I've designed a catalog, using Illustrator CS4 and I have placed high resolution images into the document, which now has a file size of 1 GB. How can I reduce this file size to 20-30 MB? Thank you.
What you want to do, instead of dragging images into your .ai file, is to place (link) the images into the document.
FILE > PLACE
Make sure that "Link" is checked
Now your linked image is in your document
If you need to edit or update your links, go to WINDOW > LINKS
****IMPORTANT**** Using this method means that you must also send along any images that you have linked to the printer. What I recommend doing is having an "images" or "links" folder inside your main document folder (see below). I suggest that you place all of your images into your image folder BEFORE you link them. That way, your links will already be correct when you make them.
It's worth noting, however, that if you are sending a PDF to be printed, you don't need to worry about sending the images, as the PDF will have the images embedded within itself.