3. Conversion

Key Concepts

scanning factors
rich digital master


  continuous-tone   halftone
proposed method guidelines
additional reading



Contents Selection- intro Intro- digital images Conversion-rich digital master Quality Control Metadata Technical Presentation Digital Preservation Management Continuing Education
Conversion-scanning factors Conversion-benchmarking text Conversion-benchmarking

There are compelling preservation, access, and economic reasons for creating a rich digital master image file (sometimes referred to as an archival image) in which all significant information contained in the source document is represented.

Creating a rich digital master can contribute to preservation in at least three ways:

  1. Protecting vulnerable originals. The image surrogate must be rich enough to reduce or eliminate the user's need to view the original.
  2. Replacing originals. Under certain circumstances, digital images can be created to replace originals or used to produce paper copies or Computer Output Microfilm. The digital replacement must satisfy all research, legal, and fiscal requirements.
  3. Preserving digital files. It is easier to preserve digital files when they are captured consistently and well documented. The expense of doing so is more justifiable if the files offer continuing value and functionality.

A digital master should be capable of supporting a range of users' needs through the creation of derivatives for printing, display, and image processing. The richer the digital master, the better the derivatives in terms of quality and processibility. User expectations will likely be more demanding over time--the digital master should be rich enough to accommodate future applications. Rich masters will support the development of cultural heritage resources that are comparable and interoperable across disciplines, users, and institutions.

Creating a high quality digital image may cost more initially, but will be less expensive than creating a lower quality image that fails to meet long-term requirements and results in the need to re-scan. Labor costs associated with identifying, preparing, inspecting, indexing, and managing digital information far exceed the costs of the scan itself.

The key to image quality is not to capture at the highest resolution or bit depth possible, but to match the conversion process to the informational content of the original, and to scan at that level--no more, no less. In doing so, one creates a master file that can be used over time. Long-term value should be defined by the intellectual content and utility of the image file, not limited by technical decisions made at the point of conversion.

No More, No Less: As resolution increases, image quality will level off.

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Conversion - scanning factorsConversion - benchmarking text

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