Understanding Digital Camera Sensors (How Do They Work?)

Digital cameras revolutionized photography. Not only did they allowed more and more people to take up this hobby, but they also gave photographers much more control and creativity. But how many people actually understand how digital cameras work? At the heart of a digital camera is a sensor. This little piece is the reason we are able to capture photos in digital format rather than film. Don’t worry if you don’t know how they, here is a quick guide to understanding digital sensors.

What is a digital camera sensor?

A Digital Camera Sensor (DCS) is essential in a camera. Even if you don’t realize it, as it primarily regulates what your images end up looking like and how well they will scale up or print. There’s a long list of things that a DCS takes control of and helps when taking photographs, this list includes: image resolution, how the camera performs in low-light environments, dynamic range, and depth of field, and more.

How Do They Work?

There are two main ways that DCS’s work, the first way, creates a grayscale photograph, and the second way will produce a full-colour image.

A DCS creates a grayscale photo when you decide to take the picture and press the button. The DCS is exposed to light, which opens up the light cavities in a digital camera so they can collect photons which are stored as an electrical signal. After the exposure has been completed, the camera will shut the cavities down. Once these are closed, the camera will automatically total up how many photons entered each cavity – that is done by measuring how strong the electrical signal is. These signals are then assigned precise digital values and create a grayscale image because each cavity cannot distinguish how many of each colour they have. The way these values become so precise is because the camera uses ‘bit depth’ to determine them. When the file format has been recorded, the precision can be further reduced.

What is ‘bit depth?’

This aspect lets the camera know how many unique colours are available to it in its palette that is determined by the numbers of 0’s and 1’s used to identify each colour. In terms of grayscale images, the bit depth will identify the available unique shades, instead of colours.

If you’re taking a colour photograph, instead of all of the colours mixing in the cavity, a filter will cover each cavity, which will correspond to one colour and will block all other colours from entering. As a general rule with modern cameras, each cavity can only capture one out of three primary colours (red, blue, and green). The best arrangement is the ‘Bayer array,’ whereby rows of reds- greens and green-blues filters are arranged as shown in the image below. As you can see, this array has double the amount of green sensors than any other colour. Human eyes are less sensitive to blue and red light, so by using more green filters the image comes out looking sharper and with less noise (noise is more evident in reds and blues).

The next step in creating the image we see is by something called “demosaicing”. This is when the camera translated these primary colours into a full image that contains all of the colour information for each pixel.

Types of digital camera sensor

Much like how they work, there are also two critical types of sensors in modern digital cameras: CCD (charge-coupled device) and CMOS (complementary metal-oxide-semiconductor).

The CCD sensor, invented in 1969, was initially intended for storage but was never accepted for this purpose. The CCD sensor takes the charges off the chip and moves them to an amplifier found in the sensor. The signal is then changed from analogue to digital by an external circuit; the same circuit then stores the image on your memory card.

The CMOS sensor can change the data it receives for every individual pixel while the information is still in the sensor. This type of sensor can change in light conditions due to its ability to alter each pixel separately, which isn’t a quality held by CCD sensors.

These two sensor types are very similar, including the quality level and amount of sensitivity to light. The critical difference between how the sensor works is what happens once the light has been captured. Both kinds of sensors rely on the photoelectric effect, which will make an electric signal out of light.

The photoelectric effect is where particles have been electrically charged, which are then ejected from a material at the time it absorbs electromagnetic radiation.

Why have CCD sensors become more outdated compared to CMOS?

Since more and more newly released cameras now have CMOS sensors, they have much more range in lights and colours. CCD sensors are becoming less popular among manufacturers. This change began to show itself in 2015. One of the main reasons that CMOS overtook the CCD sensor is that it is much cheaper to manufacture, which will appeal to companies, especially those trying to save money on production. Additionally, it is said that Apple uses the CMOS sensor in its phones, and due to the rise in its popularity and evident appreciation from users for its camera quality, it is apparent that other companies would want to follow in their footsteps.

What are the best cameras?

As technology progresses, camera quality and ability have shown vast improvements. There are plenty of websites out there that list the best cameras that you can buy at the moment. But ultimately the best camera will differ one from one person to another and will be dependent on what it will be used for. For example, if you are a wildlife photographer, a camera with faster and more frames per second will be incredibly useful. Whereas, if you are only photographing for social media then you don’t need the pixel power of some of the latest DSLR cameras. The best camera is the one that you can afford and will be able to use regularly.

There you have it, a short guide to how digital sensors work. This of course just scratches the surface and if you would like to learn more about the science of digital sensors just search online. There are plenty of detailed articles that will go into more depth on this topic. But hopefully, you will now have a basic understanding of how digital sensors work.

Photo credits: Kav Dadfar – All rights reserved. No usage without permission. Dreamstime.