Allow Base Color and Alpha Map textures to NOT be combined on export

[wiledal]

Funnily enough, this has been requested in reverse previously: #343

Problem
Since glTF-files are often used in web applications, it is crucial to keep the filesizes low.
Having JPEG-compressed diffuse+alpha material combos is often 500%+ more size efficient than transparent pngs.

My example scene is 600kb as FBX, with separate JPEG diffuse and alpha textures.
Same scene is 4.3 MB when exported to .glb from Blender, due to the creation of transparent PNGs.

While the combined texture can be useful, it would be great to have the option to keep the alpha channel separate from the diffuse texture in the export settings.

[scurest]

Separate base color/alpha textures are not possible in glTF.

[wiledal]

I just realized this ☝️ after looking at the glTF spec. For a format that is built to be portable and web-friendly, this is an obvious disadvantage in regards to file sizes. But I don't know enough about the underlying ideas to justify my criticism.

Maybe we can use avif textures in the future, with considerably better image compression. Except, that is also not part of the spec.

[donmccurdy]

There are texture formats available or upcoming in glTF that include alpha at better file sizes than PNG:

• webp (via EXT_texture_webp)
• KTX / Basis Universal (via KHR_texture_basisu)

But Blender does not support these formats (yet?) so the image compression would need to be added after export.

You may also be able to improve the default compression of PNG images with something like https://squoosh.app/.

[wiledal]

I considered using other image formats externally, but keeping the files self-contained is part of what makes it great.

Closing this since the topic is related to the glTF spec rather than the Blender exporter.

[metamultiverse]

Hi, is there any update on this issue since last comment?

[julienduroure]

Do you refer to webp & KTX / Basis? Because the first request of this ticket is not something the glTF specification allows.

About webp : Still in the TODO list, not planned for now. News will probably goes in this ticket : #1308

About KTX: Much more complicated, KTX must probably be added in Blender core first, before we can managed it in I/O. No visibility on this for now

[metamultiverse]

Hello Team, Thank you for reply. This issue was regarding Alpha map support for Gltf. We wanted to know if it got solved after gltf 2.0 update. Currently alpha maps are not working with glb directly. Thanks Siddhesh

…

-- *Siddhesh Narvekar* * CEO & Founder E-mail: ***@***.*** www.tapmyads.com On 29 November 2022 at 2:05:57 PM, Julien Duroure ***@***.***) wrote: Do you refer to webp & KTX / Basis? Because the first request of this ticket is not something the glTF specification allows. About webp : Still in the TODO list, not planned for now. News will probably goes in this ticket : #1308 <#1308> About KTX: Much more complicated, KTX must probably be added in Blender core first, before we can managed it in I/O. No visibility on this for now — Reply to this email directly, view it on GitHub <#1230 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMU6XWVKG4AGJO5P6Y5A7RDWKW563ANCNFSM4SAIVG7Q> . You are receiving this because you commented.Message ID: ***@***.***>

[donmccurdy]

@metamultiverse No, glTF requires alpha to be in the alpha channel of the base color texture. You're welcome to file an issue on the glTF repository (https://github.com/KhronosGroup/glTF/issues), I don't know of any open requests for the feature (or plans to add it) at the moment.

[ArturBalthazar]

The problem is when we want to use a different UV channel for the alpha texture. Bc if it's combined with base color, they are forced to use the same uv channel, which is sad and limiting... :(