Browse Prior Art Database

Variable Area Quadra Receptor Scan Head

IP.com Disclosure Number: IPCOM000081763D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Thompson, DR: AUTHOR

Abstract

This quadra-receptor scan head and shutter arrangement permits measurement of reflective density of four equally proportioned but variable total area segments, for digital halftone generation with enlargement/ reduction scaling.

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Variable Area Quadra Receptor Scan Head

This quadra-receptor scan head and shutter arrangement permits measurement of reflective density of four equally proportioned but variable total area segments, for digital halftone generation with enlargement/ reduction scaling.

Digital halftones have been generated by measuring the reflective density of incremental areas of a continuous tone photographic print, and then constructing clusters of dots whose total area in relation to the total area available is a measure of the original incremental grayness. This has been previously accomplished by scanning at a high resolution and obtaining many small measurements of grayness for each larger sample area. The measurements are then summed and averaged over the appropriate area for that particular scale, to arrive at a single resultant gray level.

Fig. 1 illustrates an arrangement which provides a simple, direct measurement of only four reflective densities in quadrature no matter what the size of the sample area, and averaging only the four for the resultant single gray level. As the shutter blade moves down or up, the effective sampled area decreases or increases uniformly and always in the diamond shape, as shown in Fig. 2.

A compensating amplifier for each of the four sensor outputs would adjust to provide uniform output with fixed source illumination, as the area changes with shuttering. Alternatively, an optical attenuator could be provided, e.g., density wedge, polarizer...