With everyone demanding the best camera phone, image quality has become the latest smartphone arms race. And the camera sensor is where manufacturers highlight it. While high megapixel count is an increasingly popular trend as we’ve seen on phones like the Galaxy S24 Ultra, the size of the camera’s image sensor is actually much more important. HUAWEI, Samsung and others are also making a bigger deal with the bigger image sensors packed into their latest generation smartphones. But why is camera sensor size seemingly so crucial to capturing the best photos?

To understand why, we need to go back to the fundamental principle of photography — capturing light. A larger sensor captures more light than a small one, and more light produces better images. But there’s more to it than that, especially in the age of computer photography.

Editor’s note: This article was originally published in March 2020 and has been updated to reflect the latest developments in large camera sensors.

Why does camera sensor size matter?

At a basic level, sensor size determines how much light the camera has available to create an image. While resolution plays an important role in detail, the amount of light captured determines exposure balance, dynamic range, and even camera sharpness. This is why 16MP and 20MP DSLRs still look better than today’s 200MP smartphones.

Most smartphone sensors are typically only 1/2.55 inch or about 1 cm in diameter, although higher-end smartphones increasingly have sensors 1/1.31 inch and larger. By comparison, DSLR camera sensors run over an inch, easily making them 4 or 5 times larger. Smartphone sensors are simply tiny in comparison, although a few brands are narrowing the traditional point-and-shoot sensor size gap. Sony Xperia Pro-I, Xiaomi 14 Ultra and others are some of the largest in the mobile industry with a diagonal of 1 inch.

The larger the sensor, the more light it captures for the set shutter speed, ISO (exposure sensitivity) and aperture. Although you can compensate for the sensor’s slight shortcomings with a longer exposure for more light, this makes images more susceptible to blurring due to handling and scene movement. blur reduces image sharpness regardless of sensor resolution. Similarly, lenses with wider apertures are more difficult to make without introducing lens distortion artifacts, not to mention changing the field of view. As you’ve probably guessed, more light makes larger sensors much better at low-light photography than smaller ones.

The photographic sides of the camera, the bits responsible for converting the scene into electrical signals, love light. They can be arranged in different ways depending on the sensor. Newer smartphones used traditional Bayer sensors that are equivalent to one pixel per photo spot. Although modern high-definition phone cameras have turned to Quad Bayer sensors that have more than four or even nine pixels per photo spot. In other words, four pixels share a single color filter, which, through a technique called pixel binning, mimics the attributes of larger photo pages. More on that later.

In any case, the more light the photosites receive, the better the dynamic range (visible steps between light and dark) they can produce. Think of it as “assurance” that any pixel is lighter or darker than its neighbors. It’s much easier to estimate this with lots of light hitting the sensor and minimal noise.

Photo pages vary in size depending on camera resolution and sensor size. Keeping the sensor size constant means that the photosite size decreases as the resolution increases. Alternatively, for a set resolution, the larger the photosites, the larger the sensor becomes.

This is important to keep in mind because photo pages are crammed together in small sensors. Their close proximity means that occasionally light from one pixel leaks into the neighboring pixel. This is sensor noise and can often be seen very clearly in low-light images and in solid colors such as blue skies. Smaller sensors and small photo slots increase noise and reduce dynamic range. Samsung is trying to solve this problem with its ISOCELL camera sensor technology.

With the move to higher and higher resolutions (now above 100 MP), larger camera sensors have never been more important. Keeping pixel sizes reasonable is key to maximizing the resolution potential of 48, 64 and 108 MP cameras. Although we have yet to see a smartphone camera that pulls out the full level of detail you’d expect from these figures. Despite this, these sensors capture more detail than ever in good lighting.

A recent trend in the mobile space is pixel binning technology, which allows these high-resolution sensors to combine pixels to better capture light. These larger sensors, and thus larger pixels, significantly improve the quality of low-light photos. This results in less noise and much better colors, even in dimly lit environments. Quad Bayer pixel-binning cameras can also produce impressive HDR images.

Larger sensors, in addition to resolution, affect the appearance and quality of your shots. As we mentioned earlier, faster shutter speeds and lower ISO ensure that your images look clear and sharp. You also don’t need as wide an aperture to capture a lot of light, reducing the chances of lens distortion, such as purple halos due to chromatic aberration.

Larger sensors also affect the focal length of the image which in part produces that fancy bokeh blur effect we associate with DSLRs, where the subject looks isolated and the rest of the image is blurred. For a fixed aperture, the depth of field narrows as the sensor size increases, creating more noticeable foreground and background blur. While small mobile sensors can’t match the performance available with a DSLR, larger sensors help close the gap.

Smartphone Sensor Comparison

To showcase the wide range of image sensors currently available in the smartphone space, we’ve tracked the main sensor sizes in a range of high-end phones over the past few years.

It was necessary until 2020/2021. that a good number of smartphone cameras surpass the 1/1.5-inch sensor size offered by the 2013 Nokia Lumia 1020, the historic titan of mobile photography. Larger sensors are certainly not a new idea, but companies are now willing to accept the aesthetic compromises that go hand in hand with larger sensors.

It’s also worth mentioning that older flagships like the Google Pixel 5 and iPhone 11 ranked at the bottom of modern flagship sensor sizes, but were still considered some of the best camera phones of their generation. It’s clear that sensor size isn’t everything when it comes to taking a great photo. Computational photography and intelligent software can also help improve image quality.

Larger image sensors are an important piece of the mobile photography puzzle, but they’re not the only one. A great quality camera also requires a brilliant lens, a powerful image processing chain and software that allows you to get the most out of the hardware as easily as possible. It’s important to look at the whole package, not just one part or the big numbers on the spec sheet.

Smartphone camera quality is also increasingly driven by advances in computational photography and machine learning. Check out the affordable Google Pixel 7a, which continues to punch above its weight despite its old and small sensor. Smart software can beat raw megapixels for image quality. Even so, great software can only do so much with bad hardware. Intelligent cameras need a solid base to build on, and image sensor size is a key ingredient in the race for better smartphone cameras.