Display Stream Compression: Difference between revisions

Revision as of 17:42, 15 October 2020

Revision as of 13:42, 8 January 2023

Line 1:

{{Short description|Video compression method for HDMI and DisplayPort links}}

#REDIRECT [[DisplayPort#Display Stream Compression]]

{{Infobox technology standard

#REDIRECT| title = [[DisplayPort#Display Stream Compression]]

{{Redirect category shell|

| ___domain = [[Video compression]]

{{R to section}}

| status = In force

| logo =

| image =

| caption =

| organization = [[VESA]]

| related_standards = [[HDMI]], [[Display Port]]

| year_started = 2013

| website = {{URL|https://vesa.org/vesa-display-compression-codecs/dsc/}}

}}

''Display Stream Compression'' (DSC) is a [[Video Electronics Standards Association|VESA]]-developed video compression algorithm designed to enable increased display resolutions and frame rates over existing physical interfaces, and make devices smaller and lighter, with longer battery life.<ref name=DSC>{{cite press release |url=https://www.vesa.org/news/vesa-finalizes-requirements-for-display-stream-compression-standard/ |title=VESA Finalizes Requirements for Display Stream Compression Standard |publisher=VESA |date=24 January 2013 |access-date=20 March 2018 |archive-url=https://web.archive.org/web/20180321130439/https://www.vesa.org/news/vesa-finalizes-requirements-for-display-stream-compression-standard/ |archive-date=21 March 2018 |url-status=dead }}</ref> It is a low-latency algorithm based on [[delta modulation|delta PCM]] coding and [[YCoCg|YC{{sub|G}}C{{sub|O}}-R]] color space.<ref name=DSC /><ref name=vesa-etp200>{{cite web |url=http://www.vesa.org/wp-content/uploads/2014/04/VESA_DSC-ETP200.pdf |title=VESA Display Stream Compression |last1=Walls |first1=Frederick |last2=MacInni |first2=Sandy|date=3 March 2014 |publisher=VESA}}</ref> Although DSC is mathematically [[Lossy compression|lossy]], it meets the ISO/IEC 29170 standard for "visually lossless" compression, a form of compression in which "the user cannot tell the difference between a compressed and uncompressed image".<ref>{{cite journal |last1=Walls |first1=Frederick |last2=MacInnis |first2=Alexander Sandy |title=27.4L: Late-News Paper : VESA Display Stream Compression: An Overview |journal=SID Symposium Digest of Technical Papers |date=June 2014 |volume=45 |issue=1 |pages=360–363 |doi=10.1002/j.2168-0159.2014.tb00097.x}}</ref> ISO 29170 more specifically defines an algorithm as visually lossless "when all the observers fail to correctly identify the reference image more than 75% of the trials".<ref name=ISO29170>{{cite web |title=ISO/IEC 29170-2:2015 — Information technology — Advanced image coding and evaluation — Part 2: Evaluation procedure for nearly lossless coding |url=https://www.iso.org/standard/66094.html |website=iso.org |publisher=[[ISO|International Organization for Standardization (ISO)]] |ref=ISO29170 |___location=Geneva, Switzerland |format=PDF |date=August 2015}}</ref>{{rp|18}} However, the standard allows for images that "exhibit particularly strong artefacts" to be disregarded or excluded from testing, such as engineered test images.<ref name=ISO29170 />{{rp|13,18}} Research of DSC using the ISO/IEC 29170 interleaved protocol, in which an uncompressed reference image is presented side by side with a rapidly alternating sequence of the compressed test image and uncompressed reference image,<ref name=ISO29170 />{{rp|10}} and performed with various types of images (such as people, natural and man-made scenery, text, and known challenging imagery) shows that in most images DSC satisfies the standard's criterion for visually lossless performance, although in some trials participants were able to detect the presence of compression on certain images.<ref name="Sudhama">{{cite journal |last1=Sudhama |first1=Aishwarya |last2=Cutone |first2=Matthew |last3=Hou |first3=Yuqian |last4=Goel |first4=James |last5=Dale |first5=Stolitzka |last6=Jacobson |first6=Natan |last7=Allison |first7=Robert |last8=Wilcox |first8=Laurie |title=Visually Lossless Compression of High Dynamic Range Images: A Large-Scale Evaluation |journal=SID Symposium Digest of Technical Papers |date=May 2018 |volume=49 |issue=1 |pages=1151–1154 |doi=10.1002/sdtp.12106 |url=https://static1.squarespace.com/static/565e05cee4b01c87068e7984/t/6000baf6782fa205430dc4b6/1610660599845/Sudhama_Allison_Wilcox_2018SID.pdf |access-date=4 March 2021}}</ref><ref name="Mohona">{{cite journal |last1=Mohona |first1=Sanjida |last2=Au |first2=Domenic |last3=Kio |first3=Onoise |last4=Robinson |first4=Richard |last5=Hou |first5=Yuqian |last6=Wilcox |first6=Laurie |last7=Allison |first7=Robert |title=Subjective Assessment of Stereoscopic Image Quality: The Impact of Visually Lossless Compression |journal=2020 Twelfth International Conference on Quality of Multimedia Experience (QoMEX) |date=May 2020 |pages=1–6 |doi=10.1109/QoMEX48832.2020.9123129 |url=https://ieeexplore.ieee.org/document/9123129 |access-date=4 March 2021 |___location=Athlone, Ireland|isbn=978-1-7281-5965-2 |s2cid=220073001 }}</ref>

