Reply To: Reducing/enlarging a placed image-how much is acceptable?

It all comes down to quality and your tolerance for seeing jaggies. For a pixel image that will be printed, you generally want to have 1.4 or 1.5 times your halftone frequency. In other words, if your printer says you'll be printing at 150 lpi, then you're going to want your images to have an “effective resolution” of about 225 ppi.

(Effective resolution means after scaling. The Links panel can show you your effective resolution.)

So if you import a 300 ppi image, you can scale it up to 125% and still get 225 ppi. (pixels per inch… some people call this dpi or dots per inch)

We wrote at great length about this in “Real World Scanning & Halftones” (you can probably still find the 3rd edition used somewhere!)