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Electronic image dpi


#1

Greetings to my Orchid friends. A while back there was a thread that
addressed resolution for electronic images. One comment was that 300
dpi was standard for publishing purposes [thanks Susan] and the other
comment was that 300dpi would be fine for images printed aprox 5x7.

My question - I will be archiving my slide history into electronic
format. What resolution would allow me to produce a quality image at
8x10? Scanning at the higher resolution is more expensive and of
course the files will be larger. I realize I can always go down in
resolution for specific applications [a copy reduced to 72 for web].

Of course I can always have a few done and test the results but I am
hoping that someone has already crossed this bridge. I have been
talking to the photo people and basically the message is “we can do
whatever you want”. The point is I don’t have enough experience to
know what I want.

Thanks in advance
Orchid Rules!
Karla in So.
California


#2

What is wanted is a source that will produce an image with a
resolution of 300 dots per inch in an 8 x 10 inch image. This would
be 2400 dots by 3000 dots.

A standard 35mm slide measures one inch by one and one-half inches.
This will enlarge to an image 8 inches by 12 inches, and the extra
two inches will be cut off to leave an 8 x 10 inch image. To be sure
to have enough resolution for 300 dots per inch for the 10-inch
length, you must have it for the 12-inch length. Hence, you will
need 300 times 12, or 3600 dots in the 1-1/2 inch slide, which is
2400 dots per inch. So have your 35mm slides scanned at 2400 dots
per inch.

Be aware that this scan resolution is for the full image being used
in the 8 x 10 inch size. If you are going to crop out unwanted image
area before enlarging to an 8 x 10, you will need to scan at a
higher resolution to retain the 300 dots per inch resolution. If you
have eliminated all waste space before taking the picture, which is
always a good idea, then you can always go with the 2400 dots per
inch resolution to end up with a 300 dpi 8 x 10 image. This is, by
the way, an 8.64 megapixel file size. You should be able to fit
about 65 such pictures on a CD.

There are many electronic picture formats. The two used for internet
pictures, “JPG” and “GIF”, are not particularly suited for printing
a 300 dots per inch. Use the format recommended by your photo people
as that format can be fairly easily converted to JPG or GIF.
(Neither JPG nor GIF hold as much picture as other
formats; you can’t go from them to a “good” print format because you
won’t have all the image you need.)

Regards,