CamCyclopedia
Contents
- Working of an Image Sensor
2. Resolution and Size of Image Sensor
3. Colour Filter of Image Sensor
4. Image Sensor of Galaxy Camera
5. Notes
Working of an Image Sensor
The structure of the Galaxy Camera is very similar to the structure of the human eye. The image sensor described here resembles the retina of the human eye and it acts as the film of a regular film camera.
In human eyes, the image of the subject that we look at is formed in the retina through the lens, and this image is delivered to the brain through the optic nerve. Likewise, in Galaxy Camera, the final image that we see is completed only when the image sensor converts the optical signal of the image delivered through the lens into an electrical signal and sends it for Image Signal Processing (ISP) in the Application Processor (AP).
Then, shall we find out more about this image sensor?
Like in the picture below, the optical signal on the image sensor is concentrated through the Micro lens and the colour information that passes through the Colour Filter reaches Photodiode or the light detector [4] as an optical signal (Photon). The photodiode produces electrons, which are electrical signals, depending on the size of the incoming optical signal. This is converted to a digital signal using an image sensor internal circuit (ADC: Analog Digital Converter and Logic circuit) and then sent to the ISP of AP.
Pixels can distinguish 3 kinds of colours- Red (R), Green (G), and Blue (B) through the colour filter on the photodiode. Brightness information can also be obtained through this since more electrons are generated if the incoming light is brighter.
Generally, larger the size of the pixel, the more light enters the photodiode in proportion to the pixel size, helping produce a brighter image in low light. However, if you use good pixel technology such as Samsung’s ISOCELL [5], it will provide a better image signal in low light, even at the same pixel size.
Resolution and Size of the Image Sensor
If you look at the rear camera specifications of S22 Ultra [6] on the Galaxy homepage, it will appear as follows.
There are a total of four cameras at the back. The first one is an Ultra Wide Camera with a 12MP resolution having a 120-degree field of view, and the second one is a wide-angle camera with a 108MP resolution image sensor. If the camera resolution is high, you can take a picture or a video with better detail. This is why you can take a picture or a video with the highest resolution when you shoot using a wide-angle camera.
The 3rd and 4th cameras, which are telephoto cameras with 3x and 10x optics respectively, are both equipped with image sensors of 10MP.
Apart from this, pixel size and sensor size information are also indicated in the specifications. You can find out more about F.No. [7] and Auto Focus (post expected) from another Camcyclopedia article.
As shown in the table below, a resolution of at least 2MP is required to provide FHD (1080p) video, and a resolution of at least 8.3MP is required for a 4K video.
Therefore, a sensor with high resolution provides better details, and this is evident from the difference that we see when we compare FHD and 4K video on a TV or a monitor. Hence, an image sensor with a resolution of at least 33MP and above is required for an ultra-high resolution 8K Video.
With this in view, the wide-angle camera is mounted with an ultra-high resolution sensor of 108MP in models starting from Galaxy S20 Ultra to deliver an image with intricate details like the picture that you see below. Moreover, in the S22 Ultra, this was upgraded to the next level through a Deep Learning algorithm known as Detail Enhancer.
Does this imply that high-resolution sensors are always good? The optical format below shows the size of an image sensor. The diagonal length of the image sensor is typically displayed as 1/1.8", in inch format. Usually, the size of the image sensor determines the size of the lens required. So, when the size of the resolution of the image sensor is increased, the size of the sensor increases which means that it requires a larger lens, thus consequently increasing the height of the camera module. This is what leads to the commonly talked about ‘Camera bump’.
Therefore, we need a technology that can provide high resolution without increasing the size of the image sensor, to avoid an unsightly camera bump. Hence, we applied a small pixel of 0.8um in the wide-angle camera of Galaxy S22/S21/S20 Ultra. However, it was mentioned above that improved sensitivity and good images in low light can only be provided when the size of the pixel is large.
Then, how does the Galaxy S22 Ultra camera manage to deliver good pictures with small pixels?
This is what we call Adaptive pixel technology. This feature uses two cameras- a 108MP sensor and a 12MP sensor to take a picture and merges it as one through software processing, rendering a final image that is smaller in size while at the same time retaining the details captured.
The following picture illustrates how the 108 MP sensor works in low light. The picture shows that the 108 MP sensor is a collection of nine pixels, where nine 0.8um pixels combine to form 2.4um and act as a single pixel in low light. However, in a situation where a 108MP image is required, the 9 pixels operate separately and provide a picture with good details.
Colour Filters of Image Sensor
As shown in the picture below, pixels are arranged with three colour filters, consisting of Red, Green, and Blue, which is called the Bayer colour filter pattern [8] after Bryce Bayer, the person who invented this filter.
A sensor with a resolution of 12MP means that it comprises 6M Green pixels and 3M Red and Blue pixels each. This image sensor follows the method of placing two Green filter elements, which are the most sensitive to brightness, and one each of Red and Blue alternately in the intersecting area, as seen in the arrangement below.
However, the structure of Bayer Pattern makes it difficult to enable the operation of multiple pixels as one. Hence, it is hard to apply the Adaptive pixel technology mentioned above.
Fortunately, other solutions are available to resolve this. The illustration below shows that structures such as the Tetra pattern or Nona pattern can make multiple small pixels operate as one large pixel in low light.
Thus, the S22/S22+ wide-angle camera that has an image sensor of 50MP uses the Tetra pattern. In low light, it delivers a 12.5MP image by turning 4 pixels of each colour into one 1.6um pixel and if high resolution is required, each of them operates separately to provide a 50MP image.
Starting with the S20 Ultra wide-angle camera, the 108MP image sensor has a Nona pattern, which in low light can deliver 12MP images with nine pixels of each colour operating as one pixel, and even provide ultra-high resolution images of 108MP.
Image Sensor in Galaxy Camera
The below picture shows the image sensors used in the Galaxy camera of Galaxy S20~S22.
The 108MP wide-angle camera sensor, which delivers good images in both low light and ultra-high resolution, was added to the Ultra models starting from S20. While for S21 models and above, one more sensor was added, bringing the total count of sensors at the back to four. Additionally, for S22/S22+ models, a 50MP wide-angle camera sensor was applied to non-Ultra models also, to provide greater detail.
The strength of Galaxy camera image sensor technology lies in the details it provides, hence, we are relentlessly preparing to get closer to ultra-fine video expression by taking advantage of this technology.
So, stay tuned for the next Galaxy Camera!
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