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Technical Information

Digitising the Pont manuscripts

Nearly all the images that appear on the Pont maps website were scanned in early 2000, using a PhaseOne Powerphase camera back, with an internal charged coupled device (CCD) resolution of 7,000 x 7,000 pixels. This created 24-bit full-colour TIFF images of up to 143 megabytes. This camera back, with a front end Hasselblad camera and Zeiss lens, was mounted on a vertical sliding stand pointing down at the maps, illuminated by cool flourescent (low ultra-violet) lighting. Due to the vulnerability and value of the Pont manuscripts, as treasures of the Library, the scanning equipment was carefully set up to minimise any possibility of damage or alteration to the original maps.

The decisions behind using this higher-resolution camera rested upon earlier scanning of the Pont maps in 1996-97 using a Kontron ProgRes 3012 camera. This had an internal CCD resolution of only 3072 x 2032 pixels, creating 20 megabyte images, and so images of larger Pont maps, above A3 size, fell below 200 pixels per inch (ppi). This was inadequate for seeing most small map details and names. To compensate for this, a mosaic of images of small parts of the map were captured at higher resolutions of 550 ppi, with the camera positioned closer to the map, but navigating between separate images of the same sheet, and seaming images together both proved difficult. The images also exhibited problems of red and green colour banding, which unfortunately became quite prominent upon enhancement.

The PhaseOne camera allowed the whole of each Pont map sheet to be captured at resolutions of between 300-500 ppi, suitable for most research purposes, and it did not create the colour banding problems of the Kontroncamera. For this reason, the PhaseOneimages are predominantly used on this website, with occasional Kontron thumbnail details, where highest resolutions are required.

Compression and web delivery

We were keen to exploit the advantages of wavelet compression technology, which in recent years has allowed large images to be reduced to about 1/30th of their original file size without any visible degradation in image quality. The multi-resolution compression formats of MrSID (Multi-Resolution Seamless Image Database) and ECW (Enhanced Compressed Wavelet) lend themselves well to serving map images, which need to be zoomed to detailed levels and panned (moved sideways). We chose the MrSID format, and currently use the MrSID Content Serverto display images within Internet browsers, without a plug-in. Users may also download an optional free browser plug-in with enhanced viewing options of the MrSID image itself, such as image rotation (very important for the Pont maps).