SPEC Kit 329: Managing Born-Digital Special Collections and Archival Materials · 143
RUcore. Born Digital Still Images
IBB • RUcore Preservation Standards • Born Digital Still Images Rev: 11/18/2010
Page 4 of 7
digital images that are of comparable overall quality. In such a case, ppi only comes into play when a
user wishes to print the digital image, in which case this value can be changed at will to suit the user’s
needs. As a result, the value of importance in digital photography is not how many pixels per inch make
up an image, but the overall pixel count, or number of total pixels, that are used to represent the image.
With current technology, this value is frequently expressed in Megapixels (MP).
Unaltered Originals: RUcore places the utmost importance on the ability to have an archival
digital master, that is unaltered or unedited in any way. This requirement ensures that we can refer to
this original at any time, should any edits or calibrations we perform on our derivate presentation
versions of an object become unsuitable for display as technology changes. Producing such images are
relatively easy when digitizing analog formats. The matter becomes trickier, however, when dealing
with digital camera equipment.
Born Digital File Formats: JPG, RAW Image file formats and the unique challenges they present
To be sure, no single digital camera architecture will suit every photography application and so, camera
vendors design and construct a vast assortment of digital cameras that vary in size, resolution and
capability. A major challenge for dealing with digital photography is the diversity of equipment that is
out in the field, and the resulting file formats that they generate.
Entry-Level Consumer Digital Cameras pose the greatest issue because they typically output files
using the JPEG file format, with very lossy compression. To their credit, such cameras permit beginners
and casual users to capture important and even historic moments with a minimum of effort and skill, and
a great deal of archived content would not exist without casual photographers using such equipment,
where more advanced and skilled photographers are simply not present. However, their ease also
presents a disadvantage: entry-level cameras heavily process the images the capture, and the resulting
image files are suboptimal for archival purposes without, at the very least, a file format change to an
uncompressed TIFF format.
“Pro-sumer” and Professional Cameras typically provide the option to process and compress captured
images into JPEG files similar to the consumer counterparts, but also tend to provide an option to yield
camera raw image files. A camera raw image file contains minimally processed data as retrieved
directly from the image sensor of the digital camera. Raw files are so named because they are not yet
processed and therefore are not ready to be printed or edited with a bitmap graphics editor. Normally,
the image is processed by conversion, where precise adjustments can be made before creating a
"positive" file format such as an uncompressed TIFF or JPG file. Similar to a film negative, a raw
digital image may have a wider dynamic range or contain more color information than can be provided
using currently used file formats for presentation and access (TIFF, JPG, etc.), and preserves most of the
information of the captured image. The purpose for a raw file is to achieve minimal loss of image data
obtained from the sensor, and the conditions surrounding the capturing of the image (the technical
metadata). In the field of photography, there is a pervasive, erroneous belief that RAW represents a
single file format. In fact there are hundreds of raw image formats in use by different models of digital
equipment, and the formats can vary from one vendor to the next, and even among different camera
models made by the same manufacturer.
To get around the issue of non-standard and widely-disparate raw image formats, a standardized
open file format, developed by Adobe Systems, Inc. and called “Digital Negative” (DNG) was
developed in 2004, and is updated regularly with backward comaptibility. DNG is based upon the TIFF
image standard, but encapsulates the additional sensor data in most proprietary raw image formats. In
addition to Adobe software, the DNG file format is accessible and can be read by over 40 additional