Embedded vision is quickly gaining more prominence in Artificial Intelligence (AI), the Internet of Things (IoT), and other emerging technology based applications. Hence, more companies are looking to cost-efficiently integrate imaging capabilities into their products. For many such products and applications, Mobile Industry Processor Interface (MIPI) is one of the most popular and convenient ways of interfacing cameras with the host processor.
In this blog, we attempt to learn more about the MIPI interface and how MIPI cameras work.
Before we even get into the advantages of the MIPI interface and how MIPI cameras work, let us talk a bit of history on how the interface evolved over time.
Evolution of the MIPI interface
CSI-1
CSI-1 was the original standard MIPI interface architecture that defined the interface between a camera and a host processor.
CSI-2
Released in 2005, the first version of MIPI CSI-2 came with a protocol divided into layers, such as:
- Physical Layer
- Lane Merger Layer
- Low-Level Protocol Layer
- Pixel to Byte Conversion Layer
- Application Layer
Later in 2017, the second version of MIPI CSI-2 was released along with support for RAW-16 and RAW-20 color depths. In addition, it could increase virtual channels from 4 to 32, and reduce Latency Reduction and Transport Efficiency (LRTE).
The third version of MIPI CSI-2 was released in 2019 and came with support for RAW-24 color depth.
CSI-3
MIPI CSI-3 was first released in 2012 followed by the next version in 2014. It provided a high-speed and bidirectional protocol for image and video transmission between cameras and hosts.
Among the three types, MIPI CSI-2 is the most commonly used interface in mobile and remote applications like autonomous driving, drones, smart city, medical imaging, computer vision, etc.
More about MIPI CSI-2
In the previous section, we looked at how the MIPI interface evolved through the years. Now, let us try to understand the MIPI CSI-2 interface a bit more in detail.
Commonly used in embedded vision systems, MIPI CSI-2 is a camera interface that connects an image sensor with an embedded board to control and process the image data. This helps the sensor and embedded board to act together as a camera system to capture images. The below image represents an embedded camera board connected to an image sensor using a MIPI CSI-2 interface.
MIPI cameras provide higher performance by ensuring better resolution and frame rate than the older parallel interface camera module a.k.a. the Digital Video Port (DVP) interface.
Today, many engineers prefer MIPI CSI-2 cameras over USB cameras. While both cameras come with their own pros and cons, let us look at some of the key advantages of MIPI cameras over USB.
Why MIPI CSI-2 over USB?
In theory, the maximum bandwidth of the USB interface is 5 gigabits per second. Practically, you could attain a bandwidth of about 3.6 gigabits per second.
This limits the ability of vision systems used in many applications to transfer image data fast for various processing and analysis purposes. That is where CSI-2 can be more helpful. It offers a maximum bandwidth of 6 gigabits per second, with an attainable bandwidth of roughly 5 gigabits per second). CSI-2 also makes the process more efficient and faster when compared to the general-purpose interface in USB.
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Prabu is the Chief Technology Officer and Head of Camera Products at e-con Systems, and comes with a rich experience of more than 15 years in the embedded vision space. He brings to the table a deep knowledge in USB cameras, embedded vision cameras, vision algorithms and FPGAs. He has built 50+ camera solutions spanning various domains such as medical, industrial, agriculture, retail, biometrics, and more. He also comes with expertise in device driver development and BSP development. Currently, Prabu’s focus is to build smart camera solutions that power new age AI based applications.