(wrong string) ‐1:20XX Gain Maps

Gain maps, in their current proposed form, are a secondary image that is applied to the primary image (via standardized algorithms) to enable going between HDR and SDR renderings.  At this time, all examples have been on integer pixel formats – not on half (or full) floats – but there is nothing in the design that would prevent that.  Someone (you?) should review the algorithms to make sure that they will work on floating point data – but IIRC it shouldn’t matter the encoding of the values.

As to some of your other PNG requirements – those are happening in other threads and not relevant here.

Leonard

From: Chris Lilley <chris@w3.org>
Date: Wednesday, November 15, 2023 at 2:05 PM
To: public-png@w3.org <public-png@w3.org>
Subject: Re: ISO 21496‐1:20XX Gain Maps

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Thanks for putting that discussion on the public record, Rich.
On 2023-11-15 13:24, Richard Geldreich wrote:
(I sent this earlier to Chris, without CC'ing the PNG Working Group.)

>Gain Maps are an (allegedly) efficient way to provide an SDR baseline
image plus an HDR alternate image. The claim of storage efficiency has
not been backed up by any measurements that I have seen.

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.

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.)

I searched this doc for "half" and found nothing. The only mention of quality was with respect to the SDR image. Gain Maps also look more complex vs. just storing remapped half values in the PNG file, involving a resample stage for example. The source data for this approach (the "Image File" in this diagram from the doc below) would be an HDR image, even a "haLf" float PNG image.
[cid:part1.t3wqZ4cS.yVBBu1o0@w3.org]

--

Chris Lilley

@svgeesus

Technical Director @ W3C

W3C Strategy Team, Core Web Design

W3C Architecture & Technology Team, Core Web & Media