OpenEXR. Though it probably could use a spec upgrade, in particular add JPEG-XL to the list of compression algorithms. It’s not like OpenEXR’s choices are bad, the lossy ones are just more geared towards fidelity than space savings.

Bonus: Supports multi-channel, so not just RGBA. Not terribly useful for your run off the mill camera, very useful in production where you might want to attach the depth buffer, cryptomatte etc and I guess you could also use it for the output of light field cameras. Oh there’s also multi-view so you can store not just stereo images but also whole all-around captures and stuff. There’s practically nothing pixel-related you can’t do with it though it might require custom tooling.