Slide scanning - scan to print size or best resolution ava..

This may be perceived as a stupid question but I use an on-line photo
printing service whose equipment prints at a set 300dpi (I assume this is
300ppi and "dpi" is being used as a generalisation) and my slide scanner is
capable of 14bit/4000spi... if I am only looking to have, say, a number of
5" x 7.5" prints made from a particular 35mm scan - would scanning get me
the same printed result (in terms of detail, colour depth etc) if I only
scan at 1500spi? Or should I scan at max resolution and assume the software
at the printers will resample the resulting huge file down to the required
size for printing?

Reason I ask is that I often have to adjust white/black points, and other
curves on the scan before saving the file and I have a suspicion that these
adjustments are best done with as much DATA as possible to give smoother
effects - hence I high bit-depth, high resolution scan... however I would
much prefer to upload smaller file sizes and there is this nagging feeling
that whatever kind of resampling is done at the other end it is likely to be
detremental to the image quality that I took the trouble to produce...

For archive purposes I assume the general recommendation is a high
resolution, high bit depth TIFF file for those particularly important
photographs.

Deep Thought wrote:
> This may be perceived as a stupid question but I use an on-line photo
> printing service whose equipment prints at a set 300dpi (I assume this is
> 300ppi and "dpi" is being used as a generalisation) and my slide scanner is
> capable of 14bit/4000spi... if I am only looking to have, say, a number of
> 5" x 7.5" prints made from a particular 35mm scan - would scanning get me
> the same printed result (in terms of detail, colour depth etc) if I only
> scan at 1500spi? Or should I scan at max resolution and assume the software
> at the printers will resample the resulting huge file down to the required
> size for printing?
>
> Reason I ask is that I often have to adjust white/black points, and other
> curves on the scan before saving the file and I have a suspicion that these
> adjustments are best done with as much DATA as possible to give smoother
> effects - hence I high bit-depth, high resolution scan... however I would
> much prefer to upload smaller file sizes and there is this nagging feeling
> that whatever kind of resampling is done at the other end it is likely to be
> detremental to the image quality that I took the trouble to produce...
>
> For archive purposes I assume the general recommendation is a high
> resolution, high bit depth TIFF file for those particularly important
> photographs.

There are a few things to know about scanning -

The higher resolution the scan - the larger the file.
The larger size the image - the larger the file.
TIF files are larger then JPG files and drive the lab technician
printing the photo crazy. (It is best to use JPG files, this is sort
of a standard file type.)

You don't say what size slides you are going to scan, or what scanner
you are using. Also, what software you are using to scan the slides in
with. All of these are going to affect the quality of your scan.

First of all - keep the scanning surface clean. I have a Umax Astra
2200 Scanner. The way it is set up, it get finger prints on the glass
from time to time. I have to take some Windex and clean the glass from
time to time, or a lens cleaning wipe if it is really bad. This really
improves the quality of the scanned image. (This is a stupid thing,
and it is annoying ... but it really changes the quality of the scanned
image in both prints and slides.)

I am yet to get a good quality negative scan. There is a blue mask on
the negatives, and once you remove it from the scanned images, the
quality goes in the toilet.


Now as far as the size to scan - it depends on a number of factors.
You stated the size of the desired output. Also consider that in the
future you many want to make an 8x10 from one of the scans. This is
possible. There are a couple of other factors. The power supply in
your computer, the memory in your computer, the processor in your
computer, the ammount of memory in your computer, what program you are
using to scan photos, what operating system you are using, the amount
of storage space on your computer, (in windows - how much virtual
memory you have allocated), in linux how large of a swap partition you
have. All of these thing have to be considered. I forgot about the
power supply and was crashing my computer trying to do scans of 3x5
photos at 600 dpi.
The computer would reboot for no reason in the middle of a scan. I was
overloading the power supply. The computer only came with a 250 watt
power supply. It now has a larger power supply, and the scanning works
fine.

If you try to scan something too large for you computer - you will lock
the computer up, or it will decide to reboot on its own, or in windows
it will write a data dump file to the hard drive and fill up your hard
drive with garbage files, or all three. None of these are very fun.
In linux, the scans worked fine without too much trouble even with the
lower wattage power supply at the same dpi.

So, you have to experiment and find a good resolution for the printout
you want to make. I would make a test print on an inkjet or laser
printer before sending them to the lab, and see if the result is
acceptable. The inkjet or laser print it not going to be the quality
of a lab print, but it will tell you if your scan is going to be a high
enough quality to get good results from the lab.

On my scanner - for most things I end up scanning at 1200 dpi from a
3x5 or 4x6 print. Slides I try to scan at 2400 or 3600 dpi, as slides
are smaller, sometimes the slides work out at that dpi, and sometimes I
have to scan them in at a lower dpi.

You just have to play and see what works out.

Hope this helps.
Now if anybody can figure out the negatives?

roland