After understanding all kinds of the digital images, how do you think that librarians could benefit from them? I am asked to use the Tiff type of images in the document delivery in Mills Music library. Obviously, librarians want to provide the best digital copies in the document delivery service. Can you think about the other services in the libraries that could use other types of images with smaller size? How do librarians choose between lossy and lossless types?
As Sarah pointed out in her lecture, it is usually about trading quality for file size. Big files take up space and load slowly. Keely Merchant gave a good description of how this works in her digital library/archive in her interview. An original jpeg is submitted and saved, a large tiff is made and saved by the administrators for preservation purposes and a (probably smaller) jpeg is put up on the website for viewing.
Another reason to use a low-quality image is for a thumbnail. When I have worked on my own websites in the past, I have used tiny, low-quality gifs for thumbnails that then link to larger jpegs when you click on them. The California Digital Libraries’ guidelines suggest gifs for thumbnails. Very lossy small jpegs are also used.
Still another reason for keeping quality down might be to prevent people from using your library’s images in ways you don’t want them to. The Minnesota Historical Society Library has a wonderful online collection including many beautiful historic photographs (http://greatriversnetwork.org/index.php?brand=cms). Search results display listings along with very small (less than 10KB) jpeg thumbnails. If you click a thumbnail you get to see a larger (about 50KB) jpeg that is big enough to enjoy the image but still very small in terms of reproducing a print copy for publication, or even enlarging to fill the span of a webpage. MNHS file sizes and types conform closely to the California Digital Libraries’ guidelines with the exception that these access image jpegs are actually considerably smaller (500 pixels measured on the long side instead of 800 pixels recommended by CDL)
Of course MNHS does not want you to publish these photos without paying for the rights. Perhaps their extra small access images are an effort to thwart unauthorized use? I purchased the right to publish some photos from the MNHS collection for a CD booklet project and they sent me wonderfully huge tiff versions that I could zoom into a lot (some seemed to be endlessly deep when I got the big files, revealing details impossible to see in the jpeg).
(For example, look at this image (http://collections.mnhs.org/cms/largerimage.php?irn=10279199&catirn=10667064) and see if you can tell there is a second saloon further down the boardwalk called “Minnie Ha Ha Saloon,” or that there are two people relaxing in one of the boats and at least three people walking on the boardwalk! All that is easy to see in the amazing tiff file.)