What is the best way to go about digitising maps and construction/architectural designs for including as part of an online digital library?
I’ve been asked by a project what is the best way to digitize
architectural drawings and maps that are larger than what most
scanners can handle in preparation of loading them into online
collection. What options should I consider?
[Asked by Walter on 2 September 2009]
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Comments
Digitising items bigger than about A3 in size is likely to require some specialist equipment, but there are a couple of different ways to go about it that we know of. The first is by paying for a specialised high resolution digital scan, and the second is through an overhead rig using a digital or medium format camera.
New Zealand Micrographic Services in partnership with the National Library run the Heritage Materials Imaging Facility. They use a Cruse scanner, which is a high resolution scanner used for heritage art, manuscripts and maps. The cost of each scan is quite expensive, so it is not a solution for high volumes. Here’s some background on that http://www.micrographics.co.nz/nzmicrographics/nzmshmif/tabid/279/default.aspx.
If going down the route of using an overhead camera, there can also be some outlay if you are doing it in-house. The kind of overhead rigs used by the likes of the National Library of New Zealand, for instance, tend to be of a professional archival standard and somewhat expensive. It is possible to build your own rig fairly cheaply, but that will only get you part of the way. Depending on the size of the maps, there is so much dense information on them that it can be very hard to photograph them digitally without a specialised camera, lens and lighting. The test of this is whether your camera can resolve the smallest detail such as a place name or dotted boundary line and not create optical distortion at the corners of the map. Also test for even lighting across the whole document.
Most large maps are still photographed with a medium format film camera and then the negative or transparency is digitised – this may be the cheapest route. There are a number of companies that do map photography, and there have been a number of digitisation projects in New Zealand. You can see some of them on the RODI database http://ndf.natlib.govt.nz/cgi-bin/rodi/search?s=maps . Note these projects are mainly aimed at web access, not digital preservation – solutions like the HMIF or keeping film negatives need to be considered if preservation is a goal.
The other thing to strongly consider for maps is the delivery mechanism – you may need a specialised web viewer (such as Zoomify http://www.zoomify.com/ ) if users are to be able to zoom in and out of a large image. It is possible to host images as PDFs, but larger maps may be in the 10-20 Megabyte size and are hard for users to navigate. Auckland City Council however has been able to put up smaller maps as JPEGs such as this one http://tinyurl.com/l8u4p3 without too much trouble it seems.
We have been digitizing maps for a number of years, and I presented a paper on our process in 2004, although the way we do it now is still basically the same.
http://tinyurl.com/lvgynv
Our photographers use a large format camera which gives a 5 × 4 in. neg. which is then scanned.
Ian Snowdon
Maps Librarian
Auckland City Libraries – Tamaki Pataka Korero
As previously mentioned one option is overhead copying by digital and or photographic means. 300dpi is the accepted guideline in resolution to ensure the detail can be reproduced.
Depending on the material, another option is contact scanning through a ‘plan scanner’. In this process the maps and plans are fed through and scanned quickly and more cost effectively this way, but with more risk of damage. Not recommended for heritage materials, but if the collection are duplicates it may be appropriate. These map scanners may have reduced colour depth E.g. they may be 4-bit colour rather than 8 or 16, and will not have the same level of colour accuracy for reproduction.
Hi, just to add a few thoughts from NZMS. As David notes above it does depend on the nature and condition of the maps. A wide format scanner will be a cheaper option if you are prepared to put them through a roller scanner (with or without a mylar sleeve) and quality isn’t essential.
The flat bed options as Lewis notes are down to a digital camera mounted above the items or the Cruse Scanner at HMIF with its 1.5 × 1 metre scan bed. Then it becomes a question of quality and how much information you need to capture (usually governed by what is the smallest meaningful element in the map or plan), and then what you want to do with the file and the original e.g. do you want a surrogate so that you can retire the original , would you want to reproduce it at a size greater than 1:1? If it is going on the web what level of magnification does it need to sustain.
File size for large items certainly needs to be considered. The Cruse can capture 10,000 by 15,000 pixels and at 24 bit RGB this will create a 430 MB file, which even at A0 size will give you enough detail to count the paper fibres (assuming you can get the file open?) It is by far the biggest “digital camera” in the country.
Scanning A0, A1 & A2, sized maps at 300 ppi will produce uncompressed Tiff files in the order of:
A0 – 390 MB
A1 – 200 MB
A2 – 100 MB
Saved as JPEG with Photoshop’s maximum quality this drops the files sizes to ~15, 7 and 4-5 MB respectively.
For the Web about 2 MB is more reasonable so you will need to consider resizing your access images to A3 and/or applying more compression, or other canny viewing tools…
NB. There is an image of an A1+ original topographical map on our website resized to A3 at 300ppi http://www.micrographics.co.nz/nzmicrographics/nzmshmif/samples/tabid/287/default.aspx which is about 2.5 MB.
Resolution is one aspect of quality, the lighting and the array in the scanner/camera also makes a big difference. As well as being laser aligned for precision our Cruse has a 10,000 pixel trilinear array. There is no barrel distortion or chromatic aberration, which can be issues with digital cameras, and the trilinear array is capturing greater colour fidelity than the bayer array in a camera which is interpolating (guessing) a lot more of the data.
Quality in turn affects price. So then we have the “distasteful” question of how much it costs and what one can afford.
As a point of reference rather than a sales pitch an A2 scan on the Cruse (at 300 ppi) currently costs from $ 26.
Hope this helps! And remember it’s not just the technology, it’s understanding the principles of image capture and what you want to achieve.
On a presentation note We have our maps scanned at a good resolution – and provide a 768 longest length jpg as a presentation image.
We have found that using Zoomify allows us to provide a great level of detail – with out giving away our paid for high resolution file – and making it quite usable. See http://christchurchcitylibraries.com/Heritage/Maps/174746-3.asp
and click on the View enlargable version (with Zoomify) link below the image