Band 0: what these captures record about light, and what they cannot

A 3D Gaussian splat scene stores, for every primitive, a position, a rotation, three scale terms, an opacity and a colour. The colour is normally spherical harmonics. Band 0 is the DC term, one RGB value that looks the same from every direction. The higher bands carry how the colour changes with viewing angle, and that is where specular on wet stone lives, and sheen on a leaf, and the way glass goes from near transparent to a hard white edge as you move past it.

I went and checked what the captures here actually ship rather than assuming. Every compressed PLY header lists packed_position, packed_rotation, packed_scale and packed_color and nothing else. There is no f_rest field. Every SOG meta.json carries means, scales, quats and sh0, and there is no shN key and no shN image anywhere on disk, at any level of detail, for any of the four publishers involved.

So four of these places are diffuse-only, and not because anything was dropped in transit. They are published that way.

That is worth saying plainly because it is a ceiling rather than a defect. No level-of-detail rung recovers it, no device-pixel-ratio cap recovers it, no post-process recovers it, because none of them can return information the source never contained. Recovering it means retraining from the original footage, which belongs to the photographers rather than to me. What is actually available on these four is resolution, splat count, and the sky and exposure the splats are lit against. Knowing which of those three levers exist has saved more renderer time than any of them have bought.

It also explains, more precisely than I had put it before, why captured motion is the direction. A splat carries radiance that was measured. A mesh dropped into the same street carries shading that was authored, out of a material I picked and a light I placed. Under one camera angle the two can be tuned until they agree. Move the camera and they stop agreeing, because one of them was measured and the other was guessed, and no amount of improving the mesh closes a gap of that kind. Band 0 or band 3, that argument holds.

The practical consequence is a change to how places get chosen. Whether a bundle ships shN is now something to check in the meta before committing to a capture, rather than something to find out afterwards.