Poster image file size

[env]

Well, hallo to everybody.
I'm a newbie and I've a very simple question (not for me, tought):
I have to do an image that will be used for printing a color poster on paper in size 20" x 27"; the customer asked my to produce an image at 300 dpi, so I have to work with a very huge image from starting, and it's really difficult to add layers, apply filters and so on.
Does anybody know if this is the only or the correct way to make the job or if there is any good solution for work with a less big file? How have I to set the Gimp image size?
Thanks in advance

Env

 

[moldboy]

If your question involves changing the DPI I can't help you, but if you want to change the image size you can resize it to fit the poster size (don't make larger). The general rule. There are 100px to an inch. I would make the image a small as possable without going under to make the file easier to work with. Don't overwrite the origional!


Hope it helps