Bayer
Here's the simplest way to explain how a Bayer Quadruple Filter works: It allows the camera software to take two shots at once. This makes it possible to apply image processing in HDR and night mode, which is why modern smartphones take high quality photos – the hardware part does not differ significantly.
What are the capabilities of the technology?
Unlike LCD, where each pixel has a red, green and blue subpixel, in a conventional sensor there is only one subpixel per pixel. But at the same time, it would be impossible to talk about such a high resolution, since these pixels are located close to each other and the restoration of the original image occurs due to demosaicing (although people who are able to distinguish pixels everywhere will always say that it is not perfect).
Samsung Galaxy A80: 12MP
Samsung Galaxy A80: 48 MP
In a quadruple Bayer filter, pixels of different colors are farther apart, and demosaicing is less effective (whatever the manufacturers say). So in the case of 48 MP, you don't get 4x better detail than 12 MP. In fact, when HDR and other 48MP processing modes are turned off, 12MP photos sometimes come out with even better detail (and weigh less, which is a double benefit!).
When the demosaicing algorithm is applied to the original data at 48 MP, a sharper image can be obtained, but in the case of different devices and different scenes, the result will be different. And if detail is critical for a particular shot, it's best to photograph in both modes and then choose the best shot. And most of the time, you should stick to the 12 MP mode.
Oppo Reno 10x zoom: 12 MP
Oppo Reno 10x zoom: 48 MP
Not to mention that reading a full 48MP image was beyond the capabilities of some early sensors and chipsets, so they just took a 12MP image and zoomed it in – which was a waste of free space.
One of the most frequently cited benefits of Quad Bayer sensors is better zoom. While the Nokia 808 PureView had an impressive zoom, its huge 41 MP sensors had a conventional Bayer filter. As already discussed, a quad Bayer filter can give only a small gain in sharpness (or maybe not), so in reality there is no difference with a digital zoom on 12 MP sensors.
Asus Zenfone 6: 12 MP
Asus Zenfone 6:48 MP
Marketing departments are working hard to make you believe that your smartphone has a Hasselblad-like sensor, and in fact a Quad Bayer filter is just a smart (and effective) way to improve the quality of 12MP images.
Huawei 20 Pro: 12 MP
Huawei 20 Pro: 48 MP
And also optics matters. Without going into details, these high-resolution cameras often have diffraction limitations, which means that the smallest point of light cannot be focused on an area smaller than a pixel. Read about Airy's disk. In general, there is a physical limitation on the maximum resolution that compact optics and sensors can have.