Electronic rescreen technique for halftone pictures

Details Electronic rescreen technique for halftone pictures Electronic rescreen technique for halftone pictures

1979-08-24

1981-03-31

Corbin, John K.

Facsimile and static presentation processing

Facsimile

Recording apparatus

H04N 140

Patent

active

042596947

ABSTRACT:
A method for rescreening a halftone image to produce an edge-enhanced halftone copy from a halftone original. The halftone original is scanned by a raster input scanner and the resultant analog voltage is compared to a reference voltage to produce a one bit per pixel bit stream, where a pixel is defined as the smallest image (picture) element discernable by the system. For example, in a raster input scanner using a CCD array, the smallest picture element, pixel, is the analog voltage output of one CCD cell. This voltage subsequently can be converted to a digital gray scale representation requiring a plurality of bits per pixel, or either analog or digital representation can be compared to an analog or digital reference voltage to produce a one bit pixel. A six bit per pixel gray scale output is produced therefrom by adding an integrated value and an edge enhancement value for each input pixel received. The integrated value is calculated by summing the number of one bits in the seven by nine bit section surrounding each pixel. The edge enhancement value is calculated by determining the difference between the number of one bits in the right and left halves, and upper and lower halves, of the six by seven bit section surrounding each pixel. A set of equations is used to process these differences to produce an edge enhancement value which is added to the integrated value. From this six bit per pixel gray scale output the six bit output can be preserved, or a halftone copy can be produced by any well-known process. A simple and inexpensive circuit to perform the above functions at high data rates is also disclosed.

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Jarvis, J, et al., "A New Technique for Displaying Continuous Tone Images on a Bilevel Display", IEEE Transactions on Communications, vol. COM.-24, No. 8, pp. 891-898, Aug. 1976.
Schroeder, M. R., "Images from Computers", IEEE Spectrum, Mar. 1969, pp. 66-78.

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