USING PHOTOSHO AND INDESIGN LARGE SCALE DESIGN

It works for all occasions Bob as long as you enter the minimum intended viewing distance. If that will be less than 2 feet then by all means go for 300ppi.

The maths is based on this  :

A good human eye can resolve 60 line pairs per degree i.e. pairs of black and white lines.  So in half a degree we would have 60 single lines.

Simple trigonometry means that the width containing those 60 lines can be calculated by:
               Width of 60 lines = Viewing distance x tan(0.5°)

Once we know the width for 60 lines (or pixels) we can calculate how many lines per inch can be seen by using 60/Width of 60 lines.

So putting those together gives us
60/(Viewing distance x tan(0.5°)) = 60/(Viewing distance x 0.0087269)  = 6878/Viewing distance

Dave

How close will the images be viewed? 300 ppi is for images seen at close distance e.g holding a book. As we step away our eyes can make out less and less detail.

A simple formula for ppi is :
ppi required  = 6878/Viewing distance in inches

Anything above that is wasted as our eyes just can't resolve it.

Dave

Also, some stock agencies have interpolation capability that allows them to blow up an image with no pixel damage, more than we can do on our own. Did you download the largest available size from Getty?

Check with your printer, sometimes designs can be scaled to 1/2 size and the printer can blow it up.  If not you can try resizing in Photoshop using Preserve Details 2.0 enlargement and see if the results are acceptable.  Otherwise, you may need larger original images.