Support KTX2 Texture Compression Format

[Lin Qin]

Hello,

Currently, most HTMLImageElement formats (e.g. JPEG / WebP / AVIF) focus on getting smaller size to download faster.

But video games (including WebGL) prefer texture compression formats which take much less memory (https://docs.unity3d.com/2020.3/Documentation/Manual/class-TextureImporterOverride.html).

Previously, the limitations of texture compression formats may:

    1. gpu raster is required;

    2. different platforms support different texture compression formats;

    3. some old formats (e.g. ETC2) are not smaller enough;

Now

    1. gpu raster is enabled by default;

    2. Basis Universal compression technology introduced in KTX2 can cross platform;

    3. ETC1S / ASTC can get smaller size.

         https://www.phoronix.com/scan.php?page=news_item&px=Khronox-KTX2-Format 

         https://github.com/ARM-software/astc-encoder/blob/main/Docs/FormatOverview.md#block-sizes

If HTMLImageElement supports texture compression formats, can reduce 75%~97% memory and some decoding time (or no decoding at all), then reduce power consumption.

The Khronos Group has published KTX-Software as open-source tools around dealing with KTX 2.0 compressed textures (https://github.com/KhronosGroup/KTX-Software).

I have tried integrated KTX-Software into chromium locally. It works well on Android.

So does it make sense to support KTX2 texture compression format?

[Ken Russell]

This is a great question. The main challenge in this area is reaching cross-browser agreement to support these "supercompressed" image formats in the <img> tag and elsewhere.

Does anyone else on this list have recent experience, or successes, adding new image or video formats to the web platform?

Alternatively - it looks like image/ktx2 is already registered as a MIME type - https://github.com/KhronosGroup/KTX-Specification/issues/18 . So perhaps Chromium can start accepting it, and web applications can target it via the picture element and:

   <source type="image/ktx2" ...>

as one option? And then other browsers can add support if they desire?

-Ken

[lexa.k...@gmail.com]

KTX2 is a generic container format that may contain almost any GPU texture payload; two supercompression schemes are just a part of that large set. On top of that, it supports 1D and 3D textures, cubemaps, arrays, simple animation sequences, channel swizzle and UV orientation metadata. KTX2 files also include a DFD block that provides EOTF and color primaries.

Should browser vendors add image/ktx2 as a supported picture source type, they would have to define a reasonable subset of KTX2 for web usage.

Keep in mind, that KTX2 supercompression codecs target VRAM usage; their network transmission size may be bigger than traditional formats like JPEG or PNG.

[Ken Russell]

Good points Alexey.

What would you think about supporting only the supercompressed subset of KTX2 payloads?

[Fredrik Hubinette]

Ohh, looks like it supports HDR! :)

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