DSC compression works on a horizontal line of pixels encoded using groups of three consecutive pixels for native 4:4:4 and simple 4:2:2 formats, or six pixels (three compressed containers) for native 4:2:2 and 4:2:0 formats. If RGB encoding is used, it is first converted to reversible YC{{sub|G}}C{{sub|O}}. Simple conversion from 4:2:2 to 4:4:4 can add missing chroma samples by interpolating neighboring pixels. Each luma component is coded separately using three independent substreams (four substreams in native 4:2:2 mode). Prediction step is performed using one of the three modes: modified median adaptive coding (MMAP) algorithm similar to the one used by [[JPEG-LS]], block prediction (optional for decoders due to high computational complexity, negotiated at DSC handshake), and midpoint prediction. Bit rate control algorithm tracks color flatness and buffer fullness to adjust the quantization bit depth for a pixel group in a way that minimizes compression artifacts while staying within the bitrate limits. Repeating recent pixels can be stored in 32-entry Indexed Color History (ICH) buffer, which can be referenced directly by each group in a slice; this improves compression quality of computer-generated images. Alternatively, prediction residuals are computed and encoded with [[entropy coding]] algorithm based on delta size unit-variable length coding (DSU-VLC). Encoded pixel groups are then combined into slices of various height and width; common combinations include 100% or 25% picture width, and 8-, 32-, or 108-line height.

A modified version of DSC, ''VDC-M'', is used in [[Display Serial Interface|DSI-2]]. It allows for more compression at 6&nbsp;bit/px at the cost of higher algorithmic complexity.<ref name="VESA Codecs">{{cite web |title=VESA Display Compression Codecs |url=https://vesa.org/vesa-display-compression-codecs/ |website=VESA - Interface Standards for The Display Industry}}</ref>

DSC version 1.0 was released on 10 March 2014, but was soon deprecated by DSC version 1.1 released on 1 August 2014. The DSC standard supports up to a {{ratio|3:1}} compression ratio (reducing the data stream to 8 bits per pixel) with constant or variable bit rate, RGB or [[YCbCr|{{YCbCr}}]] [[chroma subsampling|4:4:4]], 4:2:2, or 4:2:0 color format, and color depth of 6, 8, 10, or 12 bits per color component.

DSC version 1.2 was released on 27 January 2016 and is included in version 1.4 of the DisplayPort standard; DSC '''version 1.2a''' was released on 18 January 2017. The update includes native encoding of 4:2:2 and 4:2:0 formats in pixel containers, 14/16 bits per color, and minor modifications to the encoding algorithm.

On 4 January 2017, [[HDMI 2.1]] was announced which supports up to [[10K resolution]] and uses DSC 1.2 for video that is higher than 8K resolution with 4:2:0 [[chroma subsampling]].<ref name=HDMI21PressRelease>{{cite news |url=http://www.hdmi.org/press/press_release.aspx?prid=145 |title=HDMI Forum announces version 2.1 of the HDMI specification |publisher=HDMI.org |date=2017-01-04 |access-date=2017-01-10}}</ref><ref name=HDMI21Introduction>{{cite news |url=http://www.hdmi.org/manufacturer/hdmi_2_1/index.aspx |title=Introducing HDMI 2.1 |publisher=HDMI.org |access-date=2017-01-10 |archive-date=6 January 2017 |archive-url=https://web.archive.org/web/20170106195344/http://www.hdmi.org/manufacturer/hdmi_2_1/index.aspx |url-status=dead }}</ref><ref name=HDMI21January2017Anandtech>{{cite news |url=http://www.anandtech.com/show/11003/hdmi-21-announced-8kp60-48gbps-cable |title=HDMI 2.1 Announced|author=Anton Shilov |publisher=Anandtech |date=2017-01-05 |access-date=2017-01-10}}</ref>

[[Category:VESA]]

[[Category:Video compression]]