How do Smartphone cameras work?
Hey friends, Happy Wednesday!
I’m including an extended summary of how a gadget works in my newsletter, from which you can understand the essence in less than 3 minutes. But you can choose to read the blog posts for a more detailed version involving the nuances, from the links I attach.
Let’s look at how smartphone/digital cameras work this week. I aim to write my newsletter issues in a way one can follow them while traveling on a bus, having a coffee, waiting for your food, etc. Let's jump in!
Tweet of the week
I’m sharing a cool fact about gadgets every day on Twitter. And here is one of them for you.
How do Smartphone/Digital Cameras work?
There are several variations in the specifics of how a smartphone camera works. I’ve described the most common and basic variation here for you to get an idea. It consists of 5 steps. Let’s go!
Step 1: Light enters through the lens
1. The camera lens on the back of the phone captures the light from the scene you are trying to photograph. The lens is a piece of curved glass or plastic that sits in front of the camera's image sensor.
2. The lens serves to focus the incoming light onto the image sensor. This is done by bending the light as it passes through the lens. Different colors of light bend differently as they pass through a lens, as they are of varied wavelengths.
Step 2: Light is focused on the image sensor
Figure 1: Bayer Filter
When light enters the camera lens, it is focused onto the camera's image sensor. Its only job is to turn photons (light) into electrons (electrical signals). Most modern smartphones use CMOS (Complementary Metal-Oxide-Semiconductor) sensors, as they are cheaper, smaller, and consume less power.
The image sensor is a semiconductor device that is made up of millions of tiny light-sensitive pixels. Each pixel on the image sensor is made up of a photodiode and transistor. When light hits the photodiode, it generates an electrical charge proportional to the amount of light. The charge is then stored in the capacitor of the pixel, which is then read by the transistor (controlled by camera software) and converted into a digital signal.
This photovoltaic conversion happens at millions of photosites across the tiny surface of the sensor. If no photons reach the photosite, the sensor registers that pixel as black. If a lot of photons reach the photosite, that pixel is white.
But we need to record color photos and not black, white, or grey photos.
To capture color photos, smartphones use a color filter that sits on top of each photosite and only allows specific colors of light to pass through. The most commonly used color filter is the Bayer color filter array (Figure 1), which divides each 2×2 square of photosites into one red, one blue, and two green filters (RGGB). The Bayer array has alternating rows of red-green and green-blue filters, and twice as many green sensors as red or blue. This is because the human eye is more sensitive to green light than to red or blue, and thus green color receives a larger area compared to the other two primary colors.
Phones do not have a mechanical open/close shutter like traditional analog cameras. Instead, they use an electronic shutter that is integrated into the camera sensor.
When you press the button to take a photo on a smartphone camera, the camera's software activates the electronic shutter. The shutter works by instructing the camera sensor to turn on and off in a sequence of lines, starting from the top of the sensor and moving downwards at a rapid pace to capture the image. As each line is read, the camera sensor captures the light falling on it and converts it into an electrical signal. This process continues for each line of the sensor until the entire image has been captured. This method of capturing images is known as a "rolling shutter" because the camera sensor reads the image data line by line as it moves across the sensor.
Step 3: Electrical signals are converted into digital data
Once the image sensor captures the light and converts it into electrical signals, these signals are processed by a dedicated image signal processor (ISP) inside the phone. The ISP takes the raw image data and applies various image processing techniques, such as color correction, noise reduction, and sharpening to improve the quality of the image.
Step 4: Image Stabilization
Electronic image stabilization (EIS) is a digital technology used in smartphones using motion sensors to reduce the appearance of camera shakes and other types of motion blur in videos.
It detects the movement of the camera during video recording. The software then analyzes the motion data and applies corrective algorithms to the video frames to compensate for the camera movement and stabilize the image.
In order to compensate for the camera shake, the EIS system crops the video frame slightly and then shifts the frame in the opposite direction of the camera movement. The software then fills in the gaps created by the crop by using information from adjacent frames or by scaling up the remaining portion of the video.
Step 5: Displaying the Image
After the final image data has been recorded after the corrections, it is displayed on the smartphone's screen. The screen displays the image in real-time, allowing you to preview and adjust the picture before you decide to save it or discard it.
Gadget of the week
EV charging: The EVAR Parky Electric Vehicle recharging robot automatically finds and travels to your vehicle in a parking lot. Using image marker references, it finds your car and navigates to it using sensors. It then charges your vehicle.
Thank you for reading!
Have a nice rest of the week, and take care!
Until next Wednesday,
Chendur
