Expert: Neal Ziring - 5/12/2006

Question
At what resolution should I start a picture if I want to expand it to "18 x 24"?  

Answer
Jim,

  Well, 18x24" is pretty big.  It will depend on the
resolution at which you hope to print your posters, but
at the least you'll want at least 1500x2000.  Many digital
cameras produce images of 1536x2048, which is 85dpi when
printed 18x24".  That is okay, but if the photo is highly
detailed you'll want more.

  In terms of resolution, a good size would be 2048x3072,
which is about 6 megapixels.  Really professional-looking
blow-ups will require even more; maybe 10 megapixels.  It
will depend on the kind of printer you plan to use.
For example, if you're going to use a 600dpi color printer,
then you'll want at least 100dpi on the image.

  Hope this helps...

...nz