Scan resolution requirements for postcards

[zxiong@xxxxxxxxxxxxxxxxxxxxxx]

Hi everybody,

I'm seeking advice from the forum regarding scan resolution requirements for
postcards printing via full color presses.  Any help would be greatly
appreciated.

I have a variety of photos taken with Noblex 135U, Fuji 690s, and 35mm Nikon.
The originals are all in Velvia.  I can also print them on Ilfochrome paper.
In fact I prefer Ilfochrome prints to originals for many of them either 
because the colors on the Ilfochrome prints look nicer or because some of the
originals are imperfect in exposure or need slight color manipulations.  

Now the question is what the requirement for scan resolution for the highest
quality 4 color press is?  I know drum scan is perhaps the best solution but
I wonder if such high resolutions offered by a drum scanner may actually
overkill the resolutions achievable on best printers (for postcard sized
photos of course).  People told me that the best print resolution was 150 to 
200 lpi and the relation of dpi to lpi was about 2 dpi = 1 lpi,  which means
that a resoltion of 400 dpi should be adequate.  This can readily be done on a
flatbed scanner working on the real size photo and the digital file would be
about 20 MB in size.  

I would appreciate it very much if anyone with experience could answer my
question, or simply tell me if a 20 MB digital file in TIF format would render
the highest achievable print quality for postcard-sized photos.  I'm asking 
this question because if the answer is yes I can do the scanning myself.  My
flatbed scanner can do 1200 dpi but that would produce a 100MB digital file
for a postcard-sized photo which my computer cannot handle.  

Regards,

Zonghou Xiong