The update enables advanced machine vision applications in various application areas such as mobile, augmented and virtual reality, drones, Internet of Things (IoT), medical devices, industrial systems, vehicles and end devices (tablets, notebooks and all-in-one systems).

Building on the machine awareness capabilities introduced in MIPI CSI-2 v3.0, version 4.0 offers an always-on imaging solution that operates over just two cables. This reduces cost and complexity for ultra-low power machine vision applications. CSI-2 v4.0 also adds multi-pixel compression for the latest generation of image sensors and RAW28 color depth to optimize image quality and signal-to-noise ratio (SNR).

MIPI CSI-2 was originally introduced in 2005 and has become the world's most widely used interface for embedded cameras and imaging systems, according to the MIPI Alliance. As a high-speed protocol for the transmission of still and video images from image sensors to application processors, it supports a wide range of use cases that require high performance, low power consumption and low electromagnetic interference (EMI). Typically implemented for shorter range applications on a MIPI C-PHY or MIPI D-PHY physical layer interface, version 4.0 supports for the first time the transmission of CSI-2 image frames over the low cost, low pin count MIPI I3C/I3C Basic two-wire interface. CSI-2 can also be implemented via the MIPI A-PHY SerDes long-range interface (up to 15 m), which is suitable for applications such as advanced driver assistance systems (ADAS), vehicle infotainment and the industrial IoT.
New features of the specification include:

• Always-On Sentinel Conduit (AOSC): enables always-on machine vision systems whose combinations of ultra-low power image sensors and video signal processors (VSP) continuously monitor their environment and wake up their more powerful host CPUs only when important events occur. (Typically, the VSP is either a separate device or integrated with the host CPU in a larger SoC). Application examples include laptop/tablet-based facial surveillance, video surveillance and optical driver assistance and safety systems. With AOSC, image data can be streamed cost-effectively from an image sensor to a VSP via a low-power MIPI I3C bus. Scaling options are available to add additional I3C lanes and bandwidth according to the I3C specification.
• Multi-Pixel Compression (MPC): Provides optimized pixel compression for the latest generation of Tetra and Nonacell image sensors with multi-pixel color filter arrays (CFAs). The MPC feature helps reduce the high bandwidth requirements of these sensors by compressing both multi-pixel and normal Bayer CFA images more efficiently and with potentially higher quality than current methods. Reference code has also been provided to assist integrators in evaluating the algorithm and verifying their implementations.
• RAW28 pixel encoding: Supports the next generation of high dynamic range automotive image sensors for applications such as those required for ADAS and other safety-critical applications.

CSI-2 v4.0 is backwards compatible with all previous versions of the MIPI specification, is available to MIPI Alliance members and can be downloaded via the member portal on the MIPI Alliance website.

The MIPI Alliance (MIPI) develops interface specifications for the mobile industry and industries influenced by mobile applications. Every smartphone manufactured today contains at least one MIPI specification. Founded in 2003, the organization has over 325 member companies worldwide and 14 active working groups that develop and deliver specifications for the mobile ecosystem.