Would it be illegal to make a company that creates actual ink cartridges for various printers?

Everyone knows that nowadays, printers are pretty cheap but the ink costs so much more than it should. Ink cartridges don't even use all the space they have, so they appear much larger than they actually are. Let's say someone were to make a company that creates ink cartridges for various printers that actually use all the space they have for ink. Would this be illegal? It's probably a dumb idea but I'm just curious so please let me know. Thanks!