Whoa, he's back!
It's almost been a solid two months since I graced these electronic pages with my portentous ramblings on archival concepts and practice. As part of a year-long (yeah, let's see if I can sustain this) blog series on digital archives I am going to jump into some "beginning" concepts. It's a big topic so I wanted to start in some familiar territory; let's talk the relationship of formats in a repository environment. Shall we - - - -
We are going to start simple with the concept of the Master copy and the derivative copy, or access copy. This relationship is commonly constructed when digitizing archival materials for a number of reasons:
1) Master copies tend to be large files
2) Due to that file size they are hard to provide access to in a web environment
3) Master copies are not always system-independant
4) Master copies can be considered the "authentic" version, copy or original
Whereas, access copies tend to have these qualities:
1) Much more system-independant sometimes
2) Usually compressed in some manner to save space, but not loss information
3) Easier to provide access to in a web environment
So, brass tacks means that when scanning a photograph from a family album or other legacy source, we will typically create one master copy and one access copy. They are both maintained to archival standards and both get a full suite of metadata, but the master copy rarely is accessed or opened and usually lives in a "dark archives." <-- A repository for master copies, rarely, if ever, accessed by patrons.
We format these files according to standards used by the National Archives and Records Administration (NARA) which specifies these standards for the production of digital master files and digital access copies:
Bit-depth: 8 bits per channel
File Format: TIFF
*Typically no adjustments are done to the photograph with the exception of rotation to ensure a level representation. Images may be cropped to within a few pixels of the item border. We sometimes refer to this as an "evidentiary border" because it provides evidence of the completeness of an item.
DPI: 300 (down to 200 in some cases)
Color: RGB (derived from Master copy)
Bit-depth: 8 bits per channel (derived from Master copy)
File Format: JPEG
*Adjustments are inherited from the Master copy.
After the items are created, one is stored in a dark archives and the other is uploaded to a public facing access-portal (this could be an online exhibit, EDRMS, CMS, or other access-system). The patrons and users are able to access the files as needed and get what they are looking for, and we can be assured that we always have an "original" master to make a derivative from in case the original gets corrupted, deleted, or we need to verify an access copy against the master (I haven't seen this happen more than once, but that doesn't mean it might not become more common as people become more aware of what can be seen--and hidden--in a digital file/space).
I hope you enjoyed this brief dip into digital archival waters. I'll be back in the next week or so with more information and hopefully pictures!
All the best,