Fwd: ISO 21496‐1:20XX Gain Maps

Forwarding, since Rich forwarded his original email to the list


-------- Forwarded Message --------
Subject:  Re: ISO 21496‐1:20XX Gain Maps
Date:  Wed, 15 Nov 2023 14:00:57 -0500
From:  Chris Lilley <chris@w3.org>
To:  Richard Geldreich <rich@binomial.info>



Hi Rich

On 2023-11-15 13:06, Richard Geldreich wrote:
> FWIW: From a glTF, real time rendering, video game, and browser 
> texturing perspective, unless Gain Maps /are 100% lossless/ with 
> respect to the interchange of IEEE 754-2008 half float pixels  (FP16), 
> this isn't a compelling solution for our use cases. We need no loss 
> whatsoever for denormals, all valid normals, signed values, all valid 
> 5-bit exponents, NaN's, and Inf's.
Absolutely. This gain map stuff isn't aimed at that use case *at all*; 
rather, at final content delivery to consumers. The ISO spec doesn't 
state that, but it is clearly the goal as I saw from the live demo I 
attended.
>
> PNG is a lossless format, and we need the ability to losslessly 
> interchange half float source textures and images while preserving 
> compatibility with existing 16-bit PNG software. We also need the 
> ability to store half float data in any colorspace, or even in no 
> colorspace: such as normal maps, which the use of SDR PNG's is 
> pervasive, or height maps, etc. (Both normal and height maps are 
> commonly viewable SDR PNG content right now.)
Yeah this wasn't trying to address what you have been discussing 
recently. They just happen to both use half floats (yours in the actual 
image, mine in a gain map).
>
> I searched this doc for "half" and found nothing.
The ISO spec is completely abstract and places no constraints on 
required precision, which I find surprising. That should be part of the 
feedback we send to them. It needs to be clear what the constraints are 
for lossless imaging (such as no down sampling, to take the most obvious 
one).

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