@Fizz similar but for games/engines that don't use uniform tile maps you basically just have a metadata set alongside the image that indexes where each sub-image is located in it.

It doesn't really change the end product, and as I said most engines already work like this for most 2d stuff, and many editors will pack for you if you tell them. You're just indexing portions of a texture, but it uses an order of magnitude less memory/storage and loads faster even off slow storage or web streaming.