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The revolution of digital cameras began with the introduction of digital image sensors. In the early 1980s and late 1970s, cameras began taking digital images thanks to the adoption of CCD (Charge-Coupled Device) sensors. These sensors, which were initially developed for use in scientific applications, worked by converting light into an electrical signal that could be processed by a computer. Initially, CCD sensors were quite expensive and could take pictures at a very limited resolution. This made them unsuitable for consumer-level cameras, which were dominated by film cameras at the time. However, advancements in semiconductor technology soon made it possible to produce smaller and more affordable CCD sensors, paving the way for the development of the first consumer-level digital cameras.
Then, in the mid-2000s, CMOS (Complementary Metal Oxide Semiconductor) sensors began to gain popularity in digital cameras because of their capability of allowing each pixel to process its own data instead of transferring image data from one pixel to the next like in CCD sensors. This made using CMOS sensors more cost-effective and efficient as they required less power to operate. As a result, this technology was then later adopted into smartphone camera modules.
And thus, in this article, we are going to be looking at the different variants of camera sensors and how the technology has evolved. We are mainly going to be looking at four types of sensors:
Это первая в мире CMOS-матрица с разрешением более 1 мегапикселя с такими характеристиками.
Sony анонсировала новую революционную разработку: компания создала 1,46-мегапиксельную CMOS-матрицу с обратной засветкой (BSI) и центральным затвором. Это первая в мире CMOS-матрица с разрешением свыше 1 мегапикселя с такими характеристиками.
BSI — технология, при которой засветка матрицы происходит с обратной стороны, что позволяет увеличить количество полученного света. Это, в свою очередь, позволяет улучшить качество работы в условиях слабого освещения. Раньше подобные матрицы использовались главным образом в астрофотографии или в камерах наблюдения, но сейчас эта технология все больше применяется и в потребительских фотокамерах.
В 2015 году Sony a7R II стала первой полнокадровой камерой с BSI-матрицей; в 2017-м Nikon D850 — первой камерой с BSI-матрицей разрешением более 45 мегапикселей.
Но все эти BSI-матрицы — с построчным считыванием, то есть пиксели кадра считываются не одновременно, а ряд за рядом, пусть даже и очень быстро. В большинстве случаев разницы между двумя вариантами считывания нет, однако если камера или объекты в кадре движутся во время съемки, при построчном считывании возникают искажения.
Искажения, возникающие при построчном считывании, на примере быстро движущихся лопастей пропеллера
https://youtube.com/watch?v=dNVtMmLlnoE%3Ffeature%3Doembed
Новая разработка Sony представляет собой матрицу с обратной засветкой (BSI) и с функцией центрального затвора, что позволяет считывать все пиксели кадра одновременно. Это — выдержка из технического описания матрицы на сайте Sony:
“Новый датчик Sony получил новейшие компактные слаботочные конвертеры, расположенные под каждым пикселем. Они мгновенно конвертируют аналоговый сигнал со всех пикселей в цифровой, чтобы временно сохранить его в цифровой памяти. Такая архитектура позволяет избежать искажения, вызванного задержкой считывания, что позволяет реализовать функцию центрального затвора.
Чтобы добиться параллельной конвертации всех пикселей, Sony разработала технологию, благодаря которой стало возможно использовать примерно 3 миллиона соединений Cu-Cu (“медь-медь”) в одной матрице. Такое соединение обеспечивает электрическую непрерывность между пикселем и слоем управляющей логики, одновременно обеспечивая пространство для 1,46 миллиона конвертеров (по количеству эффективных пикселей)”.
Это — пример фото, снятого с помощью новой матрицы (обратите внимание на отсутствие искажений у вращающихся лопастей вентилятора):
Пока нет никакой информации, когда эта революционная разработка появится в потребительских камерах, но уже очевидно, что Sony намерена удержать свое господство в области производства датчиков изображений и обеспечить своим цифровым камерам первенство в плане качества матриц.
What is a Stacked Sensor?
Stacked Sensors are the next evolution of imaging sensors that are slowly being adopted to be included in high-end photography equipment. The key differentiating factor of these sensors is that they combine multiple layers of imaging components into a single, compact unit. In a traditional image sensor, the photodiodes, amplifiers, and output circuits are typically positioned on a single layer. This can lead to limitations in performance and complexity in design.
In this section, we are going to be primarily talking about all the types of imaging sensors and how they differ from one another. However, we are not going to be covering CCD sensors extensively in this section as these sensors have gone somewhat extinct after the introduction of CMOS and more advanced sensors like BSI and Stacked.
CCD Sensors
Despite their age, CCD sensors still have a certain appeal to them for being the first digital camera sensor. But is nostalgia the only factor at play or can these sensors actually hold up in today’s time? Well, here are the noteworthy pros of CCD sensors.
Of course, there are several notable cons of using CCD sensors as well.
CMOS Sensors
What’s interesting about CMOS sensors is that most of the sensors that we use today are a rendition of CMOS. In other words, it means that CMOS sensors are used as the base for most camera technology that we are familiar with. Some of the pros of using cameras with CMOS sensors are:
As widely accepted CMOS sensors are, they also have certain drawbacks to them:
BSI CMOS Sensors
BSI CMOS sensors are some of the most widely used camera sensors out right now. As a matter of fact, Apple has been using this sensor for their phones since the iPhone 4. And it is still being used in the latest iPhone 14 series of smartphones. Here are some of the pros that make the BSI sensors stand out:
BSI sensors do suffer from a couple of drawbacks too.
Stacked Sensors
Although Stacked Sensors are still relatively new, this technology has huge potential to revolutionize the camera market. To note a few of its primary advantages:
Similar to BSI sensors, Stacked sensors also suffer from similar issues, such as:
CCD vs. CMOS vs. BSI CMOS vs. Stacked Sensor
Till now, we have seen how all of these different sensors work, what makes them different, and the pros & cons of using them. Unfortunately, there isn’t exactly a clear winner here.
“CCD sensors are great for those who love the style of classic digital images, CMOS is for those who are looking for a camera sensor at an affordable range, BSI sensors will appeal to people who enjoy taking stunning night-time photographs, and Stacked Sensors are a combination of all of the aforementioned sensors but comes at a premium cost.”
Regardless of which one you go for, you are bound to get value out of all of these sensors.
What is a CCD Sensor?
As we have briefly touched upon, a Charge-Coupled Device, or a CCD sensor, is a circuit system that is used to capture pictures by converting the photons from light into an electronic signal. This signal is then processed by a computer to transform it into a digital image. CCDs were the first commercially used sensors in a wide variety of digital photography equipment. They operate by using a grid of light-sensitive pixels to capture the incoming light. When light strikes a pixel, it creates an electrical charge, which is then transferred from one pixel to the next until it reaches a charge-to-voltage converter. The converter then converts the accumulated charge into a voltage signal, which is processed by the camera’s processing chip to produce a digital image.
What is a BSI CMOS Sensor?
What is a CMOS Sensor?
CMOS, or Complementary Metal Oxide Semiconductor sensors, were introduced as a natural evolution to CCD sensors. Although both of these image sensors do the exact same thing, their mechanism of processing images is quite different. Each pixel in a CMOS sensor is equipped with its own photodiode, amplifier, and output circuit. When the photodiode comes into contact with light, it creates an electrical charge, which is then amplified and processed by the output circuit. This output circuit transforms the electrical signal into a digital signal, which is then handed over to the camera’s computing chip for processing. These digital signals are then turned into digital images (JPEGS, RAW, etc.) after being formatted from raw data.
