[PADG:1760] Re: Picture Library: sizes and resolution

["Jacob Nadal" <jnadal@xxxxxxxxxxx>]

It's worthwhile to benchmark a few representative images to determine
what the minimum acceptable level of detail is. From there you can
extrapolate to a good set of guidelines for different image types. To do
this, measure the size in mm of the smallest detail you wish to capture
in the original image (perhaps a line on a map, the dot on a lower case
"i", etc...). You'll need to choose how much fidelity you wish to have
in the digital image - if minimal fidelity is acceptable, only one or
two pixels might be assigned to the detail, while 3-5 pixels will give
much greater detail. Divide the number of pixels you wish to use by the
size of the detail, and multiply by 25 (the number of mm in an inch) to
find the dpi at which to scan.

For instance, if I want to be able to distinguish a line that is 0.07 mm
wide in the original, and need a high degree of fidelity, I would scan
at (3 pixels / .07 mm) * 25 ~= 1072 dpi. In this case, I'd actually
choose to scan a little higher, at 1200 dpi, since this is a pretty
common resolution for scanning hardware and gives me that much more
flexibility.

You'll also need to make a choice of color depth - 1-bit (black and
white) is fine for most text and line art, 8 bit grayscale is often
needed for halftones and black & white photography, and 24 bit color for
color photography and illustration.

Cornell has a good tutorial on imaging that discusses this in more
depth: http://www.library.cornell.edu/preservation/tutorial/index.html

It's also helpful to contact your printer and see what their
requirements are, as far as resolution and file format for printable
images. For print, I think that tiff remains the standard format and
resolutions around of 300 - 600 dpi are commonly requested.

Best of luck,
Jacob Nadal

Acting Head of Preservation, Indiana University Libraries
jnadal@xxxxxxxxxxx

-----Original Message-----
From: owner-padg@xxxxxxx [mailto:owner-padg@xxxxxxx] On Behalf Of Philip
Merrill
Sent: Tuesday, July 16, 2002 1:38 AM
To: padg@xxxxxxx
Subject: [PADG:1759] Re: Picture Library: sizes and resolution


This may not be ideal, but the practice I'm used to is JPEG's no more
han 2,000 pixels wide and thumbnails about 200 pixels wide. The big
images tend to be about 300K which is not too bad. Personally I prefer
TIFFs but they're always at least 1MB that size and range up to about
3.5 MB. Also, you will need much better resolution if you're planning to
use a big color image like for a "centerfold." The digital sizes for
these are so intense that I wouldn't use this for every image. Just
calculate that at a minimum you need a pixel for each of the dots in
inches-times-dpi. If you want leeway to color-correct and photo-edit the
image, you'll need two or three times that. Again I like TIFF. Once when
we wanted 1 picture for our Web site, our magazine graphic artist sent
over a TIFF on ZIP disk that was 80MB! Good luck finding the right happy
medium for your organization. PHIL :) Philip Merrill


----- Original Message -----
From: Sebastian John
To: padg@xxxxxxx
Sent: Monday, July 15, 2002 8:50 AM
Subject: [PADG:1757] Picture Library: sizes and resolution


The publishing group where I work is building a digital library. The
pictures will be for the newspaper and the magazine that the group
publishes. Would someone suggest the ideal image size and the resolution
the pictures need to be scanned so as to benefit both the users.

Regards

Sebastian John
Picture Coordinator
The Week
Malayala Manorama
Cochin 682036
Kerala, India
Tel:  0091-484-316285
Fax: 0091-484-315745