RE: Sanity check, ITU and IEC definitions of sRG are identical, right?

Note that the ITU document is a Report (informative) and not a Recommendation (which would  be a normative specification).

Craig Todd
Dolby Fellow
Dolby Laboratories
1275 Market St.
San Francisco, CA  94103
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From: Chris Lilley <>
Sent: Wednesday, May 1, 2019 8:18 AM
Subject: Sanity check, ITU and IEC definitions of sRG are identical, right?

Learned people,

Currently, all W3C specifications (bar one, which is being fixed [1]) refer to the IEC definition of sRGB as authoritative. [2]

Multimedia systems and equipment - Colour measurement and management - Part 2-1: Colour management - Default RGB colour space - sRGB<>.

However, the link goes to the IEC web store[3], where one can pay real money for a copy. In consequence, many people don't have a copy (including myself, hence this mail).

I recently learned [4] (and sorry, I didn't know this before) that sRGB is also defined by the ITU, on p.14 of:

Television colorimetry elements. Report  ITU-R  BT.2380-2 (10/2018)<>

and this specification has the merit of being freely available to download.

I see that the ITU report does reference IEC 61966-2-1 so I presume that the chromaticity coordinates, EOTF and OETF are copied correctly from there.

I notice that the EOTF breakpoint is specified to more significant figures, 0.40449936 rather than 0.04045 which I have seen elsewhere.

I would have greater peace of mind, before submitting a pull request on the spec database to point to the freely available specification, if someone who has read both specifications could confirm for me that the definitions are identical?

[1] Web Content Accessibility Guidelines refers to an obsolete 4th working draft of the IEC specification, which still has the erroneous rounded-off coefficient that led to a discontinuity in the transfer function.
Although the impact on 8bit per component systems is invisible, I now have agreement to fix that<> and following


Chris Lilley


Technical Director @ W3C

W3C Strategy Team, Core Web Design

W3C Architecture & Technology Team, Core Web & Media

Received on Wednesday, 1 May 2019 15:50:08 UTC