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Re: [csswg-drafts] [css-color-hdr-1] Query 9: Black Level (#5322)

From: simontWork via GitHub <sysbot+gh@w3.org>
Date: Mon, 20 Jul 2020 11:39:50 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-660975668-1595245189-sysbot+gh@w3.org>
@svgeesus it's better in scene-referred video systems (e.g. BT.2100 HLG and  BT.709/BT.2020 SDR) to think of zero light rather than black.  In the broadcast signal, code value 64 represents zero light.

When setting up a professional video monitor, the brightness control is used to map code value 64 to the lowest perceptual level available given the light scattered from the screen. This takes in to account the ambient lighting level, display screen anti-reflectance technology etc.

To do this a signal called PLUGE is used (https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.814-4-201807-I!!PDF-E.pdf).  This has signals just above and just below code value 64, the brightness control is adjusted so that those above are just visible, whilst those below are not.

(In sRGB, the use of code value 0 is analogous to code value 64 in broadcast range BT.709/BT.2100)

Consumer displays have similar controls and some have a level of automation to try and achieve similar visual results. 

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Received on Monday, 20 July 2020 11:39:52 UTC

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