I am working on digitising standards for the Imperial War Museum in London.
While 300dpi is very commonly used it is derived from a prepress standard for printing pictures in a book. In terms of capturing the detail you need at least 2 pixels to pick up a detail (the most commonly quoted figure), however you can still miss the detail if it does not line up with the pixels, so go for 2.5 - 3 pixels to capture detail. The equipment is another important consideration, from your remark it sounds like you are using a flat bed scanner which for delicate material could in fact destroy or damage the item. You can also use a high end camera such a Hasselbad. The other consideration is colour management which is often misunderstood (and to complex for a short email) you need to have linear set up and use colour patches with each capture so you can gauge the reproduction. Always keep the original un-changed make any adjustments on a copy which then becomes the working master. A camera (Hasselblad H3DII-50) has a fixed number of pixels and presuming most of the material is A4 / US Letter in size you can work out the capture original 8.5 in by 11in - camera pixels, 6321 by 8176 divide the pixels by the size gives 720 pixels (need to take into account the portions of the original and the camera ) On a flat bed scanner you can scan at 1200 pixel per inch which captures all the detail in a full colour printed image but does produce a very large file so you need a computer capable of handling it. I would suggest a camera as it is quicker to capture an image and the lighting can be a more even copy set up. A scanner can produce more pixels for the inch but in general the lighting and the speed can work against one, but it is cheaper than a camera set up. Mark Evely Digital Systems Manager Collection Management 020 7091 3081 07976 297034
