Re: Conversions for HDR Canvas Specification

Please, no long numbers!

And I’m not alone on this.




From: Chris Lilley <>
Date: Thursday, June 17, 2021 at 3:00 AM
To: "" <>
Subject: Re: Conversions for HDR Canvas Specification
Resent-From: <>
Resent-Date: Thursday, June 17, 2021 at 3:00 AM



On 2021-06-16 11:53, Simon Thompson - NM wrote:

Hi all,


I’ve added a list of suggested colour forward and reverse transforms between extended-sRGB, extended-linear-sRGB and bt2100-hlg and a suggested simple tone-mapping for displaying bt2100-hlg on an sRGB display to issue #50 -  I’ve tried to follow the style of the example in TTMLv2 provided by Pierre.


I can recalculate the matrices to a different number of significant figures if necessary – is there a consensus on accuracy levels for web operations? 

In general, since "space of the printed publication"is no longer a concern, I prefer to list to full precision.

I have seen several problems arising from round-off errors and round-tripping, so there is no good reason to round off.


Would Dolby colleagues be able to add the bt2100-pq versions to the list?  There is a PQ example in Pierre’s TTMLv2 link.


Best Regards






Simon Thompson 
Senior R&D Engineer

Chris Lilley
Technical Director @ W3C
W3C Strategy Team, Core Web Design
W3C Architecture & Technology Team, Core Web & Media

Received on Thursday, 17 June 2021 21:37:31 UTC