Re: [EXTERNAL] Re: Proposal for HTMLCanvasElement HDR compositing modes

Hi All,

No, there's no OB truck in this scenario - for a live news event like that you would take the output of the camera direct to the broadcast hub via fibre network, 4G camera back or similar.  There would be no correction or shading other than the camera iris/white balance. Even in a larger event with an OB truck, for HDR live events I've yet to see an OB truck that has more than 1 HDR monitor.  The camera shaders normally control 4 or 5 cameras each by looking at either SDR outputs of the camera, a down-mapping of the HDR signal or the compatible image , so aren't monitoring the HDR signal at all.  The monitors are mainly used for focus checks, white balance etc.

I think this argument on terminology is better undertaken at the relevant ITU group.  Looking at Chris' proposal we have 3 systems:

  1.  A linear colour volume where 1,1,1 matches sRGB 1,1,1 - the meaning of which seems dependant on the operating system
  2.  A colour volume based on an EOTF with an absolute luminance range where we want to be able to insert signals at a fixed output luminance
  3.  A colour volume based on an OETF with a relative luminance range where the mapping to absolute luminance occurs in the display and we want to be able to insert signals at a fixed signal level.

I've been through Chris' document, it seems really good to me.  I have a couple of suggestions relating to narrow range to prevent artefacts in displays and asking clarifications.  I'm not an expert on Javascript, so have only undertaken a cursory look at the code examples.

Looking forwards to chatting in person.

Best Regards

Simon

--
Simon Thompson MEng CEng MIET
Senior R&D Engineer
BBC Research and Development South Laboratory


________________________________
From: Pierre-Anthony Lemieux <pal@sandflow.com>
Sent: Tuesday, March 16, 2021 18:14
To: Simon Thompson-NM <Simon.Thompson2@bbc.co.uk>
Cc: Kevin Wheatley <kevin.wheatley@framestore.com>; Todd, Craig <CT@dolby.com>; Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com>; Jim Helman <jhelman@movielabs.com>; Lars Borg <borg@a1830.dscd.akamai.net>; Christopher Cameron <ccameron@google.com>; public-colorweb@w3.org <public-colorweb@w3.org>
Subject: Re: [EXTERNAL] Re: Proposal for HTMLCanvasElement HDR compositing modes

> This camera signal will be transmitted to a broadcast centre and then directly on to a distribution network without any form of colour correction, shading or grading.

.... so the camera is set up to generate images that look right on the
broadcast reference monitor in the truck, right?

On Tue, Mar 16, 2021 at 11:07 AM Simon Thompson-NM
<Simon.Thompson2@bbc.co.uk> wrote:
>
> Hi,
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> Neither ITU-R BT.709 nor ITU-R BT.2100 are defined by how an image looks on a reference monitor, as there are many occasions where the video is not checked on a reference monitor.
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> As an example, covering a live event in ITU-R BT.709, say a demonstration or interview at an event, the viewfinder would have Zebras set to a known level, say 75% for Caucasian skin tone or 45% for grass.  The cameraman would then adjust the Iris so that the relevant area of the image had Zebras illuminated.  The camera would have been set up previously – the only reference is the signal level that the Zebras are set to.  Quite often cameramen still use B&W viewfinders so there is no reference colour.
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> This camera signal will be transmitted to a broadcast centre and then directly on to a distribution network without any form of colour correction, shading or grading.
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> Best Regards
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> Simon
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> Simon Thompson
> Senior R&D Engineer
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> BBC Research & Development
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> From: Kevin Wheatley <kevin.wheatley@framestore.com>
> Sent: 16 March 2021 17:45
> To: Todd, Craig <CT@dolby.com>
> Cc: Simon Thompson-NM <Simon.Thompson2@bbc.co.uk>; Seeger, Chris (NBCUniversal) <Chris.Seeger@nbcuni.com>; Jim Helman <jhelman@movielabs.com>; Lars Borg <borg@a1830.dscd.akamai.net>; Christopher Cameron <ccameron@google.com>; public-colorweb@w3.org; Pierre-Anthony Lemieux <pal@sandflow.com>
> Subject: Re: [EXTERNAL] Re: Proposal for HTMLCanvasElement HDR compositing modes
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> On Tue, 16 Mar 2021 at 15:44, Todd, Craig <CT@dolby.com> wrote:
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> BT.2100 is a more complete specificaton as it includes specs on the reference display and reference environment.
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> BT.709 display was de-facto CRT. When new display technologies became available it was necessary to explicitly define the HDTV display. This was done in two separate Recs, BT.1886 spec'd gamma=2.4 and BT.2035 specs white at 100 nits and a viewing environment with a 10-nit background. I consider HDTV a display referred system, i.e. you create a pixel to produce known color/luminance on the reference display in the reference environment.
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> yes, I'd actually consider 709/1886 display referenced too because  the effective rendering transform from scene to display is defined in terms of the viewing conditions, most edits made to the signal are made on a monitor without transforming back to scene linear, and most outputs from cameras today do not encode using the Rec 709 OETF in the first place, at least not for any of the content we see.
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> Certainly when it comes to mapping content mastered in one set of reference condition to the specific use cases we always map to reference display colourimetry and then back through the new display/conditions on the assumption that the mastering environment needs to be preserved and is often unknown what the actual scene colorimetry might have been and what transformations have been applied as a rendering.
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> I'd do pretty much the same approach for HLG, even though it is possible to obtain HLG unedited from a camera and thus get some focal plane referred relative scene linear, people want images to "look the same" as they saw on some monitor, rather than some vague recollection of the scene. This basically makes images practically display referenced the moment you edit them whilst viewing on a monitor.
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> Kevin
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> --
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