Dark Souls Remastered | Entering the Painted World of Ariamis then to first bonfire, full cutscene

This is an entirely optional area.

To access this place, you must return to the Undead Asylum via the Giant Crow, then acquire the Peculiar Doll, now waiting in the cell where every player starts the game, then interact with the painting at the bottom floor of the chapel in Anor Londo.

That's the room that you have to go through by walking on the rafters while Painting Guardians throw knives at you. It isn't necessary to go to the bottom floor of this area and neither is entering the painted world (these areas are optional).

A return trip to the Undead Asylum is also optional. To do so:
https://youtu.be/hApINlpUALQ