PNG stacks are problematic

[martinweismann]

File sizes can be very high:

• narrowband storage of sdf
• delta compression
• group 4 compression on 1 bit channel
• openexr / openvdb

Speed:

• writing and decompressing can be slow

[martinweismann]

PNG should be good enough for now, especially with https://github.com/3MFConsortium/spec_volumetric/issues/12 .

Conclusion: We do a first version with PNG only, but might open that up for other formats/representations later.