Saturday, November 19, 2005

Full resolution and digital content management systems

My attempt at briefly and concisely explaining full resolution images and digital content management systems (specifically ContentDM and MDID):

Best practices recommend that digitized images be stored as large tiff files. Tiff files are lossless compressed files that are considered archival masters. Generally, tiff files are not intended to be stored on a web server.

Most digitization standards and best practices consider full resolution images to be between 1000 and 3000 pixels on the long side, with 3000 pixels most common. Exceptions are for printed materials and original images that can not support the high level of detail. The term full resolution does not imply file type. On most current monitors, images of 1000 pixels in width fill the screen. Therefore, larger images (1000-3000 pixels) can be “zoomed in” to show greater detail. The needs of the project will determine what resolution (pixel size) of image is appropriate.

Digital content management systems (like ContentDM and MDID) were originally intended as a means of discovery for the original full resolution tiff file being stored off line. MDID users can download the largest image stored on the server, and ContentDM users can zoom in to the level of detail supported by the size of the image stored on the server. The images stored on these servers should be jpegs. Tiffs require too much storage space and, due to the large file size, have slow download times. MDID will not allow uploads larger than 16 MB, which most tiff images surpass.

In the digitization workflow, after images are scanned as full resolution tiffs, the next step is to create derivative jpeg images to upload to the server. The resolution (pixel size) of these derivative files depends on the needs of the project. ContentDM users can incorporate this step into the image upload by using image optimization in full resolution archiving. MDID users need to do this before uploading the files.

Full resolution archiving in ContentDM provides a means of organization for large tiff images that are used to create the derivative images stored on the server. ContentDM populates one of the metadata fields with information on where the full resolution tiff file is stored. MDID metadata creators need to provide this information by hand. Without full resolution archiving in ContentDM, the original tiff file is uploaded, and the location of the original file in not noted in the metadata. Because ContentDM will only show 600-1000 pixels of any image, it is important to be able to find the full resolution image being stored off line.

Draft digitization standards from the Indiana Digital Library Summit


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