I'm not sure about "passthrough". If I was a user and I saw this parameter, I would assume "passthrough" means "pass through IR but literally do nothing", meaning I would assume it would also not change the format (to WEBP for example). "Passthrough" to me doesn't imply widths will be passed through.

Some alternatives: "passthroughWidth", or `"width": null`. I think I would prefer the latter