In article ,
Eric Greenwell wrote:

Fortunately, Tom was able to persuade them to use his 2 megapixel
picture, which is about 160 dpi. It takes about 7 megapixels for 300
dpi, and it's simply not neccessary if it's a high quality picture that
uses the full frame.

As someone who designs and implements halftoning screening systems
professionally (see http://www.megadot.co.nz/) I agree that using images
with a dpi exceeding the lpi (lines per inch) of the halftoning
screening is not necessary or useful on most natural images (people,
scenery). This is typically something like 175 lpi in glossy magazines.

It is pretty important though to not have the photo dpi be only slightly
different to the halftoning lpi for aliasing reasons -- either make it
*exactly* the same, or else make it different (higher) by a factor of
1.5 or more.

Hard diagonal edges between contrasting colours do benefit from higher
dpi, right up to the basic resolution of the imagesetter used (typically
either 2400 or 3386 dpi). 1200 dpi is about the lower limit for really
crisp looking text. Nothing looks worse than hard-edged jaggies. If in
doubt use PhotoShop to resample your image to 300 dpi or 2x the printing
lpi (if you know it) using bicubic interpolation. That will create
enough anti-aliasing to avoid jaggies on the printed page. And the
magazine editor will never know :-)

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------