Re digitized images of all kinds
At the Huntington Archive where we do almost excliusively images ranter
that text documents, we have found the file size a particularly difficult
problesm which we are still discussing. Archival storage of images, has
for us been at the maximum "usable" resolution, and not the maximum
possible resolution. With scanners that go up to 14,000dpi and true 5,600
dpi, hundred Gb files are possible but who wants all that data from a
single sheet of paper or film?
In practice, we have found that 360dpi at 100% scaling an A4 size sheet is
more than enough. Smaller objects are sometimes enlarged to 150% or 200%,
again depending on the amount of detail and potential usage. This
resolution goes far beyond the needs of most OCR programs that I know of.
If texture or grain of a paper or other type of support of a document is
important to the item, then one may have to go to a higher resolution
archival image. With only a very few exceptions we have not found this
necessary.
Web images are always transferred across the web at 72dpi no matter what
the original scanning resolution was. if you save them in TIFF, they can
be tiled in Mr. Sid or with JTIP. This allows a user to see an overview
section as an about 1024 by 768 screen size but at 72dpi. By selecting
subsections the viewing applets then selects the appropriate "detail" tile
to bring up. so files for strictly web use should be sized to the exact
screen size that is necessary and at 72dpi. this is always a much smaller
file than the original scan which we archive at the maximum size in TIFF.
>I would add that particularly when dealing with greyscale or colour images,
>files of that size become particularly difficult to handle from a storage
>and manipulation standpoint. A 600 dpi colour image can be as large as 100
>mb (for a letter/A4 page) in uncompressed format -- most image editing
>applications require 3 to 4 times the size of any image for system memory to
>work with the image; hence 300 mb to 400 mb of RAM just for the application
>(never mind the system itself).
>
>Based on our experiences, images approximately 1000 pixels high in typical
>situations provides an image that is quite readable on the web. However,
>this will depend on your source material. A better rule of thumb (as opposed
>to overall resolution) is to look at the resultant height of the characters
>on screen.
>
>Hope this helps.
>
>Tim
>
>--------
>Tim Au Yeung
>Manager of Digitization Initiatives
>Information Resources (Press)
>University of Calgary
>voice: 403.220.8975
>email: ytau (at) ucalgary.ca
>
>
>----- Original Message -----
>From: Susan Stekel <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Friday, January 07, 2000 9:34 AM
>Subject: Re: Greetings, and question on Scanned Images
>
>
>>
>>
>> > My question therefore is this:
>> >is there a recommended level of quality for scanning this kind of image
>for
>> >web-site use? Would, for example, 600 dpi be of sufficient quality, or do
>> >people generally aim for a higher specification?
>> >
>> >Apologies if my question displays my appalling ignorance...
>> >cheers
>> >john
>>
>>
>> You're not ignorant at all, and certainly not in any appalling way.
>> Scanning at 600 dpi has become the standard approach for most projects
>such
>> as yours. It'll give you good data capture of the original. When
>handling
>> any historical material, it's best to scan it once, and properly, to avoid
>> having to re-scan (and damage) the documents. So, scan at a high
>resolution
>> (like 600 dpi) and scan to a non-proprietary file format, such as TIFF.
>>
>> The real issue is: what image are you going to put online? A 600 dpi
>image
>> is a huge file that will take ages to download. Also, you don't really
>get
>> the benefit of all that data, since most computer monitors have a fairly
>> poor resolution (not above the 75-100 dpi range). Once you have the 600
>dpi
>> master files, you can make low-resolution derivatives from those files, in
>a
>> web-ready format such as JPEG, that will load much faster while still
>> presenting a readable image.
>>
>> My comments are only the briefest of summaries on this topic -- but I
>don't
>> want to weigh down the list. If you'd like clarification on anything I've
>> said or would like to talk further, please feel free to contact me at the
>> e-mail listed below.
>>
>> Best wishes,
>> Susan
>> ***********************************************
>> Susan Stekel, M.A., M.S.I.
>> Library and Archives Specialist
>> --------------------------------------------------------------
>> Northern Micrographics Inc.
>> 2004 Kramer St. P.O. Box 2287
>> La Crosse, WI 54602-2287
>> (608) 781-0850 ext. 137 (voice)
>> (608) 781-3883 (fax)
>> [log in to unmask]
>>
>>
>>
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