How do search engines treat redirects for a site change?

I have a website that is a PR3 with a majority of traffic through Google Images. I am looking at rebranding it with a different name and URL. My question is, if I automatically redirect users to the new domain does that mean the site loses its PR and have to start over again? Or does that somehow transfer over to the new site. Also, how many problems will this create with Google. Will Google begin indexing new pages at the new location and automatically flushing out the old domain ones or do they have to be manually removed?

Thank you for your help!

 

If you 301 redirect it will be fine.

 

i've read that every single page should do a 301 to the new corresponding page.

 

When 301 redirecting don't just redirect the whole site, redirect pages to new pages of the same theme.