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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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 x 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