Have a look at some of the first software/hardware systems, which allowed to build detailed pixel art games.
Sega Digitizer System is a custom optical-pen based setup for in-house pixel artists, who worked at the Japanese company. There were 3 known version: Digitizer System I, II and III.
According to former Sega graphic designer AGE43, it was attached to a NEC PC-98 with an HDD. Since the Mega Drive was based on the System 16 arcade board, the Digitizer System could be used with both types of hardware. This particular software became an integral part of the production of some of the biggest games out there, including Fantasy Zone.
There’s not much known about the way they’ve used this system, but if you’re lucky you might find a documentary on NHK, where they discuss the game industry of that time. Anyway, modern tools are much more accessible and much more accessible to the general public, so you can now start building great games, without travelling hundreds of miles to another country.
Source: videogamesdensetsu.tumblr.com