Advice for Scanning images
Advice for the good Scanning of images depends largely upon what image you
want to scan, the decision should be based upon the original images' physical size
and what your long term intentions for the image are.
Remember that a good printer outputs at about 360dpi, a monitor displays at
about 72-76 dpi (dots per inch)
The more detail you can capture in the first place will give you more longer term
options, but you cannot put detail in where it wasn't before.
Storage
capacity of your equipment will cap the maximum filesize you are able or prepared to
keep, of course you could keep saving your images to CD's (or DVD's) as you go along.
However CD's and DVD's are only semi-permanent, do not save to CD only
and then expect that in 20 years time you will still be able to access the
images.
Consider that every 5 - 10 years you should physically re-copy your
original CD and then keep the new copy as well.
Saving any image as a .jpeg (.jpg) is usually a detail losing process,
it naturally compresses data (images) to make a smaller filesize.
Therefore
opening a .jpeg and then saving it, even without any changes may lose
data (quality) from the original - even though you may have done
nothing to the original between opening and re-saving it. However,
just opening and closing a jpeg should not affect its image quality.
So bringing these points together:
Always make one high quality scan relevant to the size/quality of the
original, that you then save, name and archive. Work on copies made from this original.
For a negative or a slide or any other highly detailed, but small image, you
need to use the maximum or near maximum natural resolution of the scanner.
However this should not be an interpolated resolution, so for most scanners this would often mean using 1200dpi,
or 2400dpi or 3200dpi.
The higher numbers such as 6400,9200,12,000 etc are usually
interpolated. This is where the scanner software just puts in extra
dots where it thinks they might / could / should go, this mode
very rarely offers any benefit, and can make filesizes huge.
Update: August 2006
Copying slides (transparencies) to a high quality is proving to be extremely difficult!!
This is an area where having top equipment is probably the only solution. I use an Epson Perfection 3490 Photo scanner which has a slide copying feature. Despite a high resolution (3200dpi optical) it appears near impossible to get enough gamma (light) into the captured image.
Therefore you have to boost the image in Photoshop to regain detail - especially in the shadows - this then introduces
unsightly speckling, and because the resolution is simply not high enough you have to apply sharpening as well.
The end results are very disappointing, with just a 400 by 300 pixel image looking disappointing on a monitor!.
If you view the four RAF Waddington 2005 albums many of the 'flying' images are scans
from slides, many of these when projected are stunning photos, with sharp detail and vibrant colour.
I will have a go with a dedicated slide scanner soon and update with the findings later.
Below is an example scanned image, the original 35mm slide is sharp and colourful and this is 75% of the full frame.
I have created a 640x480 image at 2400dpi. However after extensive retouching/boosting of the image it still looks like a 1960's 'B' movie.
The above is a 99k image, which has virtually all the detail fom the 4MB scan. Extensive testing of alternative
scanning settings was trialled including up to 100MB filesizes...
If you look at the inset photo, the image just doesn't have detail or sharpness, especially in the shadow areas.
Scanning from a print, photo or other image, is more of a compromise
based on how high you perceive the quality of the original
and how much storage space you are prepared to allow for your scanned
pictures.
A good rule of thumb would be to scan at around 300 - 600dpi,
as this will match the highest quality you are likely to acheive
by printing the image (unless you are looking 20 - 30 years ahead).
However if you only ever intend to display on a monitor
then you could scan at 72 - 100dpi in order to make filesizes smaller,
remember that if you lose the original you will never be able
to put detail back in to your scanned images. 76dpi may suffice
for images for emails and the web, but not if from a small original
image.
So save a Big original, archive this scanned picture and then
use copies of this original, that you can then manipulate in your
usual photo / scanner editing software for your intended purpose.
Never re-save back over the original image.
It isn't really possible to give just one straight forward recommendation
because there isn't just one answer, but many differing compromises
based upon personal needs.
I hope this information helps.
