3. Conversion

INTRODUCTION
Digital image capture must take into consideration the technical processes involved in converting from analog to digital representation as well as the attributes of the source documents themselves: physical size and presentation, level of detail, tonal range, and presence of color. Documents may also be characterized by the production process used to create them, including manual, machine, photographic, and more recently, electronic means. Further, all paper- and film-based documents will fall into one of the following five categories that will affect their digital recording.

Document Types

• Printed Text/Simple Line Art—distinct edge-based representation, with no tonal variation, such as a book containing text and simple line graphics
• Manuscripts—soft, edge-based representations that are produced by hand or machine, but do not exhibit the distinct edges typical of machine processes, such as a letter or line drawing
• Halftones—reproduction of graphic or photographic materials represented by a grid of variably sized, regularly spaced pattern of dots or lines, often placed at an angle. Includes some graphic art as well, e.g., engravings
• Continuous Tone—items such as photographs, watercolors, and some finely inscribed line art that exhibit smoothly or subtly varying tones
• Mixed—documents containing two or more of the categories listed above, such as illustrated books

Document Types: Left to right - printed text, manuscript, halftone, continuous tone, and mixed.

© 2000-2003 Cornell University Library/Research Department