What is a GLB and GLTF file?
GLB is a 3D file format that is most commonly used in web-based applications. It comes with its set of textures and animations. The reason this format is used for web-based applications is because its small in size.
Well, what is a GLTF then? Well to simply it GLB is a version of GLTF which is GL Transmission Format. In GLTF some data is stored in external files like images etc.
Using a GLB file
If you are working with a GLB file, and you want to reduce its texture size, then the best approach would be to import that file into a 3d creation application and then export it as a GLTF file, thus splitting the content that is inside the GLB file and then you can access the textures that way.
For that I would recommend using Blender, as it is free and open source. Once blender is downloaded simply import the GLB model into the application, and without changing anything simply export the file back, but this time export it in GLTF format.
Once that is done, you will see that you now have access to the different image textures. Now you can open them up in photoshop or any photo editor of your chose and optimize its texture size and resolution.
Now if you need to use the GLB extension at the end, simply import the GLTF file back in blender and export as GLB, and that’s it. Your texture size issue is resolved.