Why is the image sensor more important than the number of megapixels?

Camera quality is one of the most important factors in every smartphone, which is why it becomes a race for phone manufacturers. Behind each beautiful photo is a small image sensor in the camera (or as we now call it, the camera cluster). Nowadays, the larger the number of megapixels, the more people expect, but the size of the image sensor is the most important. So why is this tiny image sensor so important in helping the camera work so well?

To understand this, we need to return to the most basic principle in photography, which is capturing light. A larger image sensor can capture more light, and more light results in better images. At least in theory that's the case.

Catch as much light as possible

At a basic level, the size of the sensor determines how much light the camera will capture to create an image. While resolution plays a role in determining detail, the amount of light captured determines exposure balance, dynamic range, and even sharpness. That's why a DSLR camera with 16MP resolution still delivers better photos than a 108MP smartphone camera.

Most image sensors on smartphones are only about 1/2.55 inch or 1cm long, sometimes there are phone models equipped with large image sensors that are only 1/1.7 inch or a little larger. For comparison, DSLR camera sensors are typically about 4 to 5 times larger than phone sensors. Currently, Huawei P40 is a smartphone equipped with the largest image sensor on the market (1/1.28 inch).

The larger the image sensor, the easier it is to adjust shutter speed, ISO, and aperture. Although you can use exposure skills to compensate for the disadvantages of the small image sensor, your photos will be extremely blurry due to the unstable grip and movements of the object. No matter how high the resolution is, it cannot overcome this problem. And you probably guessed it, a large sensor takes better low-light photos than a small sensor.

The camera's photosites, the tiny parts responsible for converting images from light to electronic signals, require light. They can be arranged in different ways depending on the sensor, but usually on phones it will be a pixel/photosite. The more light a photosite receives, the more dynamic range (the exchange between light and shadow) will be produced. We can see this clearly when we receive a bright image with little noise.

Photosites come in many different sizes, depending on the resolution of the camera and the size of the sensor. A constant image sensor means photosites can shrink as resolution increases. Instead, with the resolution maintained, the larger the photosite, the larger the image sensor.

 Why is the image sensor important?

As phone camera resolutions become increasingly larger (now over 100MP), image sensors play an even more important role. Keeping pixel sizes reasonable is essential to maximize the potential of 48, 64 and 108MP camera resolutions. However, phone cameras cannot fully exploit this resolution. The image sensor has to work hard to capture as much detail as possible in good lighting conditions.

Another recent trend in phones is pixel binning technology, which allows high-resolution sensors to combine pixels to create well-lit photos. The large sensor, now with expanded pixels, has quickly improved the quality of photos taken in low light conditions. The result of this technology is better colors, less noise, even in low light environments.

Large image sensors also affect image quality in addition to resolution. As mentioned above, a fast shutter speed and low ISO range will make your photos more detailed and sharp.

Compare sensors on phone cameras

Currently on the smartphone market there are countless different photo sensors, here we will talk about some high-end models.

It won't be until 2020 that some smartphones can surpass the 1/1.5 inch sensor on the 2013 Nokia Lumia 1020, a monument of phone cameras. Large sensors are certainly not a new idea, but few companies follow this formula.

 Google Pixel 4 and iPhone 11 rank last in the top flagship image sensors, but they are the devices with the best camera quality. Obviously, the image sensor is not all that is needed to create a beautiful photo.

A missing piece of the puzzle

Large image sensors play an important role in phone cameras, but they are not the only ones. A good quality camera needs to have a standard lens, a powerful image processing chain and optimized software.

David Pac

Update 13 October 2023