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What is Display Stream Compression (DSC)? VESA Display Compression Codecs

What is Display Stream Compression (DSC)

What is Display Stream Compression (DSC)? Display Stream Compression (DSC) is a configuration of visually lossless compression developed by the Video Electronics Standards Association (VESA).

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Also Read: List of the Best DisplayPort MST Hubs

This display standard is designed for use in ultra-high definition displays to decrease the bandwidth demand on the links between source material such as PCs, Blu-ray players, displays, and games consoles. From its launch in April 2014 to date, the DSC standard has attained broad acceptance in tablets and smartphones. Moreover, it will be used in future notebook PCs.

The technology makes 8K more practicable today and will explore even higher resolution displays and refresh rates in the future. Compression is the process of squeezing data to make sure it occupies less space.

Specifically, in the case of DSC, the compression is vital because the display standards like HDMI 2.1 and DisplayPort 1.4 are limited to 48 Gbps and 32.4 Gbps, respectively.

Related: How to Daisy Chain Multiple Monitors Using DisplayPort Multi-Stream Transport (MST)

Contrasting to lossy compression used in MP3 audio files or JPEG images, DSC is visually lossless. This implies that you will not perceive it while in use.

DSC enables you to reach faster refresh rates and higher resolutions on supported displays.

A few monitors need it to reach peak performance. Visually lossless implies no noticeable difference in the quality of the image or video when compression is executed.

Currently, DSC is integrated into standards used for embedded display interfaces in mobile systems. Such standards are the MIPI Display Serial Interface (DSI) specification v1.2 and later versions and VESA embedded DisplayPort (eDP™) Standard v1.4b.

The foremost DP standard which benefitted from the DSC 1.2b is the VESA DisplayPort™ (DP) 1.4a specification. It is backward compatible with DSC 1.1. DisplayPort 1.4 can unlock high refresh rates and higher resolutions on compatible devices.

VESA DSC facilitates visually lossless compression among the application processor and the display sub-system in UHD devices like tablets, mobiles, TVs, and AR/VR devices.

How did VESA DSC originate?

The need for compression on display links comes out due to the increased pixel counts of the higher resolution devices. So, it prominently increased the transport bandwidth required.

Though display resolutions in devices are raised every year, the PHY speed has not been increased as quickly. So, there exists a gap between the two. To handle additional bandwidth requirements on existing display links, VESA acknowledged the requirement for an industry-wide video compression specification which can work as a standard that bridged this gap.

The early application for DSC is battery-powered systems with an embedded display. This technology is used in the internal embedded display interface. In that case, it provides benefits like saving system power, an extension of battery life, reduction in the weight of the system form factor, and costs (by a reduction in the number of interconnected wires).

In the coming years, we will see DSC be used to enhance display resolution for external displays further.

To understand better, for example, DisplayPort 1.4a supports 8K video @ 60 Hz and 24-bit color via a low 2:1 compression ratio or 30-bit color via a low 2.5:1 compression ratio. Ultimately, it presents visually lossless image quality.

Feature Comparison – VESA DISPLAY COMPRESSION CODECS:

FeaturesDSC 1.1DSC 1.2aVDC-M 1.1VDC-M 1.2
Visually lossless compression performance verified by subjective testing
30 bit color, compression ratio (bits/pixel)3.75:1 (8 bpp)3.75:1 (8 bpp)5:1 (6 bpp)5:1 (6 bpp)
24 bit color, compression ratio (bits/pixel)3:1 (8 bpp)3:1 (8 bpp)4:1 (6 bpp)4:1 (6 bpp)
IC complexity1LowLowMediumMedium
Backward compatibilityDSC 1.xDSC 1.xVDC-M 1.xVDC-M 1.x
Both encoder and decoder are specified
Normative C language code
Frame-by-frame compression
8, 10, 12 bits per color support8/10/128/10/12/14/168/10/128/10/12
High Dynamic Range-ready
RGB and YCbCr 4:4:4 native encoding
YCbCr 4:2:0 or 4:2:2 native encodingNo
Image test database available from VESA
Compliance test guidelines and test scriptsIn Development
Publicly known adopting standardsMIPI DSI 1.2
DSI-2 1.0
VESA eDP 1.4b
HDMI 2.1
VESA DP 2.0
VESA eDP 1.4b
MIPI DSI-2 1.1MIPI (forthcoming)
= Available now
Information Source: https://vesa.org/vesa-display-compression-codecs/

What Does Display Stream Compression Do?

The reason why VESA DSC is the standard component of modern connectors is that it provides an approach to enhance the available bandwidth of HDMI and DisplayPort cables.

Essentially, it is a visually lossless compression algorithm with low latency based on the YCoCg color space. It implies that even though it reduces the bandwidth demands of higher refresh rate and higher resolution content, it is entirely untraceable by the viewer.

Practically, DisplayPort 1.4 with DSC is quite more competent than without it. The minimum bandwidth of DisplayPort 1.4 stays as it is at 32.4 Gbps. However, while the standard DisplayPort connection could support 4K @ 60Hz with HDR and 30 bits per pixel color depth, it can deal with either 4K @ 120Hz with HDR or 8K @ 60 Hz with DSC enabled.

DisplayPort hubs having DSC support can also benefit from DSC to simultaneously deal with multiple ultra-high-resolution displays. As a result, they streamline multiple display setups, chiefly those at higher resolutions.

You can buy DisplayPort Hubs from the below link:

The influence of DSC is more prominent with more competent, newer-generation standards. HDMI 2.1 can support 8K resolution at up to approx. 50 Hz as standard, along with 8 bits per pixel color depth. When Display Stream Compression 1.2 is used, it can handle 8K at 120 Hz or 10K at up to 100 Hz.

The new generation DisplayPort 2.0 standard will still show improvement. Independently it provides bandwidth more than what HDMI 2.1 can handle.

However, with support for the newer Display Stream Compression 1.2a, refresh rates and resolutions are far superior to anything else.

Moreover, it will enable 4K displays at up to 240 Hz. There is an option of two 8K displays operating at 120 Hz or a solo 16K display at 60 Hz.

Display manufacturers obtain extra benefits as well. Be the monitor or TV uses a DSC DisplayPort connector or DSC activated HDMI 2.1 connection, it can imply a reduced manufacturing expense, decreased demand on power consumption, and reduced requirement for interconnecting wires.

Thus, it increases the efficiency of stand-alone displays, extends battery life in mobile devices, and reduces electromagnetic interference.

Why is DSC used in DisplayPort?

  • The latest compression standard must be visually lossless because the content is frequently encoded with lossy compression like MPEG.
  • DisplayPort features need incredibly high bandwidth over the display link interface.
  • Very high resolutions ([email protected] 60/120 Hz and 8K @ 60 Hz) and equivalent data rates 8.1 Gb/s over a lane. DSC enables lower link rates to transmit a high video resolution.
  • Support for DisplayPort over USB-C interface
  • Multi-stream Transport (MST) needs more bandwidth.
  • USB-C DP Alt mode frequently uses only two DisplayPort lanes for transmission

DSC Over USB-C Could be the Future:

One of the key qualities of the DisplayPort standard, and through extension, DSC, is that other ports and cables could use it. Thunderbolt and USB-C technologies power DisplayPort for their audio and video transmission in DP Alt Mode. They can use VESA DSC for a higher refresh rate and higher resolution support.

By now, Thunderbolt cables, USB-C cables, and hubs efficiently power DisplayPort 1.4 with DSC. This makes it possible to connect a maximum of three 4K displays through a USB-C hub.

This is only the beginning because current-generation DSC DisplayPort 1.4 connections can allow data transmission at 8K resolution over Thunderbolt 3 and USB-C. Moreover, DisplayPort 2.0 will make Thunderbolt 4 and USB4 connections more competent.

Since the latest DSC generation will benefit, future USB-C monitors can execute at up to 16K resolution via Display Stream Compression 1.2a over USB-C connection.

Thunderbolt 4 and USB-C hubs can also power DSC for numerous super-high-resolution monitors. For example, they can power two 8K displays operating @ 120 Hz with HDR, or up to three 10K displays @ 60Hz with HDR enabled. This feature will be handy for those laptops that have next-generation integrated graphics.

Therefore, there will be a significant expansion of their available screen space, with no need for dedicated graphics or many onboard display outputs. Furthermore, it will increase the simplicity of daisy-chaining of super-high-resolution monitors.

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